Software-RAID HOWTO
Linas Vepstas, linas@linas.org
v0.54, 21 November 1998
ÃÖ Èñö ironyjk@kldp.org
2000³â 3¿ù 1ÀÏ
RAID ´Â ''Redundant Array of Inexpensive Disks'' ÀÇ ¾àÀÚ·Î, °¢°¢ÀÇ
µð½ºÅ© µéÀ» ¹¾î¼ ºü¸£°í ¾ÈÀüÇÑ µð½ºÅ© ½Ã½ºÅÛÀ» ¸¸µå´Â °ÍÀÌ´Ù. RAID
´Â ÇϳªÀÇ µð½ºÅ©¿¡ ºñÇØ ¿À·ù¸¦ ´ëºñÇÒ ¼ö ÀÖÀ¸¸ç, ¼Óµµ¸¦ Áõ°¡ ½ÃŲ´Ù.
RAID stands for ''Redundant Array of Inexpensive Disks'', and is meant
to be a way of creating a fast and reliable disk-drive subsystem out
of individual disks. RAID can guard against disk failure, and can
also improve performance over that of a single disk drive.
ÀÌ ¹®¼´Â Linux MD kernel È®Àå¿¡ °üÇÑ tutorial/HOWTO/FAQ ¹®¼ÀÌ´Ù. MD
È®ÀåÀº RAID-0,1,4,5 ¸¦ ¼ÒÇÁÆ®¿þ¾î ÀûÀ¸·Î Áö¿øÇÏ°í, ÀÌ°ÍÀ» ÅëÇØ ¿ì¸®´Â
Ưº°ÇÑ Çϵå¿þ¾î³ª µð½ºÅ© ÄÜÆ®·Ñ·¯ ¾øÀÌ RAID ¸¦ »ç¿ëÇØ º¼¼ö ÀÖ´Ù.
This document is a tutorial/HOWTO/FAQ for users of the Linux MD kernel
extension, the associated tools, and their use. The MD extension
implements RAID-0 (striping), RAID-1 (mirroring), RAID-4 and RAID-5 in
software. That is, with MD, no special hardware or disk controllers
are required to get many of the benefits of RAID.
______________________________________________________________________
¸ñÂ÷
1. ¼Ò°³
2. RAID ÀÇ ÀÌÇØ
3. ¼³Ä¡¿Í ¼³Á¤
4. ¿¡·¯ÀÇ º¹±¸
5. ¼³Ä¡¹®Á¦ÀÇ ÇØ°á
6. Hardware & Software ÀÇ Áö¿ø
7. ÀÌ¹Ì ¼³Ä¡µÈ ½Ã½ºÅÛ ¼öÁ¤Çϱâ.
8. ¼º´É°ú µµ±¸, ÀϹÝÀûÀÎ °Íµé¿¡ °üÇÑ ¸ÛûÇÑ Áú¹®µé.
9. °í °¡¿ë¼º(High-Availability) RAID
10. ´äº¯À» ±â´Ù¸®´Â Áú¹®µé.
11. Ãß°¡µÇ¾îÁö±â ¹Ù¶ó´Â ±â´Éµé..
______________________________________________________________________
¸Ó¸®¸»
This document is copyrighted and GPL'ed by Linas Vepstas
(linas@linas.org). Permission to use, copy, distribute this
document for any purpose is hereby granted, provided that the
author's / editor's name and this notice appear in all copies
and/or supporting documents; and that an unmodified version of
this document is made freely available. This document is
distributed in the hope that it will be useful, but WITHOUT ANY
WARRANTY, either expressed or implied. While every effort has
been taken to ensure the accuracy of the information documented
herein, the author / editor / maintainer assumes NO
RESPONSIBILITY for any errors, or for any damages, direct or
consequential, as a result of the use of the information
documented herein.
º» ¹®¼ÀÇ È²´çÇÏ°í ¹«Ã¥ÀÓÇÑ ¹ø¿ªÀ¸·Î ÀÎÇÑ Á¤½ÅÀû ¹°¸®Àû ÇÇÇظ¦
¿ªÀڴ åÀÓÀ» ÁöÁö ¾Ê½À´Ï´Ù. ^^ (¹ø¿ªÀÌ Ã³À½ÀÌ´Ù º¸´Ï, ÀÌ ¹®¼¿¡
¿À¿ªÀÌ Á¶±Ý(?) ÀÖ½À´Ï´Ù.) ÀÌ ¹®¼´Â GPLÀ» µû¸¨´Ï´Ù. ¿À¿ª°ú
À߸øµÈ, °»½ÅÇØ¾ß ÇÒ Á¤º¸¿¡ °üÇؼ´Â Àú¿¡°Ô ¸ÞÀÏÀ» Áֽñâ
¹Ù¶ø´Ï´Ù. ¹ø¿ªÀ̶ó°í Çϱä Çߴµ¥ ¾û¼ºÇϱ⠱×Áö ¾ø±º¿ä. Á» ´õ
ÀÚ¼¼ÇÑ ¹ø¿ªÀ» ÇÏ°í ½Í±ä ÇÏÁö¸¸. Àß ¸ð¸£´Â °Íµµ ¸¹°í ´õ ÇÏ°í
½ÍÀº °Íµµ ¸¹¾Æ¼ ^^;
RAID´Â µð½ºÅ©ÀÇ Ãß°¡·Î ½Ã½ºÅÛÀÇ ½Å·Ú¼ºÀ» Çâ»ó½Ãų¼ö ÀÖÀ¸³ª,
À߸øµÈ »ç¿ëÀ¸·Î ÀÎÇØ ¿ªÈ¿°ú¸¦ ³¾ ¼öµµ ÀÖ´Ù. ƯÈ÷ , RAID´Â
µð½ºÅ© ÀÚüÀÇ ¿À·ù¿¡ ´ëºñÇÑ °ÍÀÌÁö. »ç¿ëÀÚÀÇ ½Ç¼ö³ª, Àü¿øÀÇ
ºÒ·®¿¡ ´ëºñÇϵµ·Ï ¼³°èµÈ °ÍÀÌ ¾Æ´Ï´Ù. Àü¿øÀÇ ºÒ·®°ú, °³¹ß Ä¿³Î,
±×¸®°í, °ü¸®ÀÚÀÇ ½Ç¼ö´Â µ¥ÀÌÅ͸¦ ¼Õ»ó½Ãų °ÍÀÌ°í, RAID ´Â
¹é¾÷¹æ¹ýÀÌ ¾Æ´Ô¿¡ À¯ÀÇÇ϶ó.
RAID, although designed to improve system reliability by adding
redundancy, can also lead to a false sense of security and
confidence when used improperly. This false confidence can lead
to even greater disasters. In particular, note that RAID is
designed to protect against *disk* failures, and not against
*power* failures or *operator* mistakes. Power failures, buggy
development kernels, or operator/admin errors can lead to
damaged data that it is not recoverable! RAID is *not* a
substitute for proper backup of your system. Know what you are
doing, test, be knowledgeable and aware!
1. ¼Ò°³
1. Q: RAID ¶õ ¹«¾ùÀΰ¡?
A
RAID ´Â ''Redundant Array of Inexpensive Disks' ÀÇ ¾àÀÚ·Î,
°¢°¢ÀÇ µð½ºÅ© µéÀ» ¹¾î¼ ºü¸£°í ¾ÈÀüÇÑ µð½ºÅ© ½Ã½ºÅÛÀ»
¸¸µå´Â °ÍÀÌ´Ù.
RAID stands for "Redundant Array of Inexpensive Disks", and
is meant to be a way of creating a fast and reliable disk-
drive subsystem out of individual disks. In the PC world,
"I" has come to stand for "Independent", where marketing
forces continue to differentiate IDE and SCSI. In it's
original meaning, "I" meant "Inexpensive as compared to
refrigerator-sized mainframe 3380 DASD", monster drives
which made nice houses look cheap, and diamond rings look
like trinkets.
2. Q: ÀÌ ¹®¼´Â ¹«¾ùÀΰ¡?
A:
ÀÌ ¹®¼´Â Linux MD kernel È®Àå¿¡ °üÇÑ tutorial/HOWTO/FAQ
¹®¼ÀÌ´Ù. MD È®ÀåÀº RAID-0,1,4,5 ¸¦ ¼ÒÇÁÆ®¿þ¾î ÀûÀ¸·Î
Áö¿øÇÏ°í, ÀÌ°ÍÀ» ÅëÇØ ¿ì¸®´Â Ưº°ÇÑ Çϵå¿þ¾î³ª µð½ºÅ©
ÄÜÆ®·Ñ·¯ ¾øÀÌ RAID ¸¦ »ç¿ëÇØ º¼¼ö ÀÖ´Ù.
This document is a tutorial/HOWTO/FAQ for users of the Linux
MD kernel extension, the associated tools, and their use.
The MD extension implements RAID-0 (striping), RAID-1
(mirroring), RAID-4 and RAID-5 in software. That is, with
MD, no special hardware or disk controllers are required to
get many of the benefits of RAID.
This document is NOT an introduction to RAID; you must find
this elsewhere.
3. Q: Linux Ä¿³ÎÀº ¾î¶² ·¹º§ÀÇ RAID ¸¦ Áö¿øÇϴ°¡?
A: RAID-0 Àº 2.x ¹öÀüÀÇ ¸®´ª½º Ä¿³ÎµéÀÌ Áö¿øÇÑ´Ù. ÀÌ°ÍÀº
ÀÌÇØÇϱ⠽±°í, ¸î¸îÀÇ ¸Å¿ì Å« À¯Áî³Ý ´º½º ¼¹ö¿¡ »ç¿ëµÈ´Ù.
Striping (RAID-0) and linear concatenation are a part of the
stock 2.x series of kernels. This code is of production
quality; it is well understood and well maintained. It is
being used in some very large USENET news servers.
RAID-1, RAID-4, RAID-5 ´Â Ä¿³Î 2.1.63 ÀÌ»óÀÇ ¹öÀü¿¡¼
Áö¿øÇÑ´Ù. 2.0.x ¿Í 2.1.xÀÇ Ä¿³ÎµéÀº ÆÐÄ¡¸¦ ÇØ¾ß ÇÑ´Ù.
Ä¿³ÎÀ» ¾÷±×·¹À̵å ÇØ¾ß ÇÑ´Ù°í »ý°¢ÇÏÁö ¸¶¶ó. ¾÷±×·¹À̵庸´Ù.
ÆÐÄ¡°¡ ÈξÀ ½¬¿ï °ÍÀÌ´Ù.
RAID-1, RAID-4 & RAID-5 are a part of the 2.1.63 and greater
kernels. For earlier 2.0.x and 2.1.x kernels, patches exist
that will provide this function. Don't feel obligated to
upgrade to 2.1.63; upgrading the kernel is hard; it is
*much* easier to patch an earlier kernel. Most of the RAID
user community is running 2.0.x kernels, and that's where
most of the historic RAID development has focused. The
current snapshots should be considered near-production
quality; that is, there are no known bugs but there are some
rough edges and untested system setups. There are a large
number of people using Software RAID in a production
environment.
RAID-1 hot reconstruction has been recently introduced
(August 1997) and should be considered alpha quality.
RAID-5 hot reconstruction will be alpha quality any day now.
A word of caution about the 2.1.x development kernels: these
are less than stable in a variety of ways. Some of the
newer disk controllers (e.g. the Promise Ultra's) are
supported only in the 2.1.x kernels. However, the 2.1.x
kernels have seen frequent changes in the block device
driver, in the DMA and interrupt code, in the PCI, IDE and
SCSI code, and in the disk controller drivers. The
combination of these factors, coupled to cheapo hard drives
and/or low-quality ribbon cables can lead to considerable
heartbreak. The ckraid tool, as well as fsck and mount put
considerable stress on the RAID subsystem. This can lead to
hard lockups during boot, where even the magic alt-SysReq
key sequence won't save the day. Use caution with the 2.1.x
kernels, and expect trouble. Or stick to the 2.0.34 kernel.
4. Q: ¾îµð¿¡¼ Ä¿³ÎÀÇ ÆÐÄ¡¸¦ ±¸ÇÒ ¼ö ÀÖ³ª¿ä?
A: Software RAID-0 and linear mode are a stock part of all
current Linux kernels. Patches for Software RAID-1,4,5 are
available from
<http://luthien.nuclecu.unam.mx/~miguel/raid>. See also the
quasi-mirror <ftp://linux.kernel.org/pub/linux/dae
mons/raid/> for patches, tools and other goodies.
5. Q: Linux RAID ¿¡ °üÇÑ ´Ù¸¥ ¹®¼µéÀÌ ÀÖ³ª¿ä?
A:
o Generic RAID overview:
<http://www.dpt.com/uraiddoc.html>.
o General Linux RAID options:
<http://linas.org/linux/raid.html>.
o Latest version of this document:
<http://linas.org/linux/Software-RAID/Software-
RAID.html>.
o Linux-RAID mailing list archive:
<http://www.linuxhq.com/lnxlists/>.
o Linux Software RAID Home Page:
<http://luthien.nuclecu.unam.mx/~miguel/raid>.
o Linux Software RAID tools:
<ftp://linux.kernel.org/pub/linux/daemons/raid/>.
o How to setting up linear/stripped Software RAID:
<http://www.ssc.com/lg/issue17/raid.html>.
o Bootable RAID mini-HOWTO:
<ftp://ftp.bizsystems.com/pub/raid/bootable-raid>.
o Root RAID HOWTO: <ftp://ftp.bizsystems.com/pub/raid/Root-
RAID-HOWTO>.
o Linux RAID-Geschichten:
<http://www.infodrom.north.de/~joey/Linux/raid/>.
6. Q: ÀÌ ¹®¼¿¡ ´ëÇØ ´©±¸¿¡°Ô ºÒÆòÇØ¾ß ÇÏÁÒ?
A: Linas Vepstas slapped this thing together. However, most
of the information, and some of the words were supplied by
o Bradley Ward Allen <ulmo@Q.Net>
o Luca Berra <bluca@comedia.it>
o Brian Candler <B.Candler@pobox.com>
o Bohumil Chalupa <bochal@apollo.karlov.mff.cuni.cz>
o Rob Hagopian <hagopiar@vu.union.edu>
o Anton Hristozov <anton@intransco.com>
o Miguel de Icaza <miguel@luthien.nuclecu.unam.mx>
o Marco Meloni <tonno@stud.unipg.it>
o Ingo Molnar <mingo@pc7537.hil.siemens.at>
o Alvin Oga <alvin@planet.fef.com>
o Gadi Oxman <gadio@netvision.net.il>
o Vaughan Pratt <pratt@cs.Stanford.EDU>
o Steven A. Reisman <sar@pressenter.com>
o Michael Robinton <michael@bzs.org>
o Martin Schulze <joey@finlandia.infodrom.north.de>
o Geoff Thompson <geofft@cs.waikato.ac.nz>
o Edward Welbon <welbon@bga.com>
o Rod Wilkens <rwilkens@border.net>
o Johan Wiltink <j.m.wiltink@pi.net>
o Leonard N. Zubkoff <lnz@dandelion.com>
o Marc ZYNGIER <zyngier@ufr-info-p7.ibp.fr>
Copyrights
o Copyright (C) 1994-96 Marc ZYNGIER
o Copyright (C) 1997 Gadi Oxman, Ingo Molnar, Miguel de
Icaza
o Copyright (C) 1997, 1998 Linas Vepstas
o By copyright law, additional copyrights are implicitly
held by the contributors listed above.
Thanks all for being there!
2. RAID ÀÇ ÀÌÇØ
1. Q: RAID´Â ¹«¾ùÀΰ¡? ¿Ö ³ª´Â ¾ÆÁ÷ »ç¿ëÇØ º¸Áö ¾Ê¾Ò´Â°¡?
A: RAID ´Â ¿©·¯°³ÀÇ µð½ºÅ©¸¦ ¿ª¾î¼, ¼Óµµ¿Í, ¾ÈÀü¼ºÀÌ ÁÁÀº
ÇϳªÀÇ ÇüÅ·Π¸¸µå´Â °ÍÀÌ´Ù. RAID ´Â ¿©·¯°¡Áö ÇüÅ°¡ ÀÖ°í,
±× ÇüŸ¶´Ù °¢°¢ÀÇ Àå´ÜÁ¡À» °¡Áö°í ÀÖ´Ù. ¿¹¸¦ µé¸é RAID
·¹º§ 1 Àº µÎ°³(ȤÀº ÀÌ»ó)ÀÇ µð½ºÅ©¿¡ °°Àº µ¥ÀÌÅÍÀÇ º¹»çº»À»
³Ö´Â °ÍÀÌ´Ù. µ¥ÀÌÅÍ°¡ º¹»çµÈ °¢ µð½ºÅ©¿¡¼ µ¥ÀÌÅ͸¦ °¡Á®¿À±â
¶§¹®¿¡ Àд ¼Óµµ´Â »¡¶óÁú °ÍÀÌ´Ù. Ãß°¡ÀûÀ¸·Î º¹»çµÈ
µ¥ÀÌÅÍ´Â ÇϳªÀÇ µð½ºÅ©°¡ ±úÁ³À» ¶§ ¾ÈÁ¤¼ºÀ» Á¦°øÇÒ °ÍÀÌ´Ù.
RAID ·¹º§¿¡ ÀÇÇÑ ´Ù¸¥ ¹æ¹ýÀº, ¿©·¯°³ÀÇ µð½ºÅ©¸¦ ÇϳªÀÇ
µð½ºÅ©·Î ¹´Â °ÍÀÌ´Ù. ±×°ÍÀº °£´ÜÇÑ º¹»ç¿¡ ºñÇØ Á» ´õ ¸¹Àº
ÀúÀå·üÀ» Á¦°øÇÒ °ÍÀÌ´Ù, ¶ÇÇÑ, Àб⠾²±â¸¦ À§ÇÑ ¼º´É Çâ»óÀ»
½ÃÅ°¸é¼, ¿©ÀüÈ÷ ¿À·ù¿¡ ´ëºñÇÑ Àû´çÇÑ ¿©À¯°ø°£À» ³²°ÜµÑ
°ÍÀÌ´Ù.
RAID is a way of combining multiple disk drives into a
single entity to improve performance and/or reliability.
There are a variety of different types and implementations
of RAID, each with its own advantages and disadvantages.
For example, by putting a copy of the same data on two disks
(called disk mirroring, or RAID level 1), read performance
can be improved by reading alternately from each disk in the
mirror. On average, each disk is less busy, as it is
handling only 1/2 the reads (for two disks), or 1/3 (for
three disks), etc. In addition, a mirror can improve
reliability: if one disk fails, the other disk(s) have a
copy of the data. Different ways of combining the disks
into one, referred to as RAID levels, can provide greater
storage efficiency than simple mirroring, or can alter
latency (access-time) performance, or throughput (transfer
rate) performance, for reading or writing, while still
retaining redundancy that is useful for guarding against
failures.
RAID´Â µð½ºÅ© ¿À·ù¿¡ ´ëºñÇÒ ¼ö ÀÖÁö¸¸, Àΰ£ÀÇ ½Ç¼ö³ª,
ÇÁ·Î±×·¥ÀÇ ¿À·ù¿¡´Â ´ëºñÇÒ ¼ö ¾ø´Ù. (RAID ÇÁ·Î±×·¥ ÀÚüµµ
¿À·ù¸¦ Æ÷ÇÔÇÒ ¼ö ÀÖ´Ù.) net »ó¿¡´Â RAID ¼³Ä¡¿¡ Àͼ÷Ä¡ ¾ÊÀº
°ü¸®ÀÚµéÀÌ ±×µéÀÇ µ¥ÀÌÅ͸¦ ¸ðµÎ ÀÒ¾î¹ö¸®´Â ±×·± ºñ±ØÀûÀÎ
À̾߱⠵éÀÌ ¸¹´Ù. RAID´Â ¹é¾÷ÀÇ ´ëü ÇÒ ¼ö ¾øÀ½¿¡ ÁÖÀÇÇ϶ó!
Although RAID can protect against disk failure, it does not
protect against operator and administrator (human) error, or
against loss due to programming bugs (possibly due to bugs
in the RAID software itself). The net abounds with tragic
tales of system administrators who have bungled a RAID
installation, and have lost all of their data. RAID is not
a substitute for frequent, regularly scheduled backup.
RAID ´Â Çϵå¿þ¾î ÀûÀ¸·Î, Ưº°ÇÑ µð½ºÅ© ÄÜÆ®·Ñ·¯·Î, ¶Ç´Â,
Ä¿³Î ¸ðµâ °°Àº ¼ÒÇÁÆ®¿þ¾î ÀûÀ¸·Î ±¸ÇöµÉ ¼ö ÀÖ´Ù. RAID
Çϵå¿þ¾î "µð½ºÅ© ÄÜÆ®·Ñ·¯"´Â µð½ºÅ© µå¶óÀ̺꿡 ÄÉÀ̺íÀ»
¿¬°áÇÒ¼ö ÀÖ°Ô ÇØÁÖ´Â °ÍÀÌ´Ù. ÀϹÝÀûÀ¸·Î lISA/EISA/PCI/S-
Bus/MicroChannel ½½·Ô¿¡ ÀåÂøÇÒ¼ö ÀÖ´Â Ä«µåÇü½ÄÀ̳ª, ¾î¶²
°ÍµéÀº ÀϹÝÀûÀÎ ÄÁÆ®·Ñ·¯¿Í µð½ºÅ©»çÀ̸¦ ¿¬°áÇØ´Â ¹Ú½º
Çü½ÄÀÌ´Ù.
RAID can be implemented in hardware, in the form of special
disk controllers, or in software, as a kernel module that is
layered in between the low-level disk driver, and the file
system which sits above it. RAID hardware is always a "disk
controller", that is, a device to which one can cable up the
disk drives. Usually it comes in the form of an adapter card
that will plug into a ISA/EISA/PCI/S-Bus/MicroChannel slot.
However, some RAID controllers are in the form of a box that
connects into the cable in between the usual system disk
controller, and the disk drives. Small ones may fit into a
drive bay; large ones may be built into a storage cabinet
with its own drive bays and power supply.
ÃÖ½ÅÀÇ ºü¸¥ CPU¸¦ »ç¿ëÇÏ´Â RAID Çϵå¿þ¾î´Â ÃÖ°íÀÇ ¼Óµµ¸¦
³»±ä ÇÏÁö¸¸, ±×¸¸Å ºñ½Ò °ÍÀÌ´Ù. ÀÌÀ¯´Â ´ëºÎºÐÀÌ º¸µå»ó¿¡
ÃæºÐÇÑ DSP ¿Í ¸Þ¸ð¸®¸¦ °¡Áö°í Àֱ⠶§¹®ÀÌ´Ù. ¿À·¡µÈ RAID
Çϵå¿þ¾î´Â DSP¿Í ij½¬ÀÇ º´¸ñÇö»óÀ¸·Î ÃÖ½ÅÀÇ CPU¸¦ »ç¿ëÇÏ´Â
½Ã½ºÅÛÀÇ ¼Óµµ¸¦ ÀúÇϽÃų¼ö ÀÖ´Ù. ¶§·Î´Â, ÀϹÝÀûÀÎ Çϵå¿þ¾î¿Í
¼ÒÇÁÆ®¿þ¾î RAID ¸¦ »ç¿ëÇÏ´Â °Íº¸´Ù ´õ ´À¸± °ÍÀÌ´Ù. Çϵå¿þ¾î
RAID°¡ ¼ÒÇÁÆ®¿þ¾î RAID¿¡ ºñÇØ ÀåÁ¡ÀÌ ÀÖÀ» ¼ö ÀÖÁö¸¸, ÃÖ±Ù
´ëºÎºÐÀÇ µð½ºÅ© µå¶óÀ̺êµé¿¡°Õ ±×·¸Áö ¾Ê´Ù.? RAID
Çϵå¿þ¾î´Â ÀϹÝÀûÀ¸·Î ´Ù¸¥ ¸ÞÀÌÄ¿¿Í ¸ðµ¨ÀÇ Çϵåµé¿¡°Ô
ȣȯ¼ºÀ» Á¦°øÇÏÁö ¾ÊÁö¸¸, ¸®´ª½º»óÀÇ ¼ÒÇÁÆ®¿þ¾î RAID´Â ¾î¶²
Ưº°ÇÑ ¼³Á¤¾øÀÌ ´ëºÎºÐÀÇ Çϵå¿þ¾îµéÀÌ Àß µ¹¾Æ°¥ °ÍÀÌ´Ù.
The latest RAID hardware used with the latest & fastest CPU
will usually provide the best overall performance, although
at a significant price. This is because most RAID
controllers come with on-board DSP's and memory cache that
can off-load a considerable amount of processing from the
main CPU, as well as allow high transfer rates into the
large controller cache. Old RAID hardware can act as a "de-
accelerator" when used with newer CPU's: yesterday's fancy
DSP and cache can act as a bottleneck, and it's performance
is often beaten by pure-software RAID and new but otherwise
plain, run-of-the-mill disk controllers. RAID hardware can
offer an advantage over pure-software RAID, if it can makes
use of disk-spindle synchronization and its knowledge of the
disk-platter position with regard to the disk head, and the
desired disk-block. However, most modern (low-cost) disk
drives do not offer this information and level of control
anyway, and thus, most RAID hardware does not take advantage
of it. RAID hardware is usually not compatible across
different brands, makes and models: if a RAID controller
fails, it must be replaced by another controller of the same
type. As of this writing (June 1998), a broad variety of
hardware controllers will operate under Linux; however, none
of them currently come with configuration and management
utilities that run under Linux.
¼ÒÇÁÆ®¿þ¾î RAID´Â Ä¿³Î ¸ðµâ·Î ¼³Á¤Çϸç, °ü¸® µµ±¸µîµµ ¸ðµÎ
¼ø¼öÇÑ ¼ÒÇÁÆ®¿þ¾î ÀûÀ¸·Î ÀÌ·ç¾îÁ® ÀÖ´Ù. ¸®´ª½º RAID
½Ã½ºÅÛÀº IDE, SCSI and Paraport drives °°Àº Àú¼öÁØ
µå¶óÀ̹ö¿Í block-device interface À§¿¡ ¾ãÀº ÃþÀ¸·Î Á¸ÀçÇÑ´Ù.
ext2fs ³ª, DOS-FATµîÀÇ ÆÄÀϽýºÅÛÀº block-device
interfaceÀ§¿¡ ¾òÇô ÀÖ´Ù. ¼ÒÇÁÆ®¿þ¾î RAID´Â ¼ÒÇÁÆ®¿þ¾îÀûÀ¸·Î
¸Å¿î ÀÚ¿¬½º·¯¿î °ÍÀ̸ç, Çϵå¿þ¾îÀû ±¸Çöº¸´Ù À¯¿¬ÇÑ °ÍÀÌ´Ù.
´ÜÁ¡À¸·Î´Â Çϵå¿þ¾î ½Ã½ºÅÛº¸´Ù CPU cycle°ú Àü¿øÀ» Á¶±Ý ´õ
¼Ò¸ðÇÑ´Ù´Â °ÍÀÌÁö¸¸, °¡°ÝÀÌ ºñ½ÎÁö´Â °ÍÀº ¾Æ´Ï´Ù.
¼ÒÇÁÆ®¿þ¾î RAID´Â ÆÄƼ¼Ç ´ÜÀ§·Î ¿òÁ÷À̸ç, °¢°¢ÀÇ ÆÄƼ¼ÇÀ»
¹¾î¼ RAID ÆÄƼ¼ÇÀ» ¸¸µé ¼öµµ ÀÖ´Ù. ÀÌ°ÍÀº Çϵå¿þ¾îÀû
±¸Çö°ú Å©°Ô ´Ù¸¥ Á¡À̸ç, µð½ºÅ©µé Àüü¸¦ Çϳª·Î ¹¾î¹ö¸±
¼öµµ ÀÖ´Ù. ±×°ÍÀº Çϵå¿þ¾îÀûÀ¸·Î´Â ¿î¿µÃ¼Á¦·ÎÀÇ ¼³Á¤À»
°£´ÜÇÏ°í ¸í¹éÈ÷ ÇÒ¼ö ÀÖ°í, ¼ÒÇÁÆ®¿þ¾îÀûÀ¸·Î´Â Á» ´õ ´Ù¾çÇÑ
¼³Á¤À¸·Î º¹ÀâÇÑ ¹®Á¦µé¿¡ Á¢±ÙÇÒ ¼ö ÀÖ´Ù.
Software-RAID is a set of kernel modules, together with
management utilities that implement RAID purely in software,
and require no extraordinary hardware. The Linux RAID
subsystem is implemented as a layer in the kernel that sits
above the low-level disk drivers (for IDE, SCSI and Paraport
drives), and the block-device interface. The filesystem, be
it ext2fs, DOS-FAT, or other, sits above the block-device
interface. Software-RAID, by its very software nature,
tends to be more flexible than a hardware solution. The
downside is that it of course requires more CPU cycles and
power to run well than a comparable hardware system. Of
course, the cost can't be beat. Software RAID has one
further important distinguishing feature: it operates on a
partition-by-partition basis, where a number of individual
disk partitions are ganged together to create a RAID
partition. This is in contrast to most hardware RAID
solutions, which gang together entire disk drives into an
array. With hardware, the fact that there is a RAID array
is transparent to the operating system, which tends to
simplify management. With software, there are far more
configuration options and choices, tending to complicate
matters.
ÀÌ ±ÛÀÌ ¾²¿©Áö´Â ½ÃÁ¡( 1998³â 6¿ù)¿¡¼, LinuxÇÏÀÇ RAIDÀÇ
¼³Á¤Àº ¾î·Á¿î °ÍÀÌ°í, ¼÷·ÃµÈ ½Ã½ºÅÛ °ü¸®ÀÚ°¡ ¼³Á¤ÇÏ´Â °ÍÀÌ
ÁÁÀ» °ÍÀÌ´Ù. ¹æ¹ýÀº ³Ê¹« º¹ÀâÇÏ°í , startup scriptµéÀÇ
¼öÁ¤À» ÇÊ¿ä·Î ÇÑ´Ù. µð½ºÅ© ¿¡·¯·ÎºÎÅÍÀÇ º¹±¸´Â Æò¹üÇÑ °ÍÀÌ
¾Æ´Ï°í »ç¶÷ÀÇ ½Ç¼ö·Î À̾îÁö±â ½±´Ù. RAID´Â Ãʺ¸ÀÚ¸¦ À§ÇÑ
°ÍÀÌ ¾Æ´Ï´Ù. ¼Óµµ Çâ»ó°ú ¾ÈÀü¼ºÀ» ¾ò±â Àü¿¡ ÀÇ¿ÜÀÇ
º¹ÀâÇÔ¿¡ Ç㸦 Âñ¸®±â ½¬¿ì´Ï Á¶½ÉÇϱ⠹ٶõ´Ù.. ƯÈ÷, ¿äÁò
µð½ºÅ©µéÀº ¹ÏÀ» ¼ö ¾øÀ» ¸¸Å ¾ÈÀüÇÏ°í ¿äÁò CPU¿Í ÄÁÆ®·Ñ·¯´Â
ÃæºÐÈ÷ °·ÂÇÏ´Ù. ´ç½ÅÀº ÁúÁÁ°í ºü¸¥ Çϵå¿þ¾îÀÇ ±¸ÀÔÀ¸·Î Á»´õ
½±°Ô ¿øÇÏ´Â ¸¸ÅÀÇ ¼Óµµ¿Í ¾ÈÁ¤¼ºÀ» ¾òÀ» ¼ö ÀÖÀ» °ÍÀÌ´Ù.
As of this writing (June 1998), the administration of RAID
under Linux is far from trivial, and is best attempted by
experienced system administrators. The theory of operation
is complex. The system tools require modification to
startup scripts. And recovery from disk failure is non-
trivial, and prone to human error. RAID is not for the
novice, and any benefits it may bring to reliability and
performance can be easily outweighed by the extra
complexity. Indeed, modern disk drives are incredibly
reliable and modern CPU's and controllers are quite
powerful. You might more easily obtain the desired
reliability and performance levels by purchasing higher-
quality and/or faster hardware.
2. Q: RAID ·¹º§ÀÌ ¹«¾ùÀΰ¡¿ä? ¿Ö ±×·¸°Ô ¸¹Àº°¡¿ä? ¾î¶»°Ô ±¸ºÐÇÏÁÒ?
A: °¢ ·¹º§¸¶´Ù, ¼Óµµ¿Í »ç¿ë°ø°£, ¾ÈÁ¤¼º, °¡°ÝÀÇ Æ¯¼ºÀÌ
´Ù¸£´Ù. ¸ðµç RAID ·¹º§ÀÇ °úÀ×»ç¿ë°ø°£ÀÌ µð½ºÅ© ¿À·ù¸¦
´ëºñÇØ ÁÖ´Â °ÍÀº ¾Æ´Ï´Ù. RAID-1°ú RAID-5°¡ °¡Àå ¸¹ÀÌ
»ç¿ëµÇ¸ç, RAID-1´Â Á»´õ ³ªÀº ¼Óµµ¸¦ ³» ÁÙ °ÍÀ̸ç, RAID-5´Â
Á» ´õ µð½ºÅ©ÀÇ ¿©À¯°ø°£À» ¸¹ÀÌ ³²°ÜÁÙ°ÍÀÌ´Ù. ÇÏÁö¸¸, ¼Óµµ°¡
·¹º§¿¡ ÀÇÇؼ ¿ÏÀüÈ÷ °áÁ¤µÇ´Â °ÍÀº ¾Æ´Ï´Ù. ¼Óµµ´Â »ç¿ëÇÒ
ÇÁ·Î±×·¥, stripe,block,file µéÀÇ Å©±âµî ´Ù¾çÇÑ ¿äÀο¡ ¸¹Àº
¿µÇâÀ» ¹Þ´Â´Ù. ÀÌ¿¡ °üÇؼ´Â ÀÌ µÚ¿¡¼ ÀÚ¼¼È÷ ´Ù·ê °ÍÀÌ´Ù.
The different RAID levels have different performance,
redundancy, storage capacity, reliability and cost
characteristics. Most, but not all levels of RAID offer
redundancy against disk failure. Of those that offer
redundancy, RAID-1 and RAID-5 are the most popular. RAID-1
offers better performance, while RAID-5 provides for more
efficient use of the available storage space. However,
tuning for performance is an entirely different matter, as
performance depends strongly on a large variety of factors,
from the type of application, to the sizes of stripes,
blocks, and files. The more difficult aspects of
performance tuning are deferred to a later section of this
HOWTO.
¾Æ·¡¿¡¼´Â Linux ¼ÒÇÁÆ®¿þ¾î RAID ±¸ÇöÀÇ ´Ù¸¥ ·¹º§µé¿¡ ´ëÇؼ
¼³¸íÇÏ°í ÀÖ´Ù.
The following describes the different RAID levels in the
context of the Linux software RAID implementation.
o ¼±Çü RAID (RAID-linear) Àº ¿©·¯°³ÀÇ ÆÄƼ¼ÇµéÀ» ¿¬°áÇØ
ÇϳªÀÇ Å« °¡»ó ÆÄƼ¼ÇÀ» ¸¸µå´Â °ÍÀÌ´Ù. ÀÌ°ÍÀº ÀÛÀº
µå¶óÀ̺êµéÀ» ¿©·¯°³ °¡Áö°í ÀÖ°í ÀÌ°ÍÀ» ÇϳªÀÇ Å«
ÆÄƼ¼ÇÀ¸·Î ¸¸µé°íÀÚ ÇÒ¶§ À¯¿ëÇÒ °ÍÀÌ´Ù. ÇÏÁö¸¸, ÀÌ
¿¬°áÀº ¾ÈÀü¼ºÀ» Á¦°øÇÏÁö ¾Ê´Â´Ù. ÇϳªÀÇ µð½ºÅ©¿¡ ¿À·ù°¡
³ª¸é, ¹¿©ÀÖ´Â ÆÄƼ¼Ç Àüü°¡ ¿À·ù°¡ ³¯°ÍÀÌ´Ù.
is a simple concatenation of partitions to create a
larger virtual partition. It is handy if you have a
number small drives, and wish to create a single, large
partition. This concatenation offers no redundancy, and
in fact decreases the overall reliability: if any one
disk fails, the combined partition will fail.
o RAID-1 ´Â "mirroring" ½ÃÅ°´Â °ÍÀÌ´Ù. µÎ°³ ÀÌ»óÀÇ °°Àº
Å©±â¸¦ °¡Áø ÆÄƼ¼ÇµéÀÌ ¸ðµÎ ºí·°´ë ºí·°À¸·Î °°Àº µ¥ÀÌÅ͸¦
°¡Áö°Ô µÈ´Ù. ¹Ì·¯¸µÀº µð½ºÅ© ¿À·ù¿¡ ¾ÆÁÖ °·ÂÇÏ´Ù.
µð½ºÅ© Çϳª°¡ ¿À·ù³µÀ» ¶§¿¡µµ, ÆÄ¼ÕµÈ µð½ºÅ©¿Í ¿ÏÀüÈ÷
¶È°°Àº º¹Á¦º»ÀÌ ÀÖ´Â °ÍÀÌ´Ù. ¹Ì·¯¸µÀº Àб⠿äûÀ» ¸î°³ÀÇ
µð½ºÅ©°¡ ³ª´©¾î ó¸®ÇÔÀ¸·Î½á, I/O°¡ ¸¹Àº ½Ã½ºÅÛÀÇ ºÎÇϸ¦
ÁÙ¿©ÁÙ¼ö ÀÖ´Ù. ÇÏÁö¸¸, »ç¿ë°ø°£ÀÇ ÀÌ¿ëÀ²¿¡¼ º¼ ¶§
¹Ì·¯¸µÀº ÃÖ¾ÇÀÌ´Ù...
is also referred to as "mirroring". Two (or more)
partitions, all of the same size, each store an exact
copy of all data, disk-block by disk-block. Mirroring
gives strong protection against disk failure: if one disk
fails, there is another with the an exact copy of the
same data. Mirroring can also help improve performance in
I/O-laden systems, as read requests can be divided up
between several disks. Unfortunately, mirroring is also
the least efficient in terms of storage: two mirrored
partitions can store no more data than a single
partition.
o Striping Àº ´Ù¸¥ RAID ·¹º§¿¡ ±âº»ÀûÀÎ °³³äÀÌ´Ù. stripe´Â
µð½ºÅ© ºí·°µéÀÌ ¿¬¼ÓÀûÀ¸·Î ºÙ¾îÀÖ´Â °ÍÀÌ´Ù. stripe ´Â
ÇϳªÀÇ µð½ºÅ© ºí·°¸¸Å ªÀ» ¼öµµ ÀÖÀ» °ÍÀÌ°í, ¼ö õ°³ÀÇ
ºí·°µé·Î ÀÌ·ç¾îÁ® ÀÖÀ» ¼öµµ ÀÖÀ» °ÍÀÌ´Ù. RAID µå¶óÀ̹ö´Â
µð½ºÅ© ÆÄƼ¼ÇÀ» stripe ·Î ³ª´ °ÍÀÌ´Ù. RAID ÀÇ ·¹º§Àº
stripe°¡ ¾î¶»°Ô ±¸¼ºµÇ¾ú´Â°¡. ¾î¶² µ¥ÀÌÅ͸¦ ´ã°í
Àִ°¡¿¡ µû¶ó¼ ´Þ¶óÁú °ÍÀÌ´Ù. stripeÀÇ Å©±â¿Í,
ÆÄÀϽýºÅÛ¾ÈÀÇ ÆÄÀÏÀÇ Å©±â, ±×°ÍµéÀÇ µð½ºÅ© ¾È¿¡¼ÀÇ
À§Ä¡°¡ RAID ½Ã½ºÅÛÀÇ ÀüüÀûÀÎ ¼º´ÉÀ» Á¿ìÇÒ °ÍÀÌ´Ù.
(¿ªÀÚ µ¡, stripe´Â ¶ìÀε¥.. Çϳª¿¡ µð½ºÅ©¿¡ Àִ°Ô
¾Æ´Ï¶ó. ¿©·¯°³ÀÇ µð½ºÅ©¿¡¼ °°Àº ºÎºÐÀÌ ¶ì¸¦ ¸¸µå´Â
°ÍÀÌ°ÚÁÒ..)
is the underlying concept behind all of the other RAID
levels. A stripe is a contiguous sequence of disk
blocks. A stripe may be as short as a single disk block,
or may consist of thousands. The RAID drivers split up
their component disk partitions into stripes; the
different RAID levels differ in how they organize the
stripes, and what data they put in them. The interplay
between the size of the stripes, the typical size of
files in the file system, and their location on the disk
is what determines the overall performance of the RAID
subsystem.
o RAID-0 Àº ¼±Çü RAID¿¡ ´õ °¡±õ´Ù. ÆÄƼ¼ÇÀ» stripe µé·Î
³ª´©°í ¹´Â °ÍÀÌ´Ù. ¼±Çü RAIDó·³ °á°ú´Â ÇϳªÀÇ Å«
ÆÄƼ¼ÇÀÌ°í, ±×°ÍÀº °úÀ× °ø°£ÀÌ ¾ø´Ù. ¿ª½Ã ¾ÈÀü¼ºµµ
ÁÙ¾îµç´Ù. ´Ü¼øÇÑ ¼±Çü RAID¿¡ ºñÇØ ¼º´ÉÀÌ Çâ»óµÇ±ä
ÇÏÁö¸¸, ÆÄÀÏ ½Ã½ºÅÛ°ú, stripe ÀÇ Å©±â¿¡ ÀÇÇØ »ý±â´Â
ÆÄÀÏÀÇ ÀϹÝÀûÀÎ Å©±â, ÀÛ¾÷ÀÇ ÇüÅ¿¡ ¸¹Àº ÀÇÁ¸À» ÇÑ´Ù.
is much like RAID-linear, except that the component
partitions are divided into stripes and then interleaved.
Like RAID-linear, the result is a single larger virtual
partition. Also like RAID-linear, it offers no
redundancy, and therefore decreases overall reliability:
a single disk failure will knock out the whole thing.
RAID-0 is often claimed to improve performance over the
simpler RAID-linear. However, this may or may not be
true, depending on the characteristics to the file
system, the typical size of the file as compared to the
size of the stripe, and the type of workload. The ext2fs
file system already scatters files throughout a
partition, in an effort to minimize fragmentation. Thus,
at the simplest level, any given access may go to one of
several disks, and thus, the interleaving of stripes
across multiple disks offers no apparent additional
advantage. However, there are performance differences,
and they are data, workload, and stripe-size dependent.
o RAID-4 ´Â RAID-0 ó·³ stripe·Î ³ª´©´Â ¹æ½ÄÀ» »ç¿ëÇÑ´Ù.
ÇÏÁö¸¸, parity Á¤º¸¸¦ ÀúÀåÇÒ Ãß°¡ÀûÀÎ ÆÄƼ¼ÇÀ» »ç¿ëÇÑ´Ù.
parity ´Â °úÀ× Á¤º¸¸¦ ÀúÀåÇϴµ¥ »ç¿ëµÇ°í, ÇϳªÀÇ
µð½ºÅ©¿¡ ¿À·ù°¡ ³µÀ» ¶§, ³²Àº µð½ºÅ©ÀÇ µ¥ÀÌÅÍ´Â ÆļյÈ
µð½ºÅ©ÀÇ µ¥ÀÌÅ͸¦ º¹±¸Çϴµ¥ »ç¿ëµÉ °ÍÀÌ´Ù. N °³ÀÇ
µð½ºÅ©°¡ ÀÖ°í, ÇϳªÀÇ parity µð½ºÅ©°¡ ÀÖ´Ù¸é, parity
stripe´Â °¢ µð½ºÅ©ÀÇ stripe µéÀÇ XOR ¿¬»êÀ¸·Î °è»êµÉ
°ÍÀÌ´Ù. (N+1) µð½ºÅ©¸¦ °¡Áø RAID-4 ¹è¿ÀÇ ÀúÀå¿ë·®Àº N
ÀÌ µÉ°ÍÀÌ´Ù. ÇÏÁö¸¸, RAID-4´Â ¹Ì·¯¸µ¸¸Å Àд ¼Óµµ°¡
ºü¸£Áö ¾Ê°í ¸Å¹ø µð½ºÅ©¸¦ ¾µ ¶§¸¶´Ù ¿¬»êÀ» ÇÏ°í parity
µð½ºÅ©¿¡ ½á¾ß ÇÑ´Ù. ¶§¹®¿¡ ¾²±â°¡ ¸¹Àº ½Ã½ºÅÛ¿¡´Â ¸Å¹ø
parity µð½ºÅ©¸¦ access ÇØ¾ß Çϱ⠶§¹®¿¡, º´¸ñÇö»óÀÌ
ÀϾ ¼ö ÀÖ´Ù.
interleaves stripes like RAID-0, but it requires an
additional partition to store parity information. The
parity is used to offer redundancy: if any one of the
disks fail, the data on the remaining disks can be used
to reconstruct the data that was on the failed disk.
Given N data disks, and one parity disk, the parity
stripe is computed by taking one stripe from each of the
data disks, and XOR'ing them together. Thus, the storage
capacity of a an (N+1)-disk RAID-4 array is N, which is a
lot better than mirroring (N+1) drives, and is almost as
good as a RAID-0 setup for large N. Note that for N=1,
where there is one data drive, and one parity drive,
RAID-4 is a lot like mirroring, in that each of the two
disks is a copy of each other. However, RAID-4 does NOT
offer the read-performance of mirroring, and offers
considerably degraded write performance. In brief, this
is because updating the parity requires a read of the old
parity, before the new parity can be calculated and
written out. In an environment with lots of writes, the
parity disk can become a bottleneck, as each write must
access the parity disk.
o RAID-5 ´Â °¢ µå¶óÀ̺긶´Ù parity stripe ¸¦ ÀúÀå½ÃÅ´À¸·Î½á
RAID-4ÀÇ ¾²±â º´¸ñÇö»óÀ» ÇÇÇÒ¼ö ÀÖ´Ù. ±×¸®³ª, ¿©ÀüÈ÷
¾²±â Àü¿¡ XOR ¿¬»êÀ» ÇØ¾ß Çϱ⠶§¹®¿¡ ¾²±â ¼º´ÉÀº
¹Ì·¯¸µ¸¸Å »¡¶óÁú¼ö ¾ø´Ù. Àб⠿ª½Ã ¿©·¯°³ÀÇ µ¥ÀÌÅÍ°¡
ÀÖ´Â °ÍÀÌ ¾Æ´Ï±â ¶§¹®¿¡ ¹Ì·¯¸µ ¸¸Å »¡¶óÁú ¼ö ¾ø´Ù.
avoids the write-bottleneck of RAID-4 by alternately
storing the parity stripe on each of the drives.
However, write performance is still not as good as for
mirroring, as the parity stripe must still be read and
XOR'ed before it is written. Read performance is also
not as good as it is for mirroring, as, after all, there
is only one copy of the data, not two or more. RAID-5's
principle advantage over mirroring is that it offers
redundancy and protection against single-drive failure,
while offering far more storage capacity when used with
three or more drives.
o RAID-2 ¿Í RAID-3 ´Â ÀÌÁ¦ °ÅÀÇ »ç¿ëµÇÁö ¾Ê´Â´Ù. ¸î¸î
·¹º§Àº Çö´ë µð½ºÅ© ±â¼ú·Î ÀÎÇØ ÇÊ¿ä ¾ø¾îÁ³±â ¶§¹®ÀÌ´Ù.
RAID-2´Â RAID-4¿Í ºñ½ÁÇÏÁö¸¸, parity ´ë½Å¿¡ ECC Á¤º¸¸¦
ÀúÀåÇÏ´Â °ÍÀÌ ´Ù¸£´Ù. ÇöÀçÀÇ ¸ðµç µð½ºÅ©µéÀº ECC Á¤º¸¸¦
µð½ºÅ© ÀÚü³»¿¡ ³Ö¾î¹ö·È´Ù. ÀÌ°ÍÀº, µð½ºÅ© ÀÚü¿¡ ÀÛÀº
¾ÈÀüÀåÄ¡¸¦ ´Ü °ÍÀÌ´Ù. RAID-2 ´Â µð½ºÅ© ¾²±â µµÁß
Àü¿ø°ø±ÞÀÌ Â÷´ÜµÉ ¶§, µ¥ÀÌÅÍ ¾ÈÀü¼ºÀ» Á¦°øÇØÁØ´Ù.
ÇÏÁö¸¸, ¹èÅ͸® ¹é¾÷À̳ª, clean shutdown ¿ª½Ã ¶È°°Àº
±â´ÉÀ» Á¦°øÇÑ´Ù.. RAID-3Àº °¡´ÉÇÑ ÃÖ¼ÒÀÇ stripe Å©±â¸¦
»ç¿ëÇÏ´Â °ÍÀ» Á¦¿ÜÇϸé RAID-4 ¿Í ºñ½ÁÇÏ´Ù. Linux
¼ÒÇÁÆ®¿þ¾î RAID µå¶óÀ̹ö´Â RAID-2 ¿Í RAID-3¸¦ ¸ðµÎ
Áö¿øÇÏÁö ¾Ê´Â´Ù.
are seldom used anymore, and to some degree are have been
made obsolete by modern disk technology. RAID-2 is
similar to RAID-4, but stores ECC information instead of
parity. Since all modern disk drives incorporate ECC
under the covers, this offers little additional
protection. RAID-2 can offer greater data consistency if
power is lost during a write; however, battery backup and
a clean shutdown can offer the same benefits. RAID-3 is
similar to RAID-4, except that it uses the smallest
possible stripe size. As a result, any given read will
involve all disks, making overlapping I/O requests
difficult/impossible. In order to avoid delay due to
rotational latency, RAID-3 requires that all disk drive
spindles be synchronized. Most modern disk drives lack
spindle-synchronization ability, or, if capable of it,
lack the needed connectors, cables, and manufacturer
documentation. Neither RAID-2 nor RAID-3 are supported
by the Linux Software-RAID drivers.
o ±×¿ÜÀÇ RAID ·¹º§µéÀº ´Ù¾çÇÑ ¼ö¿ä¿Í ÆǸÅÀڵ鿡 ÀÇÇØ
¸¸µé¾îÁ³°í, Ưº°ÇÑ Çϵå¿þ¾î¸¦ ÇÊ¿ä·Î Çϰųª ¾î¶² °ÍµéÀº
ÀúÀÛ±ÇÀ» º¸È£ ¹Þ°í ÀÖ´Ù. Linux ¼ÒÇÁÆ®¿þ¾î RAID´Â ´Ù¸¥
¾î¶² º¯Á¾µéµµ Áö¿øÇÏÁö ¾Ê´Â´Ù.
have been defined by various researchers and vendors.
Many of these represent the layering of one type of raid
on top of another. Some require special hardware, and
others are protected by patent. There is no commonly
accepted naming scheme for these other levels. Sometime
the advantages of these other systems are minor, or at
least not apparent until the system is highly stressed.
Except for the layering of RAID-1 over RAID-0/linear,
Linux Software RAID does not support any of the other
variations.
3. ¼³Ä¡¿Í ¼³Á¤
1. Q: Software RAID ¸¦ ¾î¶»°Ô ¼³Ä¡ÇØ¾ß °¡Àå ÁÁÀ» ±î¿ä?
A: ³ª´Â ÆÄÀÏ ½Ã½ºÅÛ °èȹÀÌ Á» ´õ ¾î·Á¿î À¯´Ð½º ¼³Á¤ÀÛ¾÷ÀÎ
°ÍÀ» ±ú´Ý µµ·Ï ³²°ÜµÐ´Ù. Áú¹®¿¡ ´ëÇÑ ´ë´äÀ¸·Î, ¿ì¸®°¡ ÇÑ
ÀÏÀ» ¼³¸íÇÏ°Ú´Ù. ¿ì¸®´Â °¢°¢ 2.1 ±â°¡ÀÇ EIDE µð½ºÅ©¸¦
¾Æ·¡¿Í °°ÀÌ ¼³Á¤ÇÒ °èȹÀ» ¼¼¿ü´Ù.
I keep rediscovering that file-system planning is one of the
more difficult Unix configuration tasks. To answer your
question, I can describe what we did.
We planned the following setup:
o two EIDE disks, 2.1.gig each.
disk partition mount pt. size device
1 1 / 300M /dev/hda1
1 2 swap 64M /dev/hda2
1 3 /home 800M /dev/hda3
1 4 /var 900M /dev/hda4
2 1 /root 300M /dev/hdc1
2 2 swap 64M /dev/hdc2
2 3 /home 800M /dev/hdc3
2 4 /var 900M /dev/hdc4
o °¢ µð½ºÅ©´Â ¸ðµÎ ºÐ¸®µÈ ÄÁÆ®·Ñ·¯¿Í ¸®º» ÄÉÀÌºí »ó¿¡ ÀÖ´Ù.
ÀÌ°ÍÀº ÇϳªÀÇ ÄÁÆ®·Ñ·¯³ª ÄÉÀ̺íÀÌ °íÀå ³µÀ» ¶§,
µð½ºÅ©µéÀÌ °°ÀÌ »ç¿ë ºÒ°¡´ÉÇÏ°Ô µÇ´Â °ÍÀ» ¸·¾ÆÁØ´Ù.
Each disk is on a separate controller (& ribbon cable).
The theory is that a controller failure and/or ribbon
failure won't disable both disks. Also, we might
possibly get a performance boost from parallel operations
over two controllers/cables.
o ·çÆ® ÆÄƼ¼Ç (/ /dev/hda1 )¿¡ ¸®´ª½º Ä¿³ÎÀ» ¼³Ä¡ÇÒ °ÍÀÌ´Ù.
ÀÌ ÆÄƼ¼ÇÀ» bootable·Î ¼³Á¤Çضó.
Install the Linux kernel on the root (/) partition
/dev/hda1. Mark this partition as bootable.
o /dev/hac1Àº /dev/hda1 ÀÇ RAID º¹»çº»ÀÌ ¾Æ´Ñ ´Ü¼ø
º¹»çº»ÀÌ´Ù. ÀÌ°ÍÀ¸·Î, ù¹ø° µð½ºÅ©°¡ ¿À·ù³µÀ» ¶§ rescue
µð½ºÅ©¸¦ »ç¿ëÇØ ÀÌ ÆÄƼ¼ÇÀ» bootable ¼³Á¤ÇÏ¿© ½Ã½ºÅÛÀ»
´Ù½Ã ÀνºÅçÇÏÁö ¾Ê°í »ç¿ëÇÒ ¼ö ÀÖ´Ù.
/dev/hdc1 will contain a ``cold'' copy of /dev/hda1. This
is NOT a raid copy, just a plain old copy-copy. It's
there just in case the first disk fails; we can use a
rescue disk, mark /dev/hdc1 as bootable, and use that to
keep going without having to reinstall the system. You
may even want to put /dev/hdc1's copy of the kernel into
LILO to simplify booting in case of failure.
ÀÌ°ÍÀº ½É°¢ÇÑ ¹®Á¦ ¹ß»ý½Ã, raid superblock-corruption
À̳ª ´Ù¸¥ ÀÌÇØÇÒ¼ö ¾ø´Â ¹®Á¦¿¡ ´ëÇÑ °ÆÁ¤¾øÀÌ ½Ã½ºÅÛÀ»
ºÎÆÃÇÒ ¼ö ÀÖ°Ô ÇØÁØ´Ù.
The theory here is that in case of severe failure, I can
still boot the system without worrying about raid
superblock-corruption or other raid failure modes &
gotchas that I don't understand.
o /dev/hda3 ¿Í /dev/hdc3 ´Â ¹Ì·¯¸µÀ» ÅëÇØ /dev/md0 °¡
µÉ°ÍÀÌ´Ù.
/dev/hda3 and /dev/hdc3 will be mirrors /dev/md0.
o /dev/hda4 ¿Í /dev/hdc4 ´Â ¹Ì·¯¸µÀ» ÅëÇØ /dev/md1 °¡
µÉ°ÍÀÌ´Ù.
/dev/hda4 and /dev/hdc4 will be mirrors /dev/md1.
o ¿ì¸®´Â ¾Æ·¡¿Í °°Àº ÀÌÀ¯·Î ÆÄƼ¼ÇÀ» ³ª´©°í, /var ¿Í /home
ÆÄƼ¼ÇÀ» ¹Ì·¯¸µÇϱâ·Î °áÁ¤ÇÏ¿´´Ù.
we picked /var and /home to be mirrored, and in separate
partitions, using the following logic:
o / (·çÆ® ÆÄƼ¼Ç)ÀÇ µ¥ÀÌÅ͵éÀº »ó´ëÀûÀ¸·Î Àß º¯ÇÏÁö ¾Ê´Â´Ù.
/ (the root partition) will contain relatively static,
non-changing data: for all practical purposes, it will be
read-only without actually being marked & mounted read-
only.
o /home ÆÄƼ¼ÇÀº ''õõÈ÷'' º¯ÇÏ´Â µ¥ÀÌÅ͸¦ °¡Áö°í ÀÖ´Ù.
/home will contain ''slowly'' changing data.
o /var> ´Â ¸ÞÀÏ spool , µ¥ÀÌÅͺ£À̽º ³»¿ë, À¥ ¼¹öÀÇ log ¿Í
°°Àº ±Þ¼ÓÈ÷ º¯ÇÏ´Â µ¥ÀÌÅ͸¦ Æ÷ÇÔÇÏ°í ÀÖ´Ù.
/var will contain rapidly changing data, including mail
spools, database contents and web server logs.
ÀÌ·¸°Ô ¿©·¯°³ÀÇ ´Ù¸¥ ÆÄƼ¼ÇÀ» ³ª´©´Â °ÍÀº, Àΰ£ÀÇ ½Ç¼ö,
Àü¿ø, ȤÀº osÀÇ ¹®Á¦µîÀÌ ÀϾÀ» ¶§, ±×°ÍÀÌ ¹ÌÄ¡´Â
¿µÇâÀÌ ÇϳªÀÇ ÆÄƼ¼Ç¿¡¸¸ ÇÑÁ¤µÇ±â ¶§¹®ÀÌ´Ù.
The idea behind using multiple, distinct partitions is
that if, for some bizarre reason, whether it is human
error, power loss, or an operating system gone wild,
corruption is limited to one partition. In one typical
case, power is lost while the system is writing to disk.
This will almost certainly lead to a corrupted
filesystem, which will be repaired by fsck during the
next boot. Although fsck does it's best to make the
repairs without creating additional damage during those
repairs, it can be comforting to know that any such
damage has been limited to one partition. In another
typical case, the sysadmin makes a mistake during rescue
operations, leading to erased or destroyed data.
Partitions can help limit the repercussions of the
operator's errors.
o /usr ¿Í /opt ÆÄƼ¼ÇÀ» ¼±ÅÃÇÏ¿©µµ ±¦Âú¾ÒÀ» °ÍÀÌ´Ù. »ç½Ç,
Çϵ尡 Á»´õ ÀÖ¾ú´Ù¸é, /opt ¿Í /home ÆÄƼ¼ÇÀ» RAID-5 ·Î
¼³Á¤ÇÏ´Â °ÍÀÌ ´õ ÁÁ¾ÒÀ» °ÍÀÌ´Ù. ÁÖÀÇÇÒ Á¡Àº /usr
ÆÄƼ¼ÇÀ» RAID-5·Î ¼³Á¤ÇÏÁö ¸»¶ó´Â °ÍÀÌ´Ù. ½É°¢ÇÑ ¹®Á¦°¡
ÀϾÀ» °æ¿ì /usr ÆÄƼ¼Ç¿¡ ¸¶¿îÆ® ÇÒ¼ö ¾ø°Ô µÉ °ÍÀÌ°í,
/usr ÆÄƼ¼Ç¾ÈÀÇ ³×Æ®¿öÅ© Åø°ú ÄÄÆÄÀÏ·¯ °°Àº °ÍµéÀ» ÇÊ¿ä·Î
ÇÏ°Ô µÉ °ÍÀÌ´Ù. RAID-1À» »ç¿ëÇÑ´Ù¸é, ÀÌ·± ¿¡·¯°¡ ³µÀ»¶§,
RAID´Â »ç¿ëÇÒ¼ö ¾ø¾îµµ µÎ°³ÀÇ ¹Ì·¯¸µµÈ °ÍÁß Çϳª¿¡´Â
¸¶¿îÆ®°¡ °¡´ÉÇÏ´Ù.
Other reasonable choices for partitions might be /usr or
/opt. In fact, /opt and /home make great choices for
RAID-5 partitions, if we had more disks. A word of
caution: DO NOT put /usr in a RAID-5 partition. If a
serious fault occurs, you may find that you cannot mount
/usr, and that you want some of the tools on it (e.g. the
networking tools, or the compiler.) With RAID-1, if a
fault has occurred, and you can't get RAID to work, you
can at least mount one of the two mirrors. You can't do
this with any of the other RAID levels (RAID-5, striping,
or linear append).
±×·¡¼ Áú¹®¿¡ ´ëÇÑ ¿Ï¼ºµÈ ´äÀº:
o ù¹ø° µð½ºÅ©ÀÇ Ã¹¹ø° ÆÄƼ¼Ç¿¡ ¿î¿µÃ¼Á¦¸¦ ¼³Ä¡ÇÏ°í ´Ù¸¥
ÆÄƼ¼ÇµéÀº ¸¶¿îÆ®ÇÏÁö ¸»¾Æ¶ó.
install the OS on disk 1, partition 1. do NOT mount any
of the other partitions.
o ¸í·É´ÜÀ§·Î RAID¸¦ ¼³Ä¡Ç϶ó.
install RAID per instructions.
o md0 ¿Í md1. ¼³Á¤Ç϶ó.
configure md0 and md1.
o µð½ºÅ© ¿À·ù°¡ ÀϾÀ» ¶§ ¹«¾ùÀ» ÇØ¾ß ÇÏ´Â Áö ÁغñÇضó.
°ü¸®ÀÚ°¡ Áö±Ý ½Ç¼öÇÏ´ÂÁö ã¾Æº¸°í, Ÿ°ÝÀ» ÀÔ°Ô ³öµÎÁö
¸¶¶ó. ±×¸®°í °æÇèÀ» ½×¾Æ¶ó. (¿ì¸®´Â µð½ºÅ©°¡ ÀÛµ¿ÇÏ°í
ÀÖ´Â µ¿¾È, Àü¿øÀ» ²¨º¸¾Ò´Ù. ÀÌ°ÍÀº ¸ÛûÇغ¸ÀÌÁö¸¸,
Á¤º¸¸¦ ¾òÀ» ¼ö ÀÖ´Ù.)
convince yourself that you know what to do in case of a
disk failure! Discover sysadmin mistakes now, and not
during an actual crisis. Experiment! (we turned off
power during disk activity -- this proved to be ugly but
informative).
o /var ¸¦ /dev/md1À¸·Î ¿Å±â´Â Áß, ¾î´À Á¤µµ À߸øµÈ
mount/copy/unmount/rename/reboot À» Çغ¸¶ó. Á¶½ÉÈ÷¸¸
ÇÑ´Ù¸é, À§ÇèÇÏÁö´Â ¾ÊÀ» °ÍÀÌ´Ù.
do some ugly mount/copy/unmount/rename/reboot scheme to
move /var over to the /dev/md1. Done carefully, this is
not dangerous.
o ±×¸®°í, ±×°ÍµéÀ» Áñ°Ü¶ó.
2. Q: mdadd, mdrun µîÀÇ ¸í·É°ú raidadd, raidrun ¸í·ÉÀÇ ´Ù¸¥ Á¡ÀÌ
¹º°¡¿ä?
A: raidtools ÆÐÅ°ÁöÀÇ 0.5 ¹öÁ¯ºÎÅÍ À̸§ÀÌ ¹Ù²î¾ú´Ù. md·Î
À̸§ÀÌ ºÙ´Â °ÍÀº 0.43 ÀÌÀü¹öÁ¯ÀÌ°í raid·Î À̸§ÀÌ ºÙ´Â °ÍÀº
0.5 ¹öÁ¯°ú ´õ »õ¹öÁ¯µéÀÌ´Ù..
The names of the tools have changed as of the 0.5 release of
the raidtools package. The md naming convention was used in
the 0.43 and older versions, while raid is used in 0.5 and
newer versions.
3. Q: °¡Áö°í ÀÖ´Â 2.0.34 Ä¿³Î¿¡¼ RAID-linear ¿Í RAID-0 ¸¦ »ç¿ëÇÏ°í
½Í´Ù. RAID-linear ¿Í RAID-0 À» À§Çؼ ÆÐÄ¡°¡ ÇÊ¿äÇÏÁö ¾Ê±â ¶§¹®¿¡.
raid ÆÐÄ¡´Â ÇÏ°í ½ÍÁö ¾Ê´Ù. ¾îµð¿¡ °¡¸é, À̰͵éÀ» À§ÇÑ raid-tool À»
±¸ÇÒ¼ö ÀÖ³ª?
A: °ú°ÜÇÑ Áú¹®ÀÌ´Ù. »ç½Ç, ÃÖ½ÅÀÇ raid toolµéÀº ÄÄÆÄÀÏ Çϱâ
À§ÇØ RAID-1,4,5 Ä¿³Î ÆÐÄ¡¸¦ ÇÊ¿ä·Î ÇÑ´Ù. ÇöÀç raid toolÀÇ
ÄÄÆÄÀÏµÈ ¹ÙÀ̳ʸ® ¹öÁ¯Ã£Áö ¸øÇß´Ù. ÇÏÁö¸¸, 2.1.100 Ä¿³Î¿¡¼
ÄÄÆÄÀÏµÈ ¹ÙÀ̳ʸ®°¡ 2.0.34 Ä¿³Î¿¡¼ RAID-0/linear ÆÄƼ¼ÇÀ»
¸¸µå´Â °ÍÀ» Àß ¼öÇàÇÏ´Â °ÍÀ» º¸¾Ò´Ù. ±×·¡¼, ³ª´Â
http://linas.org/linux/Software-RAID/ ¿¡ mdadd,mdcreateµîÀÇ
¹ÙÀ̳ʸ®¸¦ ÀÓ½ÃÀûÀ¸·Î ¿Ã¸°´Ù.
This is a tough question, indeed, as the newest raid tools
package needs to have the RAID-1,4,5 kernel patches
installed in order to compile. I am not aware of any pre-
compiled, binary version of the raid tools that is available
at this time. However, experiments show that the raid-tools
binaries, when compiled against kernel 2.1.100, seem to work
just fine in creating a RAID-0/linear partition under
2.0.34. A brave soul has asked for these, and I've
temporarily placed the binaries mdadd, mdcreate, etc. at
http://linas.org/linux/Software-RAID/ You must get the man
pages, etc. from the usual raid-tools package.
4. Q: ·çÆ® ÆÄƼ¼Ç¿¡ RAID¸¦ Àû¿ëÇÒ ¼ö Àִ°¡? ¿Ö md µð½ºÅ©·Î Á÷Á¢
ºÎÆÃÇÒ ¼ö ¾ø´Â°¡?
A:
LILO¿Í Loadlin ¸ðµÎ RAID ÆÄƼ¼Ç¿¡¼ Ä¿³ÎÀ̹ÌÁö¸¦ Àоî¿Ã ¼ö
¾ø´Ù. ·çÆ® ÆÄƼ¼Ç¿¡ RAID¸¦ Àû¿ëÇÏ°í ½Í´Ù¸é, Ä¿³ÎÀ» ÀúÀåÇÒ
RAID°¡ ¾Æ´Ñ ÆÄƼ¼ÇÀ» ¸¸µé¾î¾ß ÇÒ°ÍÀÌ´Ù. (ÀϹÝÀûÀ¸·Î ÀÌ
ÆÄƼ¼ÇÀÇ À̸§Àº /bootÀÌ´Ù.) <HarryH@Royal.Net> ·ÎºÎÅÍ ¹ÞÀº
initial ramdisk (initrd) ¶Ç´Â, ÆÐÄ¡´Â RAID µð½ºÅ©¸¦ root
µð¹ÙÀ̽º·Î »ç¿ë°¡´ÉÇÏ°Ô ÇØ ÁÙ°ÍÀÌ´Ù. (ÀÌ ÆÐÄ¡´Â ÃÖ±Ù
2.1.xÄ¿³Î¿¡´Â ±âº»ÀûÀ¸·Î äÅõǾîÀÖ´Ù.)
Both LILO and Loadlin need an non-stripped/mirrored
partition to read the kernel image from. If you want to
strip/mirror the root partition (/), then you'll want to
create an unstriped/mirrored partition to hold the
kernel(s). Typically, this partition is named /boot. Then
you either use the initial ramdisk support (initrd), or
patches from Harald Hoyer <HarryH@Royal.Net> that allow a
stripped partition to be used as the root device. (These
patches are now a standard part of recent 2.1.x kernels)
°Å±â¿¡´Â »ç¿ëÇÒ ¼ö ÀÖ´Â ¸î°¡Áö ¹æ¹ýÀÌ Àִµ¥, Çϳª´Â
Bootable RAID mini-HOWTO:
<ftp://ftp.bizsystems.com/pub/raid/bootable-raid>¿¡ ÀÚ¼¼È÷
¼³¸íµÇ¾î ÀÖ´Ù.
There are several approaches that can be used. One approach
is documented in detail in the Bootable RAID mini-HOWTO:
<ftp://ftp.bizsystems.com/pub/raid/bootable-raid>.
¶Ç´Â, ¾Æ·¡Ã³·³ mkinitrd ¸¦ »ç¿ëÇØ ramdisk image¸¦ ¸¸µé¼öµµ
ÀÖ´Ù.
Alternately, use mkinitrd to build the ramdisk image, see
below.
Edward Welbon <welbon@bga.com> writes:
o ... all that is needed is a script to manage the boot
setup. To mount an md filesystem as root, the main thing
is to build an initial file system image that has the
needed modules and md tools to start md. I have a simple
script that does this.
o For boot media, I have a small cheap SCSI disk (170MB I
got it used for $20). This disk runs on a AHA1452, but
it could just as well be an inexpensive IDE disk on the
native IDE. The disk need not be very fast since it is
mainly for boot.
o This disk has a small file system which contains the
kernel and the file system image for initrd. The initial
file system image has just enough stuff to allow me to
load the raid SCSI device driver module and start the
raid partition that will become root. I then do an
echo 0x900 > /proc/sys/kernel/real-root-dev
(0x900 is for /dev/md0) and exit linuxrc. The boot proceeds
normally from there.
o I have built most support as a module except for the
AHA1452 driver that brings in the initrd filesystem. So
I have a fairly small kernel. The method is perfectly
reliable, I have been doing this since before 2.1.26 and
have never had a problem that I could not easily recover
from. The file systems even survived several 2.1.4[45]
hard crashes with no real problems.
o At one time I had partitioned the raid disks so that the
initial cylinders of the first raid disk held the kernel
and the initial cylinders of the second raid disk hold
the initial file system image, instead I made the initial
cylinders of the raid disks swap since they are the
fastest cylinders (why waste them on boot?).
o The nice thing about having an inexpensive device
dedicated to boot is that it is easy to boot from and can
also serve as a rescue disk if necessary. If you are
interested, you can take a look at the script that builds
my initial ram disk image and then runs LILO.
<http://www.realtime.net/~welbon/initrd.md.tar.gz>
It is current enough to show the picture. It isn't espe
cially pretty and it could certainly build a much smaller
filesystem image for the initial ram disk. It would be easy
to a make it more efficient. But it uses LILO as is. If
you make any improvements, please forward a copy to me. 8-)
5. Q: striping À§¿¡ ¹Ì·¯¸µÀÌ °¡´ÉÇÏ´Ù°í µé¾ú´Âµ¥, »ç½ÇÀΰ¡? loopback
ÀåÄ¡·Î ¹Ì·¯¸µÇÒ ¼ö Àִ°¡?
A: ±×·¸´Ù. ÇÏÁö¸¸, ±× ¹Ý´ë·Î´Â ¾ÈµÈ´Ù.
Yes, but not the reverse. That is, you can put a stripe
over several disks, and then build a mirror on top of this.
However, striping cannot be put on top of mirroring.
°£´ÜÈ÷ ±â¼úÀûÀÎ ¼³¸íÀ» µ¡ºÙÀÌÀÚ¸é, linear ¿Í stripe´Â
ÀÚüÀûÀ¸·Î ll_rw_blk ·çƾÀ» »ç¿ëÇÏ´Â µ¥ ÀÌ°ÍÀº block ¸¦
»ç¿ëÇÏÁö ¾Ê°í µð½ºÅ© device¿Í sector¸¦ »ç¿ëÇØ Á¤½ÄÀûÀ¸·Î,
±×¸®°í Àú¼öÁØÀÇ access¸¦ ÇÑ´Ù, ¶§¹®¿¡, ´Ù¸¥ ¹Ì·¯¸µÀ§¿¡
À§Ä¡½Ãų¼ö ¾ø´Ù.
A brief technical explanation is that the linear and stripe
personalities use the ll_rw_blk routine for access. The
ll_rw_blk routine maps disk devices and sectors, not
blocks. Block devices can be layered one on top of the
other; but devices that do raw, low-level disk accesses,
such as ll_rw_blk, cannot.
ÇöÀç (1997³â 11¿ù) RAID´Â loopback device¸¦ Áö¿øÇÏÁö ¾ÊÁö¸¸,
°ð Áö¿øÇÒ °ÍÀÌ´Ù.
Currently (November 1997) RAID cannot be run over the
loopback devices, although this should be fixed shortly.
6. Q: µÎ°³ÀÇ ÀÛÀº µð½ºÅ©¿Í ¼¼°³ÀÇ Å« µð½ºÅ©¸¦ °¡Áö°í ÀÖÀ»¶§, ÀÛÀº
µð½ºÅ© µÎ°³¸¦ RAID-0À¸·Î ¹Àº ÈÄ, ³ª¸ÓÁö µð½ºÅ©µé°ú, RAID-5¸¦
¸¸µé¼ö Àִ°¡?
A: 1997³â 11¿ù ÇöÀç, RAID-5·Î ¹À» ¼ö´Â ¾ø´Ù. ¹¿©Áø
µð½ºÅ©µé·Î´Â RAID-1(¹Ì·¯¸µ)¸¸ °¡´ÉÇÏ´Ù.
Currently (November 1997), for a RAID-5 array, no.
Currently, one can do this only for a RAID-1 on top of the
concatenated drives.
7. Q: µÎ°³ÀÇ µð½ºÅ©·Î RAID-1 À» ¼³Á¤ÇÏ´Â °Í°ú, RAID-5¸¦ ¼³Á¤ÇÏ´Â °ÍÀÌ
¾î¶»°Ô ´Ù¸¥°¡?
A: µ¥ÀÌÅÍÀÇ ÀúÀåÀ²¿¡´Â Â÷ÀÌ°¡ ¾ø´Ù. µð½ºÅ©¸¦ ´õ ºÙÈù´Ù°í
ÀúÀåÀ²ÀÌ ´Ã¾î°¡´Â °Íµµ ¾Æ´Ï´Ù.
There is no difference in storage capacity. Nor can disks
be added to either array to increase capacity (see the
question below for details).
RAID-1 Àº °¢ µå¶óÀ̺꿡¼ µÎ ¼½Å͸¦ µ¿½Ã¿¡ Àд ºÐ»ê ±â¼úÀ»
»ç¿ëÇϱ⠶§¹®¿¡ µÎ¹èÀÇ Àб⠼º´ÉÀ» º¸¿©ÁØ´Ù.
RAID-1 offers a performance advantage for reads: the RAID-1
driver uses distributed-read technology to simultaneously
read two sectors, one from each drive, thus doubling read
performance.
RAID-5´Â ¸¹Àº °ÍµéÀ» Æ÷ÇÔÇÏÁö¸¸, 1997³â 9¿ù ÇöÀç ±îÁö´Â,
µ¥ÀÌÅÍ µð½ºÅ©°¡ parity µð½ºÅ©·Î ½ÇÁ¦ÀûÀ¸·Î ¹Ì·¯¸µµÇÁö´Â
¾Ê´Â´Ù. ¶§¹®¿¡ µ¥ÀÌÅ͸¦ º´·Ä·Î ÀÐÁö´Â ¾Ê´Â´Ù.
The RAID-5 driver, although it contains many optimizations,
does not currently (September 1997) realize that the parity
disk is actually a mirrored copy of the data disk. Thus, it
serializes data reads.
8. Q:
µÎ°³ÀÇ µð½ºÅ©°¡ ¸Á°¡Á³À»¶§¿¡´Â ¾î¶»°Ô ´ëºñÇÏÁÒ?
A: ¸î¸îÀÇ RAID ´Â ¾Ë°í¸®ÁòÀº ¿©·¯°³ÀÇ µð½ºÅ©°¡ ¸Á°¡Á³À» ¶§¸¦
´ëºñÇÒ ¼ö ÀÖ´Ù. ÇÏÁö¸¸, ÇöÀç ¸®´ª½º¿¡¼ Áö¿øµÇÁö´Â ¾Ê´Â´Ù.
±×·¯³ª, RAIDÀ§¿¡ RAID¸¦ ±¸ÃàÇÔÀ¸·Î½á, Linux Software
RAID·Îµµ, ±×·± »óȲ¿¡ ´ëºñÇÒ ¼ö ÀÖ´Ù. ¿¹¸¦ µé¸é,9°³ÀÇ
µð½ºÅ©·Î 3°³ÀÇ RAID-5¸¦ ¸¸µé°í ´Ù½Ã ±×°ÍÀ» ÇϳªÀÇ RAID-5 ·Î
¸¸µå´Â °ÍÀÌ´Ù. ÀÌ·± ¼³Á¤Àº 3°³ÀÇ µð½ºÅ©°¡ ¸Á°¡Á³À»¶§±îÁö
´ëºñÇÒ ¼ö ÀÖÁö¸¸, ¸¹Àº °ø°£ÀÌ ''³¶ºñ''µÈ´Ù´Â °ÍÀ» ÁÖ¸ñÇ϶ó.
Some of the RAID algorithms do guard against multiple disk
failures, but these are not currently implemented for Linux.
However, the Linux Software RAID can guard against multiple
disk failures by layering an array on top of an array. For
example, nine disks can be used to create three raid-5
arrays. Then these three arrays can in turn be hooked
together into a single RAID-5 array on top. In fact, this
kind of a configuration will guard against a three-disk
failure. Note that a large amount of disk space is
''wasted'' on the redundancy information.
For an NxN raid-5 array,
N=3, 5 out of 9 disks are used for parity (=55%)
N=4, 7 out of 16 disks
N=5, 9 out of 25 disks
...
N=9, 17 out of 81 disks (=~20%)
ÀϹÝÀûÀ¸·Î, MxN °³·Î ¸¸µé¾îÁø RAID¸¦ À§ÇØ M+N-1 °³ÀÇ
µð½ºÅ©°¡ parity ·Î »ç¿ëµÇ°í, M = N À϶§ ¹ö·ÁÁö´Â ¾çÀÌ ÃÖ¼Ò°¡
µÉ °ÍÀÌ´Ù.
In general, an MxN array will use M+N-1 disks for parity.
The least amount of space is "wasted" when M=N.
´Ù¸¥ ¹æ¹ýÀº ¼¼°³ÀÇ µð½ºÅ©(RAID-5·Î ¼³Á¤µÈ)·Î RAID-1À» ¸¸µå´Â
°ÍÀÌ´Ù. ±×°ÍÀº, ¼¼°³ÀÇ µð½ºÅ©Áß °°Àº µ¥ÀÌÅ͸¦ °¡Áö´Â 2/3À»
³¶ºñÇÏ°Ô µÉ °ÍÀÌ´Ù.
Another alternative is to create a RAID-1 array with three
disks. Note that since all three disks contain identical
data, that 2/3's of the space is ''wasted''.
9. Q: ÆÄƼ¼ÇÀÌ Á¦´ë·Î unmount µÇÁö ¾Ê¾ÒÀ» ¶§ fsck°¡ ½ÇÇàµÇ¾î¼
ÆÄÀϽýºÅÛÀ» ½º½º·Î °íÄ¡´Â °ÍÀÌ ¾î¶»°Ô °¡´ÉÇÑÁö ¾Ë°í ½Í´Ù. RAID
½Ã½ºÅÛÀ» ckraid --fix ·Î °íÄ¥¼ö Àִµ¥ ¿Ö ±×°ÍÀ» ÀÚµ¿À¸·Î ÇÏÁö
¾Ê´Â°¡?
I'd like to understand how it'd be possible to have something like
fsck: if the partition hasn't been cleanly unmounted, fsck runs and
fixes the filesystem by itself more than 90% of the time. Since the
machine is capable of fixing it by itself with ckraid --fix, why
not make it automatic?
A: /etc/rc.d/rc.sysinit ¿¡ ¾Æ·¡¿Í °°ÀÌ Ãß°¡ÇÔÀ¸·Î½á ÇÒ¼ö
ÀÖ´Ù.
This can be done by adding lines like the following to
/etc/rc.d/rc.sysinit:
mdadd /dev/md0 /dev/hda1 /dev/hdc1 || {
ckraid --fix /etc/raid.usr.conf
mdadd /dev/md0 /dev/hda1 /dev/hdc1
}
or
mdrun -p1 /dev/md0
if [ $? -gt 0 ] ; then
ckraid --fix /etc/raid1.conf
mdrun -p1 /dev/md0
fi
Á»´õ ¿Ïº®ÇÑ ½ºÅ©¸³Æ®¸¦ ¸¸µé±â ÀÌÀü¿¡ ½Ã½ºÅÛÀÌ ¾î¶»°Ô ÄÑÁö´ÂÁö º¸µµ·Ï
ÇÏÀÚ.
Before presenting a more complete and reliable script, lets review the
theory of operation.
Á¤»óÀûÀ¸·Î Á¾·áµÇÁö ¾Ê¾Ò´Ù¸é, ¸®´ª½º´Â ¾Æ·¡¿Í °°Àº »óÅÂÁßÀÇ ÇϳªÀÏ
²¨¶ó°í Gadi OxmanÀº ¸»Çß´Ù.
Gadi Oxman writes: In an unclean shutdown, Linux might be in one of
the following states:
o ºñÁ¤»ó Á¾·á´ç½Ã, ¸Þ¸ð¸®ÀÇ µð½ºÅ© ij½¬°¡ ÀúÀå(sync) µÈ »óÅÂ.
µ¥ÀÌÅÍ´Â ¼Õ»óµÇÁö ¾Ê´Â´Ù.
The in-memory disk cache was in sync with the RAID set when the
unclean shutdown occurred; no data was lost.
o ¹®Á¦°¡ ¹ß»ýÇßÀ» ¶§, µð½ºÅ© ij½¬´Â RAID ¿¡ ÀÖ´Â °Íº¸´Ù ÃÖ±Ù °ÍÀ̾ú´ø
»óÅ ÀÌ °á°ú´Â ÆÄÀϽýºÅÛÀÌ ¸Á°¡Áö°í, µ¥ÀÌÅ͸¦ ÀÒÀ» °ÍÀÌ´Ù. ÀÌ°ÍÀº
´Ù½Ã ¾Æ·¡ÀÇ µÎ°¡Áö »óÅ·Π³ª»´Ù.
The in-memory disk cache was newer than the RAID set contents when
the crash occurred; this results in a corrupted filesystem and
potentially in data loss.
This state can be further divided to the following two states:
o ¸®´ª½º°¡ µ¥ÀÌÅ͸¦ ¾²°í(write) ÀÖ¾úÀ» °æ¿ì.
o ¸®´ª½º°¡ µ¥ÀÌÅ͸¦ ¾²°í ÀÖÁö ¾Ê¾ÒÀ» °æ¿ì.
RAID-1À» »ç¿ëÇÑ´Ù¸é, À§ÀÇ Ã¹¹ø° °æ¿ì¿¡¼, ¾î´ÀÁ¤µµ¸¸ ¹Ì·¯¸µµÆÀ»
°æ¿ì°¡ »ý±ä´Ù. ÀÌ·± °æ¿ì, ´ÙÀ½ ºÎÆö§, ¹Ì·¯¸µµÈ µ¥ÀÌÅÍ°¡ ¼·Î °°Áö
¾ÊÀ» °ÍÀÌ´Ù.
ÀÌ·±°æ¿ì¿¡ ¹Ì·¯¸µÀÌ ´Ù¸¥°É ¹«½ÃÇÑ´Ù¸é, Àбâ½Ã ¹Ì·¯¸µµÈ °ÍÁß Çϳª¸¦
¼±ÅÃÇÒ °ÍÀÌ°í, ¸ð¼øµÈ °á°ú¸¦ Ãâ·ÂÇÒ °ÍÀÌ´Ù.
Suppose we were using a RAID-1 array. In (2a), it might happen that
before the crash, a small number of data blocks were successfully
written only to some of the mirrors, so that on the next reboot,
the mirrors will no longer contain the same data.
If we were to ignore the mirror differences, the raidtools-0.36.3
read-balancing code might choose to read the above data blocks from
any of the mirrors, which will result in inconsistent behavior (for
example, the output of e2fsck -n /dev/md0 can differ from run to
run).
RAID ´Â ºñÁ¤»óÀûÀÎ shutdownÀ» À§ÇØ ¼³°èµÈ °ÍÀÌ ¾Æ´Ï°í, ÀϹÝÀûÀ¸·Î
¹Ì·¯¸µµÈ µ¥ÀÌÅÍ°¡ ´Ù¸¦ ¶§³ª, ÆÄÀϽýºÅÛÀÌ °íÀå³µÀ» ¶§ÀÇ ¿Ïº®ÇÑ
ÇØ°áÃ¥µµ ¾ø´Ù.
Since RAID doesn't protect against unclean shutdowns, usually there
isn't any ''obviously correct'' way to fix the mirror differences
and the filesystem corruption.
For example, by default ckraid --fix will choose the first
operational mirror and update the other mirrors with its contents.
However, depending on the exact timing at the crash, the data on
another mirror might be more recent, and we might want to use it as
the source mirror instead, or perhaps use another method for
recovery.
¾Æ·¡ÀÇ ½ºÅ©¸³Æ®¸¦ rc.raid.init ¿¡ Ãß°¡ÇÏ°í, ±× µð·ºÅ丮¿¡ path¸¦
°É¾î¶ó. ±×°ÍÀº Á»´õ ¾ÈÀüÇÑ ºÎÆÃÀ» Áö¿øÇÒ °ÍÀÌ°í, ƯÈ÷, ÀÏÄ¡ÇÏÁö
¾Ê´Â µð½ºÅ©³ª, ÄÜÆ®·Ñ·¯, ÄÜÆ®·Ñ·¯ µå¶óÀ̹öµîÀÌ ÀÖÀ¸¸é, Áú°í
¹Ýº¹ÀûÀ¸·Î chraid¸¦ ½ÇÇàÇÒ °ÍÀÌ´Ù. rc.raid.init´Â fsck·Î
·çÆ®ÆÄƼ¼ÇÀÌ Ã¼Å©µÇ°í Read Write ¸¶¿îÆ® µÈ »óÅ¿¡¼ ÀÛµ¿ÇÒ °ÍÀÌ´Ù.
The following script provides one of the more robust boot-up
sequences. In particular, it guards against long, repeated
ckraid's in the presence of uncooperative disks, controllers, or
controller device drivers. Modify it to reflect your config, and
copy it to rc.raid.init. Then invoke rc.raid.init after the root
partition has been fsck'ed and mounted rw, but before the remaining
partitions are fsck'ed. Make sure the current directory is in the
search path.
mdadd /dev/md0 /dev/hda1 /dev/hdc1 || {
rm -f /fastboot # force an fsck to occur
ckraid --fix /etc/raid.usr.conf
mdadd /dev/md0 /dev/hda1 /dev/hdc1
}
# if a crash occurs later in the boot process,
# we at least want to leave this md in a clean state.
/sbin/mdstop /dev/md0
mdadd /dev/md1 /dev/hda2 /dev/hdc2 || {
rm -f /fastboot # force an fsck to occur
ckraid --fix /etc/raid.home.conf
mdadd /dev/md1 /dev/hda2 /dev/hdc2
}
# if a crash occurs later in the boot process,
# we at least want to leave this md in a clean state.
/sbin/mdstop /dev/md1
mdadd /dev/md0 /dev/hda1 /dev/hdc1
mdrun -p1 /dev/md0
if [ $? -gt 0 ] ; then
rm -f /fastboot # force an fsck to occur
ckraid --fix /etc/raid.usr.conf
mdrun -p1 /dev/md0
fi
# if a crash occurs later in the boot process,
# we at least want to leave this md in a clean state.
/sbin/mdstop /dev/md0
mdadd /dev/md1 /dev/hda2 /dev/hdc2
mdrun -p1 /dev/md1
if [ $? -gt 0 ] ; then
rm -f /fastboot # force an fsck to occur
ckraid --fix /etc/raid.home.conf
mdrun -p1 /dev/md1
fi
# if a crash occurs later in the boot process,
# we at least want to leave this md in a clean state.
/sbin/mdstop /dev/md1
# OK, just blast through the md commands now. If there were
# errors, the above checks should have fixed things up.
/sbin/mdadd /dev/md0 /dev/hda1 /dev/hdc1
/sbin/mdrun -p1 /dev/md0
/sbin/mdadd /dev/md12 /dev/hda2 /dev/hdc2
/sbin/mdrun -p1 /dev/md1
¾Æ·¡¿Í °°ÀÌ rc.raid.halt¸¦ Ãß°¡ÇÏ°í ½Í´Ù¸é Ãß°¡Ç϶ó.
In addition to the above, you'll want to create a rc.raid.halt which
should look like the following:
/sbin/mdstop /dev/md0
/sbin/mdstop /dev/md1
rc.sysinit¿Í init.d/halt ½ºÅ©¸³¤¼Áß ½Ã½ºÅÛÀÇ halt/roboot¸¦ À§ÇÑ ¸ðµç
unmount Àü¿¡ À§ ÆÄÀÏÀ» ÷ºÎ½ÃÄѶó. ( rc.sysinit¿¡´Â fsck°¡
½ÇÆÐÇßÀ»¶§, µð½ºÅ©¸¦ unmount ÇÏ°í reboot ÇÏ´Â ·çƾÀÌ ÀÖ´Ù.)
Be sure to modify both rc.sysinit and init.d/halt to include this
everywhere that filesystems get unmounted before a halt/reboot. (Note
that rc.sysinit unmounts and reboots if fsck returned with an error.)
10.
Q: ÇöÀç °¡Áø ÇϳªÀÇ µð½ºÅ©·Î ¹ÝÂÊÂ¥¸® RAID-1À» ±¸¼ºÈÄ, ³ªÁß¿¡
µð½ºÅ©¸¦ Ãß°¡ÇÒ¼ö ÀÖ³ª¿ä?
A: ÇöÀçÀÇ µµ±¸µé·Î´Â ºÒ°¡´ÉÇÏ°í, ¾î¶² ½¬¿î ¹æ¹ýµµ ¾ø´Ù.
ƯÈ÷, µð½ºÅ©ÀÇ ³»¿ëÀ» ´ÜÁö º¹»çÇÔÀ¸·Î½á, ¹Ì·¯¸µÀº ÀÌ·ç¾îÁöÁö
¾Ê´Â´Ù. RAID µå¶óÀ̹ö´Â ÇÇƼ¼Ç³¡ÀÇ ÀÛÀº °ø°£À» superblock·Î
»ç¿ëÇϱ⠶§¹®ÀÌ´Ù. ÀÌ°ÍÀº ÀÛÀº °ø°£¸¸À» Â÷ÁöÇÏÁö¸¸, À̹Ì
Á¸ÀçÇÏ´Â ÆÄÀÏ ½Ã½ºÅ׿¡ ´Ü¼øÈ÷ º¹»çÇÏ·Á ÇÒ°æ¿ì, superblockÀº
ÆÄÀÏ ½Ã½ºÅÛÀ» µ¤¾î¾º¿ï °ÍÀÌ°í, µ¥ÀÌÅ͸¦ ¾û¸ÁÀ¸·Î ¸¸µé°ÍÀÌ´Ù.
ext2fs ÆÄÀϽýºÅÛÀº ÆÄÀϵéÀÌ Á¶°¢³ª´Â °ÍÀ» ¸·±âÀ§ÇØ,
ÆÄÀϵéÀ» ¹«ÀÛÀ§·Î ¹èÄ¡½ÃÄѿԱ⠶§¹®¿¡, µð½ºÅ©¸¦ ¸ðµÎ
»ç¿ëÇϱâ Àü¿¡, ÆÄƼ¼ÇÀÇ ³¡ºÎºÐÀÌ ÃæºÐÈ÷ »ç¿ëµÉ ¼ö ÀÖ´Ù.
With the current tools, no, not in any easy way. In
particular, you cannot just copy the contents of one disk
onto another, and then pair them up. This is because the
RAID drivers use glob of space at the end of the partition
to store the superblock. This decreases the amount of space
available to the file system slightly; if you just naively
try to force a RAID-1 arrangement onto a partition with an
existing filesystem, the raid superblock will overwrite a
portion of the file system and mangle data. Since the
ext2fs filesystem scatters files randomly throughput the
partition (in order to avoid fragmentation), there is a very
good chance that some file will land at the very end of a
partition long before the disk is full.
´ç½ÅÀÌ À¯´ÉÇÏ´Ù¸é, superblockÀÌ ¾î´ÀÁ¤µµÀÇ °ø°£À» Â÷ÁöÇÏ´ÂÁö
°è»êÇؼ, ÆÄÀϽýºÅÛÀ» Á¶±Ý ÀÛ°Ô ¸¸µé°ÍÀ» Á¦¾ÈÇÑ´Ù. ±×¸®°í,
µð½ºÅ©¸¦ Ãß°¡ÇÒ¶§, RAID ÅøÀ» ´ç½Å¿¡ ¸Â°Ô °íÃļ »ç¿ëÇؾß
ÇÒ°ÍÀÌ´Ù. (±× ÅøµéÀÌ ²ûÂïÇÏ°Ô º¹ÀâÇÏÁö´Â ¾Ê´Ù.)
If you are clever, I suppose you can calculate how much room
the RAID superblock will need, and make your filesystem
slightly smaller, leaving room for it when you add it later.
But then, if you are this clever, you should also be able to
modify the tools to do this automatically for you. (The
tools are not terribly complex).
ÁÖÀDZí°Ô ÀÐÀº »ç¶÷À̶ó¸é, ¾Æ·¡¿Í °°Àº °ÍÀÌ ÀÛµ¿ÇÒ°ÍÀ̶ó°í
ÁöÀûÇßÀ» °ÍÀÌ´Ù. ³ª´Â ÀÌ°ÍÀ» ½ÃµµÇغ¸°Å³ª Áõ¸íÇغ¸Áö´Â
¸øÇß´Ù. /dev/nullÀ» ÇϳªÀÇ ±â±â·Î½á mkraid¿¡ ÀÌ¿ëÇÏ´Â
°ÍÀÌ´Ù. ÁøÂ¥ µð½ºÅ© Çϳª¸¦ °¡Áö°í mdadd -r ¸¦ ½ÇÇà½ÃŲÈÄ,
mkraid·Î RAID ¹è¿À» ¸¸µé¼ö ÀÖÀ» °ÍÀÌ°í, µð½ºÅ© Çϳª°¡
±úÁ³À» ¶§Ã³·³ "degraded" ¸ðµå·Î ÀÛµ¿½Ãų¼ö ÀÖÀ»°ÍÀÌ´Ù.
Note:A careful reader has pointed out that the following
trick may work; I have not tried or verified this: Do the
mkraid with /dev/null as one of the devices. Then mdadd -r
with only the single, true disk (do not mdadd /dev/null).
The mkraid should have successfully built the raid array,
while the mdadd step just forces the system to run in
"degraded" mode, as if one of the disks had failed.
4. ¿¡·¯ÀÇ º¹±¸
1. Q:
RAID-1À» »ç¿ëÇÏ°í Àִµ¥, µð½ºÅ©°¡ ÀÛµ¿Áß Àü¿øÀÌ ²¨Á³½À´Ï´Ù.
¾î¶»°Ô ÇØ¾ß ÇÒ±î¿ä?
A: ÀÌ·± »óȲ¿¡¼´Â ¸î°¡Áö ¹æ¹ýÀÌ ÀÖ´Ù.
The redundancy of RAID levels is designed to protect against
a disk failure, not against a power failure.
There are several ways to recover from this situation.
o ù¹ø° ¹æ¹ýÀº raid µµ±¸µéÀ» »ç¿ëÇÏ´Â °ÍÀÌ´Ù. ÀÌ°ÍÀº
raidÀÇ µ¥ÀÌÅ͵éÀ» µ¿±âÈ ½ÃÄÑÁØ´Ù.(sync) ÇÏÁö¸¸,
ÆÄÀϽýºÅÛÀÇ ¼Õ»óÀº º¹±¸ÇØÁÖÁö ¾ÊÀ¸¹Ç·Î ÈÄ¿¡ fsck¸¦
»ç¿ëÇØ °íÃÄ¾ß ÇÑ´Ù. RAID ´Â ckraid /etc/raid1.conf ÅëÇØ
Á¡°ËÇغ¼¼ö ÀÖ´Ù.(RAID-1ÀÏ °æ¿ìÀÌ´Ù, ´Ù¸¥ °æ¿ì¶ó¸é,
/etc/raid5.confó·³»ç¿ëÇØ¾ß ÇÑ´Ù.) ckraid
/etc/raid1.conf --fix ¸¦ »ç¿ëÇØ RAIDµÈ µð½ºÅ©Áß Çϳª¸¦
¼±ÅÃÇؼ, ´Ù¸¥ µð½ºÅ©·Î ¹Ì·¯¸µ ½Ãų¼ö ÀÖ´Ù. µð½ºÅ©Áß
¾î´À °ÍÀ» ¼±ÅÃÇØ¾ß ÇÒÁö ¸ð¸¥´Ù¸é, ckraid /etc/raid1.conf
--fix --force-source /dev/hdc3 ÀÌ·± ½ÄÀ¸·Î --force-
source¿É¼ÇÀ» »ç¿ëÇ϶ó.
ckraid ´Â --fix ¿É¼ÇÀ» Á¦°ÅÇÔÀ¸·Î½á RAID ½Ã½ºÅÛ¿¡ ¾î¶²
º¯È¾øÀÌ ¾ÈÀüÇÏ°Ô ½Ãµµ µÉ ¼ö ÀÖ´Ù. Á¦¾ÈµÈ º¯°æ¿¡ ´ëÇؼ,
¸¸Á·ÇÒ °æ¿ì¿¡ --fix ¿É¼ÇÀ» »ç¿ëÇضó.
Method (1): Use the raid tools. These can be used to
sync the raid arrays. They do not fix file-system
damage; after the raid arrays are sync'ed, then the file-
system still has to be fixed with fsck. Raid arrays can
be checked with ckraid /etc/raid1.conf (for RAID-1, else,
/etc/raid5.conf, etc.)
Calling ckraid /etc/raid1.conf --fix will pick one of the
disks in the array (usually the first), and use that as
the master copy, and copy its blocks to the others in the
mirror.
To designate which of the disks should be used as the
master, you can use the --force-source flag: for example,
ckraid /etc/raid1.conf --fix --force-source /dev/hdc3
The ckraid command can be safely run without the --fix
option to verify the inactive RAID array without making
any changes. When you are comfortable with the proposed
changes, supply the --fix option.
o µÎ¹ø° ¹æ¹ýÀº ù¹ø° ¹æ¹ýº¸´Ù ¸¹ÀÌ ÁÁÀº ¹æ¹ýÀº ¾Æ´Ï´Ù.
/dev/hda3 ¿Í /dev/hdc3 ·Î ¸¸µé¾îÁø RAID-1 µð½ºÅ©°¡ ÀÖ´Ù°í
°¡Á¤ÇÒ¶§, ¾Æ·¡¿Í °°ÀÌ Çغ¼¼ö ÀÖ´Ù.
Method (2): Paranoid, time-consuming, not much better
than the first way. Lets assume a two-disk RAID-1 array,
consisting of partitions /dev/hda3 and /dev/hdc3. You
can try the following:
a. fsck /dev/hda3
b. fsck /dev/hdc3
c. µÎ°³ÀÇ ÆÄƼ¼ÇÁß, ¿¡·¯°¡ ÀûÀº ÂÊÀ̳ª, ´õ ½±°Ô º¹±¸°¡
µÈÂÊ, ¶Ç´Â º¹±¸ÇÏ°í ½ÍÀº µ¥ÀÌÅÍ°¡ ³²¾ÆÀÖ´Â Âʵî,
»õ·Î¿î ¸¶½ºÅÍ·Î ¾µ ÆÄƼ¼ÇÀ» °áÁ¤ÇØ¾ß ÇÑ´Ù. /dev/hdc3
¸¦ ¼±ÅÃÇß´Ù ÇÏÀÚ.
decide which of the two partitions had fewer errors,
or were more easily recovered, or recovered the data
that you wanted. Pick one, either one, to be your new
``master'' copy. Say you picked /dev/hdc3.
d. dd if=/dev/hdc3 of=/dev/hda3
e. mkraid raid1.conf -f --only-superblock
¸¶Áö¸· µÎ´Ü°è ´ë½Å¿¡ ckraid /etc/raid1.conf --fix
--force-source /dev/hdc3 ¸¦ »ç¿ëÇϸé Á» ´õ ºü¸¦ °ÍÀÌ´Ù.
Instead of the last two steps, you can instead run ckraid
/etc/raid1.conf --fix --force-source /dev/hdc3 which
should be a bit faster.
o ¼¼¹ø¤ ¹æ¹ýÀº ¿À·¨µ¿¾È fsck¸¦ ±â´Ù¸®±â°¡ ±ÍÂúÀº »ç¶÷µéÀ»
À§ÇÑ °ÍÀÌ´Ù. ù¹ø° 3´Ü°è¸¦ ¶Ù¾î³Ñ°í ¹Ù·Î ¸¶Áö¸·
µÎ´Ü°è¸¦ ½ÇÇàÇÏ´Â °ÍÀÌ´Ù. ±×·± ÈÄ¿¡ fsck /dev/md0 ¸¦
½ÇÇàÇÏ´Â °ÍÀÌ´Ù. ÀÌ°ÍÀº ù¹ø° ¹æ¹ýÀÇ ¸ð¾çÀ» ¹Ù²Û °ÍÀÏ
»ÓÀÌ´Ù.
Method (3): Lazy man's version of above. If you don't
want to wait for long fsck's to complete, it is perfectly
fine to skip the first three steps above, and move
directly to the last two steps. Just be sure to run fsck
/dev/md0 after you are done. Method (3) is actually just
method (1) in disguise.
¾î¶² ¹æ¹ýµµ RAID¸¦ µ¿±âÈ ½ÃÄÑÁÙ ¼ö ÀÖÀ» »ÓÀÌ°í, ÆÄÀÏ
½Ã½ºÅÛ ¶ÇÇÑ Àß º¹±¸µÇ±â¸¦ ¿øÇÒ °ÍÀÌ´Ù. À̸¦ À§Çؼ,
fsck¸¦ md device¸¦ unmount ½ÃŲÈÄ fsck¸¦ ½ÇÇàÇ϶ó.
In any case, the above steps will only sync up the raid
arrays. The file system probably needs fixing as well:
for this, fsck needs to be run on the active, unmounted
md device.
¼¼°³ÀÇ µð½ºÅ©·Î ±¸¼ºµÈ RAID-1 ½Ã½ºÅÛÀ̶ó¸é ¸¹ÀÌ ÀÏÄ¡ÇÑ
ºÎºÐÀ» ÅëÇØ, ´äÀ» ã¾Æ³»´Â ¹æ¹ýµîÀÇ, Á¶±Ý ´õ ¸¹Àº ¹æ¹ýÀÌ
ÀÖ°ÚÁö¸¸, ÀÌ·± °ÍÀ» ÀÚµ¿À¸·Î ÇØÁÖ´Â µµ±¸´Â ÇöÀç Áö¿øµÇÁö
¾Ê´Â´Ù.
With a three-disk RAID-1 array, there are more
possibilities, such as using two disks to ''vote'' a
majority answer. Tools to automate this do not currently
(September 97) exist.
2. Q: RAID-4 ¶Ç´Â RAID-5 ½Ã½ºÅÛÀ» °¡Áö°í Àִµ¥, µð½ºÅ© ÀÛµ¿Áß¿¡
²¨Á³½À´Ï´Ù. ¾î¶»°Ô ÇØ¾ß ÇÒ±î¿ä?
A: RAID-4³ª RAID-5 ½Ã½ºÅÛ¿¡¼´Â ¿¹ºñ ¼ö¸®¸¦ À§ÇØ fsck¸¦
»ç¿ëÇÒ ¼ö ¾ø´Ù. ¸ÕÀú ckraid¸¦ »ç¿ëÇ϶ó.
ckraid ´Â --fix ¿É¼ÇÀ» Á¦°ÅÇÔÀ¸·Î½á RAID ½Ã½ºÅÛ¿¡ ¾î¶²
º¯È¾øÀÌ ¾ÈÀüÇÏ°Ô ½Ãµµ µÉ ¼ö ÀÖ´Ù. Á¦¾ÈµÈ º¯°æ¿¡ ´ëÇؼ,
¸¸Á·ÇÒ °æ¿ì¿¡ --fix ¿É¼ÇÀ» »ç¿ëÇضó.
¿øÇÑ´Ù¸é,--suggest-failed-disk-mask ¿É¼ÇÀ» ÅëÇØ µð½ºÅ©µéÁß
Çϳª¸¦ ¸Á°¡Áø µð½ºÅ©·Î ÁöÁ¤ÇÑ Ã¤ ckraid¸¦ ½Ãµµ ÇÒ¼ö ÀÖ´Ù.
RAID-5´Â ´ÜÁö ÇϳªÀÇ bit¸¸ÀÌ flag ·Î ¼³Á¤µÇ¾î Àֱ⠶§¹®¿¡,
RAID-5´Â µÎ°³ÀÇ µð½ºÅ©°¡ ¸Á°¡Á³À» ¶§´Â º¹±¸ÇÒ ¼ö ¾ø´Ù.
¾Æ·¡´Â binary bit mask ÀÌ´Ù.
The redundancy of RAID levels is designed to protect against
a disk failure, not against a power failure.
Since the disks in a RAID-4 or RAID-5 array do not contain a
file system that fsck can read, there are fewer repair
options. You cannot use fsck to do preliminary checking
and/or repair; you must use ckraid first.
The ckraid command can be safely run without the --fix
option to verify the inactive RAID array without making any
changes. When you are comfortable with the proposed
changes, supply the --fix option.
If you wish, you can try designating one of the disks as a
''failed disk''. Do this with the --suggest-failed-disk-
mask flag.
Only one bit should be set in the flag: RAID-5 cannot
recover two failed disks. The mask is a binary bit mask:
thus:
0x1 == first disk
0x2 == second disk
0x4 == third disk
0x8 == fourth disk, etc.
¶Ç´Â, --suggest-fix-parity ¿É¼ÇÀ» ÅëÇØ parity ¼½Å͸¦ ¼öÁ¤ÇÒ
¼öµµ ÀÖ´Ù. ÀÌ°ÍÀº ´Ù¸¥ ¼½Å͵é·ÎºÎÅÍ parity ¸¦ ´Ù½Ã
°è»êÇس¾ °ÍÀÌ´Ù.
--suggest-failed-dsk-mask ¿Í --suggest-fix-parity ¿É¼ÇÀº
--fix¿É¼ÇÀ» Á¦°ÅÇÔÀ¸·Î½á, °¡´ÉÇÑ ¼öÁ¤ °èȹÀÇ È®ÀÎÀ» À§ÇØ
¾ÈÀüÇÏ°Ô »ç¿ëµÉ¼ö ÀÖ´Ù.
Alternately, you can choose to modify the parity sectors, by
using the --suggest-fix-parity flag. This will recompute
the parity from the other sectors.
The flags --suggest-failed-dsk-mask and --suggest-fix-parity
can be safely used for verification. No changes are made if
the --fix flag is not specified. Thus, you can experiment
with different possible repair schemes.
3. Q: /dev/hda3 °ú /dev/hdc3 µÎ°³ÀÇ µð½ºÅ©·Î /dev/md0 ÀÇ RAID-1
½Ã½ºÅÛÀ» ¸¸µé¾î¼ »ç¿ëÇÏ°í ÀÖ½À´Ï´Ù. ÃÖ±Ù¿¡, /dev/hdc3 ÀÌ °íÀ峪¼
»õ µð½ºÅ©¸¦ ±¸ÀÔÇß´Ù. Á¦ °¡Àå Ä£ÇÑ Ä£±¸°¡, ''dd if=/dev/hda3
of=/dev/hdc3''¸¦ Çغ¸¶ó°í Çؼ Çغ¸¾ÒÁö¸¸, ¾ÆÁ÷µµ ÀÛµ¿ÇÏ°í ÀÖÁö
¾Ê½À´Ï´Ù.
My RAID-1 device, /dev/md0 consists of two hard drive partitions:
/dev/hda3 and /dev/hdc3. Recently, the disk with /dev/hdc3 failed,
and was replaced with a new disk. My best friend, who doesn't
understand RAID, said that the correct thing to do now is to ''dd
if=/dev/hda3 of=/dev/hdc3''. I tried this, but things still don't
work.
A: Ä£±¸¸¦ ´ç½ÅÀÇ ÄÄÇ»ÅÍ¿¡ °¡±îÀÌ °¡°Ô ÇÏÁö ¾Ê°Ô Çؼ,
±³¿ì°ü°è¸¦ À¯ÁöÇÏ´Â °Ô ÁÁÀ» °ÍÀÌ´Ù. ´ÙÇེ·´°Ôµµ, ½É°¢ÇÑ
¼Õ»óÀ» ÀÔÁö´Â ¾Ê´Â´Ù. ¾Æ·¡¿Í °°ÀÌ ½ÇÇàÇÔÀ¸·Î½á, ½Ã½ºÅÛÀ»
ȸº¹½Ãų¼ö ÀÖÀ» °ÍÀÌ´Ù.
mkraid raid1.conf -f --only-superblock
dd ¸í·É¾î¸¦ ÀÌ¿ëÇؼ, ÆÄƼ¼ÇÀÇ º¹»çº»À» ¸¸µå´Â °ÍÀº ´ëºÎºÐ
°¡´ÉÇÏ´Ù. ÇÏÁö¸¸, RAID-1 ½Ã½ºÅÛ¿¡¼´Â superblock ÀÌ ´Ù¸£±â
¶§¹®¿¡ ¾ÈµÈ´Ù. ¶§¹®¿¡ RAID-1À» µÎ ÆÄƼ¼ÇÁßÀÇ ÇϳªÀÇ
superblock¸¦ ´Ù½Ã ¸¸µé¾îÁÖ¸é, ´Ù½Ã »ç¿ë°¡´ÉÇÏ°Ô µÉ °ÍÀÌ´Ù.
You should keep your best friend away from you computer.
Fortunately, no serious damage has been done. You can
recover from this by running:
mkraid raid1.conf -f --only-superblock
By using dd, two identical copies of the partition were cre
ated. This is almost correct, except that the RAID-1 kernel
extension expects the RAID superblocks to be different.
Thus, when you try to reactivate RAID, the software will
notice the problem, and deactivate one of the two parti
tions. By re-creating the superblock, you should have a
fully usable system.
4. Q: ³» mkraid ´Â --only-superblock ¿É¼ÇÀÌ Áö¿øµÇÁö ¾Ê´Â ¹öÁ¯ÀÔ´Ï´Ù.
¾î¶»°Ô ÇØ¾ß ÇÒ±î¿ä?
A: »õ·Î¿î Åø¿¡¼´Â --force-resync ¿É¼ÇÀ¸·Î ¹Ù²ã¾ú°í, ÃÖ½ÅÀÇ
ÅøµéÀÇ »ç¿ëÀº ¾Æ·¡¿Í °°ÀÌ »ç¿ëÇØ¾ß ÇÑ´Ù.
umount /web (/dev/md0°¡ ¸¶¿îÆ® µÇ¾îÀÖ´Â °÷.)
raidstop /dev/md0
mkraid /dev/md0 --force-resync --really-force
raidstart /dev/md0
cat /proc/mdstat ¸¦ ÅëÇØ °á°ú¸¦ º¼ ¼ö ÀÖÀ» °ÍÀÌ°í, mount
/dev/md0¸¦ ÅëÇØ ´Ù½Ã »ç¿ë°¡´ÉÇÒ °ÍÀÌ´Ù.
The newer tools drop support for this flag, replacing it
with the --force-resync flag. It has been reported that the
following sequence appears to work with the latest tools and
software:
umount /web (where /dev/md0 was mounted on)
raidstop /dev/md0
mkraid /dev/md0 --force-resync --really-force
raidstart /dev/md0
After doing this, a cat /proc/mdstat should report resync in
progress, and one should be able to mount /dev/md0 at this
point.
5. Q: /dev/hda3 °ú /dev/hdc3 µÎ°³ÀÇ µð½ºÅ©·Î /dev/md0 ÀÇ RAID-1
½Ã½ºÅÛÀ» ¸¸µé¾î¼ »ç¿ëÇÏ°í ÀÖ½À´Ï´Ù. Á¦ °¡Àå Ä£ÇÑ (¿©ÀÚ?) Ä£±¸°¡,
¸øº¸´Â »çÀÌ, /dev/hda3 ¸¦ fsck ·Î ½ÇÇà½ÃÅ°´Â ¹Ù¶÷¿¡, RAID°¡
µ¿ÀÛÇÏÁö ¾Ê°í ÀÖ½À´Ï´Ù. ¾î¶»°Ô ÇØ¾ß ÇÒ±î¿ä?
My RAID-1 device, /dev/md0 consists of two hard drive partitions:
/dev/hda3 and /dev/hdc3. My best (girl?)friend, who doesn't
understand RAID, ran fsck on /dev/hda3 while I wasn't looking, and
now the RAID won't work. What should I do?
A: ´ç½ÅÀº °¡Àå Ä£ÇÑ Ä£±¸¶ó´Â °³³äÀ» ´Ù½Ã Çѹø »ý°¢Çغ¸¾Æ¾ß
ÇÒ°ÍÀÌ´Ù. ÀϹÝÀûÀ¸·Î fsck ´Â RAID¸¦ ¸¸µå´Â ÆÄƼ¼ÇÁß
Çϳª¿¡¼ µ¹·Á¼´Â Àý´ë·Î ¾ÈµÈ´Ù. ÆÄƼ¼Ç ¼Õ»óÀ̳ª, µ¥ÀÌÅÍ
¼Õ»óÀÌ ¹ß»ýµÇÁö ¾Ê¾Ò´Ù°í ÇÑ´Ù¸é, RAID-1 ½Ã½ºÅÛÀ» ¾Æ·¡¿Í °°ÀÌ
¼ö¸®ÇÒ ¼ö ÀÖ´Ù.
a. /dev/hda3 ÀÇ ¹é¾÷À» ¹Þ´Â´Ù.
b. dd if=/dev/hda3 of=/dev/hdc3
c. mkraid raid1.conf -f --only-superblock
You should re-examine your concept of ``best friend''. In general,
fsck should never be run on the individual partitions that compose a
RAID array. Assuming that neither of the partitions are/were heavily
damaged, no data loss has occurred, and the RAID-1 device can be
recovered as follows:
a. make a backup of the file system on /dev/hda3
b. dd if=/dev/hda3 of=/dev/hdc3
c. mkraid raid1.conf -f --only-superblock
This should leave you with a working disk mirror.
6. Q:
¿Ö À§ÀÇ º¹±¸ ¼ø¼´ë·Î ÇØ¾ß Çϴ°¡?
A: RAID-1 À» ÀÌ·ç´Â ÆÄƼ¼ÇµéÀº ¿Ïº®È÷ °°Àº º¹Á¦º»À̾î¾ß Çϱâ
¶§¹®ÀÌ´Ù. ¹Ì·¯¸µÀÌ ÀÛµ¿µÇÁö ¾ÊÀ» °æ¿ì, ÇÇƼ¼ÇµéÁß Çϳª¸¦
RAID¸¦ »ç¿ëÇÏÁö ¾Ê°í mountÇؼ »ç¿ëÇÏ°í, ¾Æ·¡¿Í °°Àº ¸í·ÉÀ»
»ç¿ëÇØ RAID ½Ã½ºÅÛÀ» º¹±¸ÇÑ ÈÄ, ÆÄƼ¼ÇÀ» unmount ÇÏ°í, RAID
½Ã½ºÅÛÀ» ´Ù½Ã ½ÃÀÛÇÏ¿©¾ß ÇÑ´Ù. ¾Æ·¡ÀÇ ¸í·ÉµéÀº RAID-1ÀÌ
¾Æ´Ñ ´Ù¸¥ ·¹º§µé¿¡ »ç¿ëÇÏ¸é ¾ÈµÈ´Ù´Â °ÍÀ» ÁÖÀÇÇ϶ó.
Because each of the component partitions in a RAID-1 mirror
is a perfectly valid copy of the file system. In a pinch,
mirroring can be disabled, and one of the partitions can be
mounted and safely run as an ordinary, non-RAID file system.
When you are ready to restart using RAID-1, then unmount the
partition, and follow the above instructions to restore the
mirror. Note that the above works ONLY for RAID-1, and not
for any of the other levels.
À§¿¡¼ ó·³ ¸Á°¡ÁöÁö ¾ÊÀº ÆÄƼ¼ÇÀ» ¸Á°¡Áø ÆÄƼ¼ÇÀ¸·Î
º¹»çÇÏ´Â °ÍÀº ±âºÐ ÁÁÀº ÀÏÀÏ °ÍÀÌ´Ù. ÀÌÁ¦ md ÀåÄ¡¸¦ fsck ·Î
°Ë»çÇϱ⸸ ÇÏ¸é µÈ´Ù.
It may make you feel more comfortable to reverse the
direction of the copy above: copy from the disk that was
untouched to the one that was. Just be sure to fsck the
final md.
7. Q: ³ª´Â À§ÀÇ Áú¹®µé¿¡ È¥¶õ½º·´´Ù. fsck /dev/md0 ¸¦ ½ÇÇàÇÏ´Â °ÍÀº
¾ÈÀüÇÑ°¡?
A: ±×·¸´Ù. md ÀåÄ¡µéÀ» fsck ÇÏ´Â °ÍÀº ¾ÈÀüÇÏ´Ù. »ç½Ç, ±×°Ô
¾ÈÀüÇÏ°Ô fsck¸¦ ½ÇÇà½ÃÅ°´Â À¯ÀÏÇÑ ¹æ¹ýÀÌ´Ù.
Yes, it is safe to run fsck on the md devices. In fact,
this is the only safe place to run fsck.
8. Q: µð½ºÅ©°¡ õõÈ÷ ¿À·ù³ª±â ½ÃÀÛÇÑ´Ù¸é, ¾î´À ÆÄƼ¼ÇÀÇ ¿À·ùÀÎÁö
¸í¹éÇÒ°ÍÀΰ¡? ÀÌ·± È¥¶õÀº °ü¸®ÀڷκÎÅÍ À§ÇèÇÑ °áÁ¤À» ³»¸®°Ô ÇÒ
¼öµµ ÀÖÁö ¾ÊÀº°¡.
A: µð½ºÅ©¿¡ ¹®Á¦°¡ »ý±â±â »õÀÛÇϸé, RAIDÀÇ Àú¼öÁØ µå¶óÀ̹ö°¡
error Äڵ带 ¹ÝȯÇÒ °ÍÀÌ´Ù. RAID µå¶óÀ̹ö´Â ÁÁÀº ÂÊ diskÀÇ
superblock¾È¿¡ ''bad'' Ç¥½Ã¸¦ ÇÒ°ÍÀÌ°í, °¡´ÉÇÑ ¹Ì·¯¸µÀ»
À¯ÁöÇϵµ·Ï ¸í·ÉÇÒ °ÍÀÌ´Ù. (³ªÁß¿¡ ¾î¶² ¹Ì·¯¸µÀÌ ÁÁÀº ÂÊÀÌ°í
³ª»ÛÂÊÀÎÁö ¹è¿ì°Ô µÉ °ÍÀÌ´Ù.) ¹°·Ð, disk¿Í Àú¼öÁØ
µå¶óÀ̹ö°¡ Àбâ/¾²±â ¿¡·¯¸¦ °¨ÁöÇÒ °ÍÀÌ°í, Á¶¿ëÈ÷ µ¥ÀÌÅÍ°¡
¸Á°¡ÁöÁö´Â ¾Ê´Â´Ù.
Once a disk fails, an error code will be returned from the
low level driver to the RAID driver. The RAID driver will
mark it as ``bad'' in the RAID superblocks of the ``good''
disks (so we will later know which mirrors are good and
which aren't), and continue RAID operation on the remaining
operational mirrors.
This, of course, assumes that the disk and the low level
driver can detect a read/write error, and will not silently
corrupt data, for example. This is true of current drives
(error detection schemes are being used internally), and is
the basis of RAID operation.
9. Q:
hot-repair ´Â ¹«¾ùÀΰ¡?
A: RAID ½Ã½ºÅÛÁß ÇϳªÀÇ µð½ºÅ©°¡ ¸Á°¡Á³À» ¶§, RAIDÀÇ
ÁߴܾøÀÌ ½ÇÇàÁß¿¡ ¿©ºÐÀÇ µð½ºÅ©ÀÇ Ãß°¡¸¦ ÅëÇØ º¹±¸ÇÏ´Â
±×·¯³ª ÀÌ°ÍÀ» »ç¿ëÇϱâ À§Çؼ±, ¿©ºÐÀÇ µð½ºÅ©´Â ºÎÆýÃ
¼±¾ðµÇ¾ú°Å³ª. ¸î¸î Ưº°ÇÑ Àåºñ°¡ Áö¿øÇÏ´Â Àü¿øÀÌ µé¾î¿Â
»óÅ¿¡¼ Çϵ带 Ãß°¡°¡ °¡´ÉÇØ¾ß ÇÑ´Ù.
Work is underway to complete ``hot reconstruction''. With
this feature, one can add several ``spare'' disks to the
RAID set (be it level 1 or 4/5), and once a disk fails, it
will be reconstructed on one of the spare disks in run time,
without ever needing to shut down the array.
However, to use this feature, the spare disk must have been
declared at boot time, or it must be hot-added, which
requires the use of special cabinets and connectors that
allow a disk to be added while the electrical power is on.
97³â 10¿ù MDÀÇ º£Å¸¹öÁ¯ÀÌ ÇÒ¼ö ÀÖ´Â °ÍÀº ¾Æ·¡¿Í °°´Ù.
o ¿©ºÐÀÇ µð½ºÅ©¸¦ ÅëÇÑ RAID 1 ¿Í 5 ÀÇ º¹±¸
o À߸øµÈ ½Ã½ºÅÛÁ¾·á½Ã RAID-5 parity ÀÇ º¹±¸
o ÀÛµ¿ÇÏ´Â RAID 1, 4,5 ½Ã½ºÅÛ¿¡ ¿©ºÐ µå¶óÀ̺ê Ãß°¡.
ÇöÀç ±âº»ÀûÀ¸·Î ÀÚµ¿º¹±¸´Â ¼³Á¤µÇ¾î ÀÖÁö ¾Ê°í,
include/linux/md.h ¾ÈÀÇ SUPPORT_RECONSTRUCTION °ªÀ»
¹Ù²Ù¾î ¼³Á¤ÇÒ ¼ö ÀÖ´Ù.
As of October 97, there is a beta version of MD that
allows:
o RAID 1 and 5 reconstruction on spare drives
o RAID-5 parity reconstruction after an unclean shutdown
o spare disk to be hot-added to an already running RAID 1
or 4/5 array
By default, automatic reconstruction is (Dec 97)
currently disabled by default, due to the preliminary
nature of this work. It can be enabled by changing the
value of SUPPORT_RECONSTRUCTION in include/linux/md.h.
Ä¿³Î ±â¹ÝÀÇ º¹±¸°¡ ¼³Á¤µÇ¾î ÀÖ°í, RAID ½Ã½ºÅÛ¿¡ ¿©ºÐÀÇ
µð½ºÅ©( superblockÀº ÀÌ¹Ì mkraid¸¦ ÅëÇØ ¸¸µé¾îÁ³À»
°ÍÀÌ´Ù.) ¸¦ Ãß°¡ÇÏ·Á ÇÑ´Ù¸é, Ä¿³ÎÀº ³»¿ëÀ» ÀÚµ¿ÀûÀ¸·Î
º¹±¸½ÃÄÑÁÙ °ÍÀÌ´Ù. (ÀϹÝÀûÀÎ mdstop, µð½ºÅ©±³Ã¼, ckraid,
mdrun ÀÇ ÀýÂ÷¸¦ ¹âÁö ¾Ê¾Æµµ µÈ´Ù.)
If spare drives were configured into the array when it
was created and kernel-based reconstruction is enabled,
the spare drive will already contain a RAID superblock
(written by mkraid), and the kernel will reconstruct its
contents automatically (without needing the usual mdstop,
replace drive, ckraid, mdrun steps).
´ç½ÅÀÌ ÀÚµ¿ º¹±¸¸¦ ½ÇÇàÇÏÁö ¾Ê¾Ò°í, ±³Ã¼ÇÒ µð½ºÅ©¸¦
¼³Á¤ÇÏÁö ¾Ê¾Ò´Ù¸é, Gadi Oxman <gadio@netvision.net.il> °¡
Á¦¾ÈÇÑ ¾Æ·¡¿Í °°Àº ´Ü°è¸¦ µû¸¦ ¼ö ÀÖ´Ù.
o ÇϳªÀÇ µð½ºÅ©°¡ Á¦°ÅµÇ¾ú´Ù¸é, RAID´Â degraged mode ·Î
¼³Á¤µÇ¾î ÀÛµ¿ÇÒ °ÍÀÌ´Ù. ÀÌ°ÍÀ» full operation mode·Î
À嵿½ÃÅ°±â À§Çؼ´Â ¾Æ·¡¿Í °°Àº ÀýÂ÷°¡ ÇÊ¿äÇÏ´Ù.
o RAID¸¦ ÁߴܽÃÄѶó. (mdstop /dev/md0)
o °íÀå³ µð½ºÅ©¸¦ ±³Ã¼Ç϶ó.
o ³»¿ëº¹±¸¸¦ À§ÇØ ckraid raid.conf ¸¦ ½ÇÇàÇ϶ó.
o RAID¸¦ ´Ù½Ã½ÇÇà½ÃÄѶó. (mdadd, mdrun).
Áß¿äÇÑ Á¡Àº RAID´Â ´Ù½Ã ¸ðµç µå¶óÀ̺꿡¼ µ¹¾Æ°¥ °ÍÀ̶ó´Â
°Í°ú. ÇϳªÀÇ µð½ºÅ©ÀÇ ¹®Á¦°¡ »ý°åÀ» ¶§¸¦ ´ëºñÇÑ °ÍÀ̶ó´Â
°ÍÀÌ´Ù.
ÇöÀçÀÇ ÇϳªÀÇ ±³Ã¼µð½ºÅ©¸¦ ¿©·¯°³ÀÇ RAID¿¡ ¹èºÐÇÏ´Â °ÍÀº
ºÒ°¡´ÉÇÏ´Ù. °¢°¢ÀÇ RAID´Â °¢°¢ÀÇ disk¸¦ ÇÊ¿ä·Î ÇÑ´Ù.
If you are not running automatic reconstruction, and have
not configured a hot-spare disk, the procedure described
by Gadi Oxman <gadio@netvision.net.il> is recommended:
o Currently, once the first disk is removed, the RAID set
will be running in degraded mode. To restore full
operation mode, you need to:
o stop the array (mdstop /dev/md0)
o replace the failed drive
o run ckraid raid.conf to reconstruct its contents
o run the array again (mdadd, mdrun).
At this point, the array will be running with all the
drives, and again protects against a failure of a single
drive.
Currently, it is not possible to assign single hot-spare
disk to several arrays. Each array requires it's own
hot-spare.
10.
Q: Ãʺ¸ °ü¸®ÀÚ°¡ ¹®Á¦°¡ »ý°å´Ù´Â °ÍÀ» ¾Ë ¼ö ÀÖµµ·Ï °°Àº °æ°í¸¦
¼Ò¸®·Î µéÀ» ¼ö Àֱ⸦ ¿øÇÑ´Ù.
A: Ä¿³ÎÀº ``KERN_ALERT'' À̺¥Æ®¿¡ ´ëÇؼ ¿ì¼±ÀûÀ¸·Î syslog¿¡
·Î±×¸¦ ³²±â°í ÀÖ´Ù. syslog¸¦ ¸ð´ÏÅ͸µÇÒ ¸î¸î ¼ÒÇÁÆ®¿þ¾îµéÀÌ
ÀÖ°í, ±×°ÍµéÀÌ ÀÚµ¿ÀûÀ¸·Î PC speaker·Î beep¸¦ ¿ï¸®°Å³ª,
»ß»ß¸¦ È£ÃâÇϰųª. e-mailµîÀ» º¸³¾°ÍÀÌ´Ù.
The kernel is logging the event with a ``KERN_ALERT''
priority in syslog. There are several software packages
that will monitor the syslog files, and beep the PC speaker,
call a pager, send e-mail, etc. automatically.
11.
Q: RAID-5¸¦ ¾î¶»°Ô degraded mode·Î »ç¿ëÇÒ ¼ö Àִ°¡? (µð½ºÅ©
Çϳª¿¡ ¹®Á¦°¡ »ý°å°í, ¾ÆÁ÷ ±³Ã¼ÇÏÁö ¾Ê¾Ò´Ù.)
A: Gadi Oxman <gadio@netvision.net.il> ÀÌ Àû±â¸¦...
ÀϹÝÀûÀ¸·Î, n °³ÀÇ µå¶óÀ̺ê·Î raid-5 ½Ã½ºÅÛÀ» µ¹¸®·Á¸é
¾Æ·¡¿Í °°ÀÌ ÇÑ´Ù.:
mdadd /dev/md0 /dev/disk1 ... /dev/disk(n)
mdrun -p5 /dev/md0
µð½ºÅ©Áß¿¡ Çϳª°¡ ¸Á°¡Áø °æ¿ì¶óµµ ¿©ÀüÈ÷ mdadd¸¦ »ç¿ëÇØ
¼³Á¤ÇØ¾ß ÇÑ´Ù. (?? ¸Á°¡Áø µð½ºÅ© ´ë½Å /dev/nullÀ» »ç¿ëÇؼ
µµÀüÇضó ??? Á¶½ÉÇضó..) (¿ªÀÚ, µ¡. ÀÌ ¹°À½Ç¥´Â ¹»±î... ÀÌ
¹®¼ÀÇ ÀúÀÚ´Â ÀÌ ¹®¼ÀÇ ÀºÎºÐ¿¡¼ ÀÌ ¹æ¹ýÀº ½ÃµµÇØ º»ÀûÀÌ
¾ø´Ù°í Çß´Ù...-.-) RAID´Â (n-1)°³ÀÇ µå¶óÀ̺긦 »ç¿ëÇÑ
degraded mode·Î µ¿ÀÛÇÒ °ÍÀÌ´Ù. ``mdrun''°¡ ½ÇÆÐÇß´Ù¸é, ker
nelÀº ¿¡·¯¸¦ ³¾ °ÍÀÌ´Ù. ( ¸î°³ÀÇ ¹®Á¦°¡ ÀÖ´Â µð½ºÅ©¶óµçÁö,
shutdownÀ» Á¦´ë·Î ¾ÈÇÑ °æ¿ì.) raid-5´Â µð½ºÅ©°¡ Çϳª ±úÁö´Â
°Íº¸´Ù Àü¿øÀÌ ³ª°¬À» ´õ À§ÇèÇϸç, ¾Æ·¡¿Í °°ÀÌ »õ·Î¿î RAID
superblock¸¦ ¸¸µêÀ¸·Î½á º¹±¸¸¦ ½Ãµµ ÇÒ ¼ö ÀÖ´Ù.
mkraid -f --only-superblock raid5.conf
superblockÀÇ º¹±¸´Â ¸ðµç µå¶óÀ̺갡 ''OK'' ·Î Ç¥½ÃµÇ´Â
»óÅÂ(¾Æ¹«Àϵµ ÀϾÁö ¾Ê¾Ò´Ù¸é.)¿¡ ¿µÇâÀ» ¹ÞÁö ¾Ê±â ¶§¹®¿¡
°£´ÜÇÒ °ÍÀÌ´Ù.
Gadi Oxman <gadio@netvision.net.il> writes: Normally, to run
a RAID-5 set of n drives you have to:
mdadd /dev/md0 /dev/disk1 ... /dev/disk(n)
mdrun -p5 /dev/md0
Even if one of the disks has failed, you still have to mdadd
it as you would in a normal setup. (?? try using /dev/null
in place of the failed disk ??? watch out) Then,
The array will be active in degraded mode with (n - 1)
drives. If ``mdrun'' fails, the kernel has noticed an error
(for example, several faulty drives, or an unclean
shutdown). Use ``dmesg'' to display the kernel error
messages from ``mdrun''. If the raid-5 set is corrupted due
to a power loss, rather than a disk crash, one can try to
recover by creating a new RAID superblock:
mkraid -f --only-superblock raid5.conf
A RAID array doesn't provide protection against a power
failure or a kernel crash, and can't guarantee correct
recovery. Rebuilding the superblock will simply cause the
system to ignore the condition by marking all the drives as
``OK'', as if nothing happened.
12.
Q: µð½ºÅ©¿¡ ¹®Á¦°¡ ¹ß»ýÇϸé RAID-5´Â ¾î¶»°Ô µ¿ÀÛÇϳª¿ä?
A: ¾Æ·¡¿Í °°Àº ÀüÇüÀûÀÎ µ¿ÀÛ ´Ü°è°¡ ÀÖ´Ù.
o RAID-5 °¡ ÀÛµ¿ÇÑ´Ù.
o RAID ÀÛµ¿Áß ÇϳªÀÇ µð½ºÅ©¿¡ ¹®Á¦°¡ »ý°å´Ù.
o µå¶óÀ̺êÀÇ firmware¿Í Àú¼öÁØÀÇ Linux µð½ºÅ© ÄÁÆ®·Ñ·¯
µå¶óÀ̹ö´Â ¿À·ù¸¦ °¨ÁöÇÏ°í MD driver¿¡ º¸°íÇÑ´Ù.
o MD driver´Â ³ª¸ÓÁö »ç¿ë°¡´ÉÇÑ µå¶óÀ̺êµé·Î, Ä¿³ÎÀÇ
»óÀ§·¹º§ ºÎºÐ¿¡ ¿¡·¯¿Í °ü°è¾øÀÌ /dev/md0 ¸¦ Á¦°øÇÒ
°ÍÀÌ´Ù. (¼º´ÉÀº ¶³¾îÁø´Ù.)
o °ü¸®ÀÚ´Â ÀϹÝÀûÀ¸·Î umount /dev/md0 °ú mdstop /dev/md0¸¦
ÇÒ ¼ö ÀÖ´Ù.
o °íÀå³ µð½ºÅ©°¡ ±³Ã¼µÇÁö ¾Ê¾Æµµ, °ü¸®ÀÚ´Â mdadd ¿Í
mdrun¸¦ ½ÇÇà½ÃÄѼ. ¿©ÀüÈ÷ degraded mode·Î µ¿ÀÛ½Ãų ¼ö
ÀÖÀ» °ÍÀÌ´Ù.
The typical operating scenario is as follows:
o A RAID-5 array is active.
o One drive fails while the array is active.
o The drive firmware and the low-level Linux
disk/controller drivers detect the failure and report an
error code to the MD driver.
o The MD driver continues to provide an error-free /dev/md0
device to the higher levels of the kernel (with a
performance degradation) by using the remaining
operational drives.
o The sysadmin can umount /dev/md0 and mdstop /dev/md0 as
usual.
o If the failed drive is not replaced, the sysadmin can
still start the array in degraded mode as usual, by
running mdadd and mdrun.
13.
Q:
A:
14.
Q: ¿Ö 13¹ø° Áú¹®Àº ¾ø³ª¿ä?
A: ´ç½ÅÀÌ, RAID¿Í ³ôÀº ´É·Â°ú UPS¿Í °ü·ÃÀÌ ÀÖ´Â »ç¶÷À̶ó¸é,
±×°ÍµéÀ» ¹Ì½ÅÀûÀ¸·Î ¹Ï´Â °Í ¸¶Àúµµ ÁÁÀº »ý°¢ÀÏ °ÍÀÌ´Ù.
±×°ÍÀº Àý´ë ¸Á°¡ÁöÁö ¾ÊÀ» °ÍÀÌ´Ù. ±×·¸Áö ¾ÊÀº°¡?
If you are concerned about RAID, High Availability, and UPS,
then its probably a good idea to be superstitious as well.
It can't hurt, can it?
15.
Q: RAID-5 ½Ã½ºÅÛ¿¡¼ ÇϳªÀÇ °íÀå³ µð½ºÅ©¸¦ ±³Ã¼ÇßÀ» »ÓÀε¥.. RAID
¸¦ º¹±¸ÇÑÈÄ fsck °¡ ¸¹Àº error¸¦ º¸¿©ÁÝ´Ï´Ù. ±×°Ô Á¤»óÀΰ¡¿ä?
A: Á¤»óÀÌ ¾Æ´Ï´Ù. ±×¸®°í fsck¸¦ ¼öÁ¤À» ÇÏÁö ¾Ê´Â °Ë»ç
Àü¿ë¸ðµå¿¡¼ ½ÇÇà½ÃÅ°Áö ¾Ê¾Ò´Ù¸é, µ¥ÀÌÅÍ¿¡ ¹®Á¦°¡ »ý±â´Â
°ÍÀÌ ÃæºÐÈ÷ °¡´ÉÇÏ´Ù. ºÒÇàÇÏ°Ôµµ, µð½ºÅ© ±³Ã¼ÈÄ RAID-5ÀÇ
disk ¼ø¼¸¦ ¿ì¿¬È÷ ¹Ù²Ù¾î ¹ö¸®´Â ÈçÇÑ ½Ç¼ö ÁßÀÇ ÇϳªÀÌ´Ù.
ºñ·Ï RAID superblockÀÌ ¹Ù¶÷Á÷ÇÑ ¹æ¹ýÀ¸·Î ÀúÀåµÇ±ä ÇÏÁö¸¸,
¸ðµç ÅøµéÀÌ ÀÌ Á¤º¸¸¦ µû¸£´Â °ÍÀº ¾Æ´Ï´Ù. Ưº°È÷, ckraid ÀÇ
ÇöÀç ¹öÁ¯Àº -f ¿É¼ÇÀ» »ç¿ëÇؼ ÇöÀç superblock¾ÈÀÇ µ¥ÀÌÅÍ
´ë½Å, Á¤º¸¸¦ Àоî¿Àµµ·Ï ÇÒ ¼ö ÀÖ´Ù. (´ëü·Î
/etc/raid5.confÆÄÀÏÀ» »ç¿ëÇÑ´Ù.) ÁöÁ¤ÇÑ Á¤º¸°¡ ºÎÁ¤È®Çϸé,
±³Ã¼ÇÑ µð½ºÅ©°¡ ºÎÁ¤È®ÇÏ°Ô º¹±¸µÉ °ÍÀÌ°í. ÀÌ·± Á¾·ùÀÇ
½Ç¼öµéÀÌ ¸¹Àº fsck errorµéÀ» ³»´Â Áõ»óÀ» º¸¿©ÁØ´Ù.
±×¸®°í ´ç½ÅÀÌ ½Å±âÇÑ °æ¿ì¿¡(ÀÌ·± ½Ç¼ö·Î ¸ðµç µ¥ÀÌÅ͸¦
¼Õ½Ç´çÇÏ´Â..) ÇØ´çµÈ´Ù¸é, RAIDÀÇ Àç¼³Á¤Àü¿¡ ¸ðµç µ¥ÀÌÅ͸¦
¹é¾÷Çϱ⸦ °·ÂÈ÷ ÃßõÇÑ´Ù.
No. And, unless you ran fsck in "verify only; do not update"
mode, its quite possible that you have corrupted your data.
Unfortunately, a not-uncommon scenario is one of
accidentally changing the disk order in a RAID-5 array,
after replacing a hard drive. Although the RAID superblock
stores the proper order, not all tools use this information.
In particular, the current version of ckraid will use the
information specified with the -f flag (typically, the file
/etc/raid5.conf) instead of the data in the superblock. If
the specified order is incorrect, then the replaced disk
will be reconstructed incorrectly. The symptom of this
kind of mistake seems to be heavy & numerous fsck errors.
And, in case you are wondering, yes, someone lost all of
their data by making this mistake. Making a tape backup of
all data before reconfiguring a RAID array is strongly
recommended.
16.
Q: QuickStart ¿¡¼ mdstop´Â ´ÜÁö µð½ºÅ©µéÀ» µ¿±âÈ(sync)½ÃÅ°´Â °Í
»ÓÀ̶ó°í Çϴµ¥, ±×°Ô Á¤¸» ÇÊ¿äÇÑ °¡¿ä? ÆÄÀϽýºÅÛÀ» unmountÇÏ´Â
°ÍÀ¸·Î ÃæºÐÇÏÁö ¾Ê³ª¿ä?
A:
mdstop /dev/md0 ¸í·ÉÀº.
o shutdownÀÌ Àß µÇ¾ú¼¹´ÂÁö¸¦ ¹ß°ßÇϱâ À§ÇØ,
o RAID¸¦ µ¿±âÈ ½ÃŲ´Ù. ÈÄ¿¡ ÆÄÀϽýºÅÛÀÇ unmountº¸´Ù
Áß¿äÇÏÁö ¾ÊÁö¸¸, ÆÄÀϽýºÅÛÀ» ÅëÇÏ´Â °ÍÀÌ ¾Æ´Ñ,
/dev/md0À» Á÷Á¢ access Çϱ⠶§¹®¿¡, Áß¿äÇÏ´Ù.
The command mdstop /dev/md0 will:
o mark it ''clean''. This allows us to detect unclean
shutdowns, for example due to a power failure or a kernel
crash.
o sync the array. This is less important after unmounting a
filesystem, but is important if the /dev/md0 is accessed
directly rather than through a filesystem (for example,
by e2fsck).
5. ¼³Ä¡¹®Á¦ÀÇ ÇØ°á
1. Q:
2.0.x ´ëÀÇ Ä¿³ÎÀ» À§ÇÑ ÇöÀç ¾Ë·ÁÁø °¡Àå ¾ÈÁ¤µÈ RAID´Â ÆÐÄ¡´Â
¹«¾ùÀΰ¡¿ä?
A:
As of 18 Sept 1997, it is "2.0.30 + pre-9 2.0.31 + Werner
Fink's swapping patch + the alpha RAID patch". As of Novem
ber 1997, it is 2.0.31 + ... !?
2. Q: RAID ÆÐÄ¡°¡ Àü Àß ÀνºÅçµÇÁö ¾Ê³×¿ä. ¹«¾ùÀÌ ¹®Á¦Àϱî¿ä?
A: /usr/include/linux ¸¦ /usr/src/linux/include/linuxÀ¸·Î
½Éº¼¸¯ ¸µÅ©¸¦ °É¾î¶ó. raid5.c µîÀÇ »õÆÄÀÏÀ» Á¦´ë·Î µÈ
À§Ä¡·Î º¹»çÇ϶ó. ¶§¶§·Î ÆÐÄ¡ ¸í·É¾î´Â »õ·Î¿î ÆÄÀÏÀ» ¸¸µéÁö
¸øÇÑ´Ù. ÆÐÄ¡½Ã -f ¿É¼ÇÀ» »ç¿ëÇغ¸¶ó.
Make sure that /usr/include/linux is a symbolic link to
/usr/src/linux/include/linux.
Make sure that the new files raid5.c, etc. have been copied
to their correct locations. Sometimes the patch command
will not create new files. Try the -f flag on patch.
3. Q: raidtools 0.42¸¦ ÄÄÆÄÀÏ Áß include <pthread.h> ¿¡¼, ÄÄÆÄÀÏÀÌ
¸Ü¾ú´Ù. ±×°Ô ³» ½Ã½ºÅÛ¿¡´Â ¾ø´Âµ¥, ¾î¶»°Ô ÀÌ°ÍÀ» °íÃÄ¾ß Çϴ°¡?
A: raidtools-0.42´Â <ftp://ftp.inria.fr/INRIA/Pro
jects/cristal/Xavier.Leroy> ¾òÀ» ¼ö ÀÖ´Â linuxthreads-0.6À»
ÇÊ¿ä·Î ÇÑ´Ù. ¶ÇÇÑ, glibc v2.0µµ »ç¿ëÇÑ´Ù.
raidtools-0.42 requires linuxthreads-0.6 from:
<ftp://ftp.inria.fr/INRIA/Projects/cristal/Xavier.Leroy>
Alternately, use glibc v2.0.
4. Q: ÀÌ·± ¸Þ½ÃÁö°¡ ³ª¿É´Ï´Ù. mdrun -a /dev/md0: Invalid argument
A: ù¹ø° »ç¿ëÇϱâ Àü¿¡ mkraid¸¦ »ç¿ëÇÏ¿© RAID¸¦ ÃʱâÈ
ÇÏ¿©¾ß ÇÑ´Ù.
Use mkraid to initialize the RAID set prior to the first
use. mkraid ensures that the RAID array is initially in a
consistent state by erasing the RAID partitions. In
addition, mkraid will create the RAID superblocks.
5. Q: ÀÌ·± ¸Þ½ÃÁö°¡ ³ª¿É´Ï´Ù. mdrun -a /dev/md0: Invalid argument
¼³Á¤Àº.
o RAID¸¦ kernel ¸ðµâ·Î ¼³Ä¡ÇÏ¿´°í,
o mdcreate, mdadd, µîÀÇ ¼ø¼´ë·Î ÀϹÝÀûÀÎ ÀνºÅçÀ» Çß½À´Ï´Ù.
o cat /proc/mdstat ¸¦ ÇÏ¸é ¾Æ·¡¿Í °°Àº ¸Þ½ÃÁö°¡ ³ª¿É´Ï´Ù.
Personalities :
read_ahead not set
md0 : inactive sda1 sdb1 6313482 blocks
md1 : inactive
md2 : inactive
md3 : inactive
o mdrun -a ·Î ¿À·ù¸¦ Ãâ·ÂÇغ¸¸é.. /dev/md0: Invalid argument ÀÌ·±
¸Þ½ÃÁö°¡ ³ª¿É´Ï´Ù.
A: lsmod (¶Ç´Â cat /proc/modules)·Î raid ¸ðµâÀÌ ·ÎµåµÇ¾ú´ÂÁö
È®ÀÎÇضó. ·ÎµåµÇ¾îÀÖÁö ¾Ê´Ù¸é,modprobe raid1 ¶Ç´Â modprobe
raid5 ·Î È®½ÇÈ÷ ·Îµå½ÃÄѶó. ¶Ç´Â autoloader¸¦ »ç¿ëÇÑ´Ù¸é,
/etc/conf.modules ¿¡ ¾Æ·¡¿Í °°Àº ÁÙÀ» Ãß°¡½ÃÄѶó.
alias md-personality-3 raid1
alias md-personality-4 raid5
Try lsmod (or, alternately, cat /proc/modules) to see if the
raid modules are loaded. If they are not, you can load them
explicitly with the modprobe raid1 or modprobe raid5
command. Alternately, if you are using the autoloader, and
expected kerneld to load them and it didn't this is probably
because your loader is missing the info to load the modules.
Edit /etc/conf.modules and add the following lines:
alias md-personality-3 raid1
alias md-personality-4 raid5
6. Q: mdadd -a ÀÇ ½ÇÇàÁß /dev/md0: No such file or directory ¿Í °°Àº
¸Þ½ÃÁö°¡ ³ª¿Ô½À´Ï´Ù. Á¤¸» ¾îµð¿¡µµ /dev/md0 °¡ ¾ø½À´Ï´Ù. ÀÌ°ÍÀ»
¾î¶»°Ô ÇØ¾ß ÇÒ±î¿ä?
A: raid-tools´Â ·çÆ®°¡ make install ÇßÀ» ¶§, ÀÌ ÀåÄ¡µéÀ»
¸¸µç´Ù. ¶ÇÇÑ, ¾Æ·¡¿Í °°ÀÌ ÇÒ ¼öµµ ÀÖ´Ù.
cd /dev
./MAKEDEV md
The raid-tools package will create these devices when you
run make install as root. Alternately, you can do the
following:
cd /dev
./MAKEDEV md
7. Q: /dev/md0¿¡ RAID¸¦ ¸¸µç ÈÄ mount ½Ãµµ½Ã¿¡ ¾Æ·¡¿Í °°Àº ¿¡·¯°¡
³³´Ï´Ù. ¹«¾ùÀÌ ¹®Á¦ÀԴϱî?
mount: wrong fs type, bad option, bad superblock on /dev/md0, or
too many mounted file systems.
A: ¸¶¿îÆ® ÇϱâÀü¿¡ ÆÄÀϽýºÅÛÀ» ¸¸µé¾î¾ß ÇÑ´Ù. mke2fs¸¦
»ç¿ëÇ϶ó.
You need to create a file system on /dev/md0 before you can
mount it. Use mke2fs.
8. Q: Truxton Fulton ÀÛ¼º: Á¦ 2.0.30 ½Ã½ºÅÛ¿¡¼ mkraid·Î RAID-1À»
À§ÇØ °¢°¢ÀÇ ÆÄƼ¼ÇÀ» Áö¿ì´Â Áß. ÄÜ¼Ö»ó¿¡ "Cannot allocate free
page" ÀÌ·± ¿¡·¯°¡ ³ª°í, system log¿¡ "Unable to handle kernel
paging request at virtual address ..." ÀÌ·± ¿¡·¯°¡ ³³´Ï´Ù.
Truxton Fulton wrote:
On my Linux 2.0.30 system, while doing a mkraid for a RAID-1
device, during the clearing of the two individual parti
tions, I got "Cannot allocate free page" errors appearing on
the console, and "Unable to handle kernel paging request at
virtual address ..." errors in the system log. At this
time, the system became quite unusable, but it appears to
recover after a while. The operation appears to have com
pleted with no other errors, and I am successfully using my
RAID-1 device. The errors are disconcerting though. Any
ideas?
A: ±×°ÍÀº 2.0.30 kernelÀÇ ¾Ë·ÁÁø ¹ö±×ÀÌ´Ù. 2.0.31·Î
¼öÁ¤Çϰųª 2.0.29·Î µ¹¾Æ°¡¶ó.
This was a well-known bug in the 2.0.30 kernels. It is
fixed in the 2.0.31 kernel; alternately, fall back to
2.0.29.
9. Q: mdadd µÈ ÀåÄ¡¸¦ mdrun ÇÏ·Á°í Çϸé, ¾Æ·¡¿Í °°Àº ¸Þ½ÃÁö°¡
³ª¿É´Ï´Ù.
A: mkraid¸¦ ½ÇÇàÇ϶ó.
Make sure that you've run the mkraid part of the install
procedure.
10.
Q: Á¦°¡ /dev/md0À» »ç¿ëÇÏ´Â µ¿¾È, Ä¿³ÎÀº ¾Æ·¡¿Í °°Àº ¿¡·¯µéÀ»
½ñ¾Æ³À´Ï´Ù. md0: device not running, giving up ! , I/O error...
Àü, °¡»ó device¿¡ Á¦ device¸¦ ¼º°øÀûÀ¸·Î Ãß°¡½ÃÄ×¾ú½À´Ï´Ù.
When I access /dev/md0, the kernel spits out a lot of errors like
md0: device not running, giving up ! and I/O error.... I've
successfully added my devices to the virtual device.
A: »ç¿ëÇϱâ À§Çؼ device´Â ½ÇÇàµÇ¾î¾ß ÇÑ´Ù. mdrun -px
/dev/md0¸¦ »ç¿ëÇ϶ó. x´Â RAID levelÀÌ´Ù.
To be usable, the device must be running. Use mdrun -px
/dev/md0 where x is l for linear, 0 for RAID-0 or 1 for
RAID-1, etc.
11.
Q: µÎ°³ÀÇ device¸¦ ¼±Çü ¿¬°áÇؼ md device¸¦ ¸¸µé¾ú½À´Ï´Ù. cat
/proc/mdstat ·Î´Â ÃÑÅ©±â°¡ ³ª¿ÀÁö¸¸, df ¸í·ÉÀ¸·Î´Â ù¹ø° µð½ºÅ©ÀÇ
Å©±â¹Û¿¡ ¾È³ª¿É´Ï´Ù.
I've created a linear md-dev with 2 devices. cat /proc/mdstat
shows the total size of the device, but df only shows the size of
the first physical device.
A: óÀ½ »ç¿ëÇϱâ Àü¿¡ ¹Ýµå½Ã mkfs¸¦ ½ÇÇà¾ß ÇÑ´Ù.
You must mkfs your new md-dev before using it the first
time, so that the filesystem will cover the whole device.
12.
Q: mdcreate·Î /etc/mdtab¸¦ ¼³Á¤ÇÏ°í ,mdadd, mdrun,fsck µîÀ» »ç¿ëÇØ,
µÎ°³ÀÇ /dev/mdX ÆÄƼ¼ÇÀ» ¸¸µé¾ú½À´Ï´Ù. reboot Çϱâ Àü±îÁö ¸ðµç
°ÍÀÌ ±¦Âú¾Æ º¸¿´Áö¸¸, reboot ÇÒ¶§, µÎ ÆÄƼ¼Ç¿¡¼ ¾Æ·¡¿Í °°Àº fsck
°¡ ³µÀ¾´Ï´Ù. fsck.ext2: Attempt to read block from filesystem
resulted in short read while trying too open /dev/md0 ¿Ö ±×·¸°í
¾î¶»°Ô °íÃÄ¾ß Çϳª¿ä?
I've set up /etc/mdtab using mdcreate, I've mdadd'ed, mdrun and
fsck'ed my two /dev/mdX partitions. Everything looks okay before a
reboot. As soon as I reboot, I get an fsck error on both
partitions: fsck.ext2: Attempt to read block from filesystem
resulted in short read while trying too open /dev/md0. Why?! How
do I fix it?!
A: ºÎÆà ÀÛ¾÷½Ã RAID ÆÄƼ¼ÇµéÀº fsckÀÌÀü¿¡ ¹Ýµå½Ã ½ÃÀ۵Ǿî¾ß
ÇÑ´Ù. fsck ´Â /etc/rc.d/rc.S ¶Ç´Â /etc/rc.d/rc.sysinit ¿¡¼
ºÒ·ÁÁú °ÍÀÌ´Ù. ÀÌ ÆÄÀϵéÀÇ fsck -A Àü¿¡ mdadd -ar¸¦
Ãß°¡Çضó.
During the boot process, the RAID partitions must be started before
they can be fsck'ed. This must be done in one of the boot scripts.
For some distributions, fsck is called from /etc/rc.d/rc.S, for
others, it is called from /etc/rc.d/rc.sysinit. Change this file to
mdadd -ar *before* fsck -A is executed. Better yet, it is suggested
that ckraid be run if mdadd returns with an error. How do do this is
discussed in greater detail in question 14 of the section ''Error
Recovery''.
13.
Q: 4GB º¸´Ù Å« ÆÄƼ¼ÇµéÀ» Æ÷ÇÔÇÏ´Â RAID¸¦ ½ÇÇà½ÃÅ°·Á µµÀüÇÒ ¶§
¾Æ·¡¿Í °°Àº ¸Þ½ÃÁö°¡ ³ª¿Ô½À´Ï´Ù. invalid raid superblock magic
A: ÀÌ ¹ö±×´Â ÇöÀç °íÃÄÁ³´Ù.(97³â 9¿ù) ÃÖ±ÙÀÇ raid¹öÁ®À»
»ç¿ëÇضó.
This bug is now fixed. (September 97) Make sure you have
the latest raid code.
14.
Q: 2GBº¸´Ù Å« ÆÄƼ¼ÇÀ¸·Î mke2fs¸¦ ½ÃµµÇϴµ¥ ¾Æ·¡¿Í °°Àº ¿À·ù°¡
³³´Ï´Ù. Warning: could not write 8 blocks in inode table starting
at 2097175
A: ÀÌ°ÍÀº mke2fsÀÇ ¹®Á¦ °°´Ù. Àӽ÷Π¼Ò½º¿¡¼
e2fsprogs-1.10/lib/ext2fs/llseek.c ÆÄÀÏÀÇ Ã¹ #ifdef
HAVE_LLSEEK Àü¿¡ #undef HAVE_LLSEEK ¸¦ Ãß°¡ÇÑÈÄ mke2fs¸¦
ÀçÄÄÆÄÀÏÇؼ »ç¿ëÇ϶ó.
This seems to be a problem with mke2fs (November 97). A
temporary work-around is to get the mke2fs code, and add
#undef HAVE_LLSEEK to e2fsprogs-1.10/lib/ext2fs/llseek.c
just before the first #ifdef HAVE_LLSEEK and recompile
mke2fs.
15.
Q: ckraid °¡ /etc/mdtab ¸¦ ÀÐÁö ¸øÇÕ´Ï´Ù.
A: /etc/mdtab ¾ÈÀÇ RAID-0 / linear RAID ¼³Á¤Àº ¾²ÀÌÁö ¾Ê°í
ÀÖ°í, Á»´õ ÈÄ¿¡¾ß Áö¿ø µÉ°ÍÀÌ´Ù. /etc/raid1.conf µîÀÇ
¼³Á¤ÆÄÀϵéÀ» »ç¿ëÇ϶ó.
The RAID0/linear configuration file format used in
/etc/mdtab is obsolete, although it will be supported for a
while more. The current, up-to-date config files are
currently named /etc/raid1.conf, etc.
16.
Q: (raid1.o) °°Àº ¸ðµâµéÀÌ ÀÚµ¿À¸·Î ·ÎµåµÇÁö ¾Ê½À´Ï´Ù. mdrun Àü¿¡
¼öµ¿À¸·Î modprobe¸¦ ½ÇÇà½ÃÄÑ¾ß Çϴµ¥, ¾î¶»°Ô ÀÌ°ÍÀ» °íÃÄ¾ß ÇÒ±î¿ä?
A: /etc/conf.modules¿¡ ¾Æ·¡¿Í °°Àº ÁÙÀ» Ãß°¡Çضó.
alias md-personality-3 raid1
alias md-personality-4 raid5
To autoload the modules, we can add the following to
/etc/conf.modules:
alias md-personality-3 raid1
alias md-personality-4 raid5
17.
Q: µå¶óÀ̺ê 13°³¸¦ mdadd ÇÑ ÈÄ, mdrun -p5 /dev/md0 ½Ãµµ ÇßÁö¸¸,
¾Æ·¡¿Í °°Àº ¿À·ù°¡ ³ª¿Ô½À´Ï´Ù. /dev/md0: Invalid argument
A: software RAIDÀÇ ±âº»¼³Á¤ 8°³ÀÌ´Ù. linux/md.h ÀÇ #define
MAX_REAL=8 ¸¦ Å©°Ô ¹Ù²ÛÈÄ, Ä¿³ÎÀ» ÀçÄÄÆÄÀÏ Ç϶ó.
The default configuration for software RAID is 8 real
devices. Edit linux/md.h, change #define MAX_REAL=8 to a
larger number, and rebuild the kernel.
18.
Q: ÃÖ½Å½Ä SPARCstation 5 ¿¡¼ md ÀÛ¾÷À» ÇÒ¼ö ¾ø½À´Ï´Ù. µð½ºÅ©
¶óº§¿¡ ¹«½¼ ¹®Á¦°¡ ÀÖ´Â °ÍÀ̶ó°í »ý°¢µË´Ï´Ù¸¸..
I can't make md work with partitions on our latest SPARCstation 5.
I suspect that this has something to do with disk-labels.
A: Sun ÀÇ µð½ºÅ© ¶óº§Àº ÆÄƼ¼ÇÀÇ Ã¹ 1K ¿¡ ÀÖ´Ù.
RAID-1¿¡¼´Â ext2fs ÆÄƼ¼ÇÀÌ ¸ðµç ¶óº§À» ¹«½Ã ÇÒ °ÍÀ̱â
¶§¹®¿¡ ¹®Á¦°¡ ¾øÁö¸¸, ´Ù¸¥ ·¹º§µé¿¡ °üÇؼ´Â ¾ÆÁ÷ ÇØ°áµÇÁö
¾Ê¾Ò´Ù.
Sun disk-labels sit in the first 1K of a partition. For
RAID-1, the Sun disk-label is not an issue since ext2fs will
skip the label on every mirror. For other raid levels (0,
linear and 4/5), this appears to be a problem; it has not
yet (Dec 97) been addressed.
6. Hardware & Software ÀÇ Áö¿ø
1. Q: °¢°¢ ´Ù¸¥ ȸ»çÀÇ µð½ºÅ©¿Í SCSI adapter ·Î RAID¸¦ ±¸¼ºÇÒ ¼ö
Àִ°¡?
I have SCSI adapter brand XYZ (with or without several channels),
and disk brand(s) PQR and LMN, will these work with md to create a
linear/stripped/mirrored personality?
A: ¹°·ÐÀÌ´Ù. ¼ÒÇÁÆ®¿þ¾î RAID´Â ¾î¶² µð½ºÅ©¿Í
µð½ºÅ©ÄÜÆ®·Ñ·¯¿¡¼µµ ÀÛµ¿ÇÑ´Ù, ¿¹¸¦ µé¸é, SCSI¿Í IDE¸¦
¼¯¾î¼ RAID ¸¦ ¸¸µé¼öµµ ÀÖ´Ù. µð½ºÅ© Å©±â°¡ °°À» ÇÊ¿äµµ
¾øÀ¸¸ç, ±× ¿Ü ¾î¶² Á¦¾àµµ ¾ø´Ù.
ÀÌ°ÍÀº µð½ºÅ© ±×´ë·Î°¡ ¾Æ´Ñ, ÆÄƼ¼ÇÀ» »ç¿ëÇϱ⠶§¹®¿¡
°¡´ÉÇÏ´Ù. ´ÜÁö, RAID ·¹º§ 1°ú 5ÀÇ °æ¿ì °°Àº Å©±âÀÇ ÆÄƼ¼ÇÀ»
»ç¿ëÇÒ °ÍÀ» ±ÇÀåÇÒ »ÓÀÌ´Ù. °°Àº Å©±âÀÇ ÆÄƼ¼ÇÀ» »ç¿ëÇÏÁö
¾ÊÀ¸¸é ³²´Â ÆÄƼ¼ÇÀº ¹ö·ÁÁö°Ô µÈ´Ù.
Yes! Software RAID will work with any disk controller (IDE
or SCSI) and any disks. The disks do not have to be
identical, nor do the controllers. For example, a RAID
mirror can be created with one half the mirror being a SCSI
disk, and the other an IDE disk. The disks do not even have
to be the same size. There are no restrictions on the
mixing & matching of disks and controllers.
This is because Software RAID works with disk partitions,
not with the raw disks themselves. The only recommendation
is that for RAID levels 1 and 5, the disk partitions that
are used as part of the same set be the same size. If the
partitions used to make up the RAID 1 or 5 array are not the
same size, then the excess space in the larger partitions is
wasted (not used).
2. Q: ³ª´Â Çϵå¿þ¾î RAID 0,1,0+1À» Áö¿øÇÏ´Â µÎ ä³ÎÂ¥¸® BT-952¸¦
°¡Áö°í ÀÖ´Ù....
I have a twin channel BT-952, and the box states that it supports
hardware RAID 0, 1 and 0+1. I have made a RAID set with two
drives, the card apparently recognizes them when it's doing it's
BIOS startup routine. I've been reading in the driver source code,
but found no reference to the hardware RAID support. Anybody out
there working on that?
A: RAIDPlus ¸¦ Áö¿øÇÏ´Â Mylex/BusLogic FlashPoint º¸µåµéÀº,
ÀüºÎ Çϵå¿þ¾î¸¦ »ç¿ëÇÏ´Â °ÍÀÌ ¾Æ´Ï¶ó, ½ÇÁ¦·Î ¼ÒÇÁÆ®¿þ¾î
RAIDµµ »ç¿ëÇÏ°í, ´ÜÁö Windows 95 and Windows NT¿¡¼¸¸
Áö¿øµÈ´Ù.
The Mylex/BusLogic FlashPoint boards with RAIDPlus are
actually software RAID, not hardware RAID at all. RAIDPlus
is only supported on Windows 95 and Windows NT, not on
Netware or any of the Unix platforms. Aside from booting
and configuration, the RAID support is actually in the OS
drivers.
While in theory Linux support for RAIDPlus is possible, the
implementation of RAID-0/1/4/5 in the Linux kernel is much
more flexible and should have superior performance, so
there's little reason to support RAIDPlus directly.
3. Q: SMP box¿¡¼ RAID¸¦ »ç¿ëÇÏ´Â °ÍÀÌ ¾ÈÀüÇÑ°¡?
I want to run RAID with an SMP box. Is RAID SMP-safe?
A: "³ª´Â ±×·¸°Ô »ý°¢ÇÑ´Ù." °¡ ³»°¡ Áö±Ý ÇÒ¼ö ÀÖ´Â °¡Àå ÁÁÀº
´äÀÌ´Ù. ÃÖ±Ù¿¡ ¸¹Àº À¯ÀúµéÀÌ SMP¿¡¼ÀÇ RAID¿¡ ´ëÇغ¸°íÇÏ°í
ÀÖ´Ù. ÇÏÁö¸¸, ¾Æ·¡¿Í °°Àº ¹®Á¦°¡ ¸ÞÀϸµ ¸®½ºÆ®¸¦ ÅëÇØ
³Ñ¾î¿À±âµµ Çß´Ù.
"I think so" is the best answer available at the time I
write this (April 98). A number of users report that they
have been using RAID with SMP for nearly a year, without
problems. However, as of April 98 (circa kernel 2.1.9x),
the following problems have been noted on the mailing list:
o Adaptec AIC7xxx SCSI drivers are not SMP safe (General
note: Adaptec adapters have a long & lengthly history of
problems & flakiness in general. Although they seem to
be the most easily available, widespread and cheapest
SCSI adapters, they should be avoided. After factoring
for time lost, frustration, and corrupted data, Adaptec's
will prove to be the costliest mistake you'll ever make.
That said, if you have SMP problems with 2.1.88, try the
patch ftp://ftp.bero-
online.ml.org/pub/linux/aic7xxx-5.0.7-linux21.tar.gz I am
not sure if this patch has been pulled into later 2.1.x
kernels. For further info, take a look at the mail
archives for March 98 at
http://www.linuxhq.com/lnxlists/linux-raid/lr_9803_01/ As
usual, due to the rapidly changing nature of the latest
experimental 2.1.x kernels, the problems described in
these mailing lists may or may not have been fixed by the
time your read this. Caveat Emptor. )
o IO-APIC with RAID-0 on SMP has been reported to crash in
2.1.90
7. ÀÌ¹Ì ¼³Ä¡µÈ ½Ã½ºÅÛ ¼öÁ¤Çϱâ.
1. Q: ¼±Çü RAID°¡ È®Àå°¡´ÉÇÑ°¡? µð½ºÅ©¸¦ Ãß°¡Çؼ Á¸ÀçÇÏ´Â ÆÄÀÏ
½Ã½ºÅÛÀÇ Å©±â¸¦ ´Ã¸± ¼ö Àִ°¡?
Are linear MD's expandable? Can a new hard-drive/partition be
added, and the size of the existing file system expanded?
A: Miguel de Icaza <miguel@luthien.nuclecu.unam.mx> ´Â
¾Æ·¡¿Í °°ÀÌ ¸»Çß´Ù.
³ª´Â ÆÄÀÏ ½Ã½ºÅÛ ´ç ÇϳªÀÇ µð½ºÅ©´ë½Å ¿©·¯°³ÀÇ µð½ºÅ©¸¦
»ç¿ëÇÒ °æ¿ì¸¦ ´ëºñÇؼ ext2fsÀÇ ¼Ò½ºÄڵ带 °íÃÆ´Ù. ±×·¡¼,
ÆÄÀÏ ½Ã½ºÅÛÀ» ´Ã¸®°íÀÚ ÇÑ´Ù¸é, À¯Æ¿¸®Æ¼·Î »õµð½ºÅ©¸¦ Àû´çÈ÷
¼³Á¤ÈÄ ´Ù¸¸, ½Ã½ºÅÛ¿¡ ¾Ë¸®±â¸¸ ÇϸéµÈ´Ù. ½Ã½ºÅÛÀÌ ÀÛµ¿Áß¿¡
°ð¹Ù·Î Ãß°¡°¡ °¡´ÉÇÏ°í, ÀçºÎÆÃÇÒ ÇÊ¿ä´Â ¾ø´Ù. ¾Æ·¡ÀÇ
ȨÆäÀÌÁö¿¡¼, 2.1.x¹öÁ¯´ëÀÇ Ä¿³ÎÆÐÄ¡¸¦ ¹Þ¾Æ¶ó.
<http://www.nuclecu.unam.mx/~miguel/ext2-volume>
Miguel de Icaza <miguel@luthien.nuclecu.unam.mx> writes:
I changed the ext2fs code to be aware of multiple-devices
instead of the regular one device per file system assump
tion.
So, when you want to extend a file system, you run a utility program
that makes the appropriate changes on the new device (your extra
partition) and then you just tell the system to extend the fs using
the specified device.
You can extend a file system with new devices at system operation
time, no need to bring the system down (and whenever I get some extra
time, you will be able to remove devices from the ext2 volume set,
again without even having to go to single-user mode or any hack like
that).
You can get the patch for 2.1.x kernel from my web page:
<http://www.nuclecu.unam.mx/~miguel/ext2-volume>
2. Q: RAID-5 ½Ã½ºÅÛ¿¡ µð½ºÅ©¸¦ Ãß°¡ÇÒ ¼ö Àִ°¡?
A: ÇöÀç, ¸ðµç µ¥ÀÌÅ͸¦ Áö¿ìÁö ¾Ê°í´Â ºÒ°¡´ÉÇÏ´Ù. ÄÁ¹öÁ¯ÇÏ´Â
µµ±¸´Â ¾ÆÁ÷ ¾øÀ¸¸ç, RAID-5ÀÇ ½ÇÁ¦Àû ±¸Á¶´Â, diskÀÇ ¼ö¿¡
ÀÇÁ¸Çϱ⠶§¹®ÀÌ´Ù. ¹°·Ð, ¸ðµç µ¥ÀÌÅ͸¦ ¹é¾÷ÇÑÈÄ, ½Ã½ºÅÛÀ»
´Ù½Ã ±¸ÃàÇÏ¸é °¡´ÉÇÏ´Ù.
Currently, (September 1997) no, not without erasing all
data. A conversion utility to allow this does not yet exist.
The problem is that the actual structure and layout of a
RAID-5 array depends on the number of disks in the array.
Of course, one can add drives by backing up the array to
tape, deleting all data, creating a new array, and restoring
from tape.
3. Q: RAID1/RAID0 À¸·Î »ç¿ëÇÏ°í ÀÖ´Â /dev/hdb ¸¦ /dev/hdc·Î À̵¿½ÃÅ°·Á
ÇÕ´Ï´Ù. ¸¸¾à, /etc/mdtab °ú /etc/raid1.confÀÇ ¼³Á¤¸¸ ¹Ù²Û´Ù°í
ÇÑ´Ù¸é, ¾î¶² ÀÏÀÌ ÀϾ±î¿ä?
What would happen to my RAID1/RAID0 sets if I shift one of the
drives from being /dev/hdb to /dev/hdc?
Because of cabling/case size/stupidity issues, I had to make my
RAID sets on the same IDE controller (/dev/hda and /dev/hdb). Now
that I've fixed some stuff, I want to move /dev/hdb to /dev/hdc.
What would happen if I just change the /etc/mdtab and
/etc/raid1.conf files to reflect the new location?
A: linear ¿Í RAID-0¿¡¼´Â Á¤È®È÷ °°Àº ¸í·ÉÀ¸·Î µå¶óÀ̺긦
ÁöÁ¤ÇØ¾ß ÇÑ´Ù. ¿¹¸¦ µé¸é ¿ø·¡ ¼³Á¤ÀÌ, ¾Æ·¡¿Í °°´Ù¸é,
mdadd /dev/md0 /dev/hda /dev/hdb
»õ·Î¿î ¼³Á¤Àº ¹Ýµå½Ã ¾Æ·¡¿Í °°¾Æ¾ß ÇÒ °ÍÀÌ´Ù.
mdadd /dev/md0 /dev/hda /dev/hdc
RAID-1/4/5¿¡¼´Â superblock¿¡ ''RAID number''°¡ ÀúÀåµÇ¾î
Àֱ⠶§¹®¿¡, ¾î¶² µð½ºÅ©¸¦ ÁöÁ¤Çϴ°¡´Â º°·Î Áß¿äÇÏÁö ¾Ê´Ù.
For RAID-0/linear, one must be careful to specify the drives in
exactly the same order. Thus, in the above example, if the original
config is
mdadd /dev/md0 /dev/hda /dev/hdb
Then the new config *must* be
mdadd /dev/md0 /dev/hda /dev/hdc
For RAID-1/4/5, the drive's ''RAID number'' is stored in its RAID
superblock, and therefore the order in which the disks are specified
is not important.
RAID-0/linear does not have a superblock due to it's older design, and
the desire to maintain backwards compatibility with this older design.
4. Q: µð½ºÅ© µÎ°³¸¦ »ç¿ëÇÏ´Â RAID-1 ½Ã½ºÅÛÀ» ¼¼°³ÀÇ µð½ºÅ©¸¦ »ç¿ëÇÏ´Â
RAID-5 ½Ã½ºÅÛÀ¸·Î ¹Ù²Ü¼ö Àִ°¡?
A: ÇÒ¼ö ÀÖ´Ù. BizSystems ÀÇ MichaelÀº ÀÌ°É ½±°Ô ÇÏ´Â ¹æ¹ýÀ»
¸¸µé¾î³Â´Ù. ±×·¯³ª, ½Ç¼ö·Î ÀÎÇØ µ¥ÀÌÅ͸¦ ³¯¸± ¼ö ÀÖÀ¸¹Ç·Î,
ÇÊÈ÷ ¹é¾÷Çسõ±â¸¦ ¹Ù¶õ´Ù.
Yes. Michael at BizSystems has come up with a clever,
sneaky way of doing this. However, like virtually all
manipulations of RAID arrays once they have data on them, it
is dangerous and prone to human error. Make a backup before
you start.
I will make the following assumptions:
---------------------------------------------
disks
original: hda - hdc
raid1 partitions hda3 - hdc3
array name /dev/md0
new hda - hdc - hdd
raid5 partitions hda3 - hdc3 - hdd3
array name: /dev/md1
You must substitute the appropriate disk and partition numbers for
you system configuration. This will hold true for all config file
examples.
--------------------------------------------
DO A BACKUP BEFORE YOU DO ANYTHING
1) recompile kernel to include both raid1 and raid5
2) install new kernel and verify that raid personalities are present
3) disable the redundant partition on the raid 1 array. If this is a
root mounted partition (mine was) you must be more careful.
Reboot the kernel without starting raid devices or boot from rescue
system ( raid tools must be available )
start non-redundant raid1
mdadd -r -p1 /dev/md0 /dev/hda3
4) configure raid5 but with 'funny' config file, note that there is
no hda3 entry and hdc3 is repeated. This is needed since the
raid tools don't want you to do this.
-------------------------------
# raid-5 configuration
raiddev /dev/md1
raid-level 5
nr-raid-disks 3
chunk-size 32
# Parity placement algorithm
parity-algorithm left-symmetric
# Spare disks for hot reconstruction
nr-spare-disks 0
device /dev/hdc3
raid-disk 0
device /dev/hdc3
raid-disk 1
device /dev/hdd3
raid-disk 2
---------------------------------------
mkraid /etc/raid5.conf
5) activate the raid5 array in non-redundant mode
mdadd -r -p5 -c32k /dev/md1 /dev/hdc3 /dev/hdd3
6) make a file system on the array
mke2fs -b {blocksize} /dev/md1
recommended blocksize by some is 4096 rather than the default 1024.
this improves the memory utilization for the kernel raid routines and
matches the blocksize to the page size. I compromised and used 2048
since I have a relatively high number of small files on my system.
7) mount the two raid devices somewhere
mount -t ext2 /dev/md0 mnt0
mount -t ext2 /dev/md1 mnt1
8) move the data
cp -a mnt0 mnt1
9) verify that the data sets are identical
10) stop both arrays
11) correct the information for the raid5.conf file
change /dev/md1 to /dev/md0
change the first disk to read /dev/hda3
12) upgrade the new array to full redundant status
(THIS DESTROYS REMAINING raid1 INFORMATION)
ckraid --fix /etc/raid5.conf
8. ¼º´É°ú µµ±¸, ÀϹÝÀûÀÎ °Íµé¿¡ °üÇÑ ¸ÛûÇÑ Áú¹®µé.
1. Q:
I've created a RAID-0 device on /dev/sda2 and /dev/sda3. The device
is a lot slower than a single partition. Isn't md a pile of junk?
A:
To have a RAID-0 device running a full speed, you must have
partitions from different disks. Besides, putting the two
halves of the mirror on the same disk fails to give you any
protection whatsoever against disk failure.
2. Q:
What's the use of having RAID-linear when RAID-0 will do the same
thing, but provide higher performance?
A:
It's not obvious that RAID-0 will always provide better per
formance; in fact, in some cases, it could make things
worse. The ext2fs file system scatters files all over a
partition, and it attempts to keep all of the blocks of a
file contiguous, basically in an attempt to prevent fragmen
tation. Thus, ext2fs behaves "as if" there were a (vari
able-sized) stripe per file. If there are several disks
concatenated into a single RAID-linear, this will result
files being statistically distributed on each of the disks.
Thus, at least for ext2fs, RAID-linear will behave a lot
like RAID-0 with large stripe sizes. Conversely, RAID-0
with small stripe sizes can cause excessive disk activity
leading to severely degraded performance if several large
files are accessed simultaneously.
In many cases, RAID-0 can be an obvious win. For example,
imagine a large database file. Since ext2fs attempts to
cluster together all of the blocks of a file, chances are
good that it will end up on only one drive if RAID-linear is
used, but will get chopped into lots of stripes if RAID-0 is
used. Now imagine a number of (kernel) threads all trying
to random access to this database. Under RAID-linear, all
accesses would go to one disk, which would not be as
efficient as the parallel accesses that RAID-0 entails.
3. Q:
How does RAID-0 handle a situation where the different stripe
partitions are different sizes? Are the stripes uniformly
distributed?
A: To understand this, lets look at an example with three
partitions; one that is 50MB, one 90MB and one 125MB.
Lets call D0 the 50MB disk, D1 the 90MB disk and D2 the 125MB disk.
When you start the device, the driver calculates 'strip zones'. In
this case, it finds 3 zones, defined like this:
Z0 : (D0/D1/D2) 3 x 50 = 150MB total in this zone
Z1 : (D1/D2) 2 x 40 = 80MB total in this zone
Z2 : (D2) 125-50-40 = 35MB total in this zone.
You can see that the total size of the zones is the size of the
virtual device, but, depending on the zone, the striping is different.
Z2 is rather inefficient, since there's only one disk.
Since ext2fs and most other Unix file systems distribute files all
over the disk, you have a 35/265 = 13% chance that a fill will end up
on Z2, and not get any of the benefits of striping.
(DOS tries to fill a disk from beginning to end, and thus, the oldest
files would end up on Z0. However, this strategy leads to severe
filesystem fragmentation, which is why no one besides DOS does it this
way.)
4. Q: I have some Brand X hard disks and a Brand Y controller. and am
considering using md. Does it significantly increase the
throughput? Is the performance really noticeable?
A: The answer depends on the configuration that you use.
Linux MD RAID-0 and RAID-linear performance:
If the system is heavily loaded with lots of I/O,
statistically, some of it will go to one disk, and
some to the others. Thus, performance will improve
over a single large disk. The actual improvement
depends a lot on the actual data, stripe sizes, and
other factors. In a system with low I/O usage, the
performance is equal to that of a single disk.
Linux MD RAID-1 (mirroring) read performance:
MD implements read balancing. That is, the RAID-1
code will alternate between each of the (two or more)
disks in the mirror, making alternate reads to each.
In a low-I/O situation, this won't change performance
at all: you will have to wait for one disk to complete
the read. But, with two disks in a high-I/O
environment, this could as much as double the read
performance, since reads can be issued to each of the
disks in parallel. For N disks in the mirror, this
could improve performance N-fold.
Linux MD RAID-1 (mirroring) write performance:
Must wait for the write to occur to all of the disks
in the mirror. This is because a copy of the data
must be written to each of the disks in the mirror.
Thus, performance will be roughly equal to the write
performance to a single disk.
Linux MD RAID-4/5 read performance:
Statistically, a given block can be on any one of a
number of disk drives, and thus RAID-4/5 read
performance is a lot like that for RAID-0. It will
depend on the data, the stripe size, and the
application. It will not be as good as the read
performance of a mirrored array.
Linux MD RAID-4/5 write performance:
This will in general be considerably slower than that
for a single disk. This is because the parity must be
written out to one drive as well as the data to
another. However, in order to compute the new parity,
the old parity and the old data must be read first.
The old data, new data and old parity must all be
XOR'ed together to determine the new parity: this
requires considerable CPU cycles in addition to the
numerous disk accesses.
5. Q: What RAID configuration should I use for optimal performance?
A: Is the goal to maximize throughput, or to minimize
latency? There is no easy answer, as there are many factors
that affect performance:
o operating system - will one process/thread, or many be
performing disk access?
o application - is it accessing data in a sequential
fashion, or random access?
o file system - clusters files or spreads them out
(the ext2fs clusters together the blocks of a file, and
spreads out files)
o disk driver - number of blocks to read ahead (this
is a tunable parameter)
o CEC hardware - one drive controller, or many?
o hd controller - able to queue multiple requests or
not? Does it provide a cache?
o hard drive - buffer cache memory size -- is it big
enough to handle the write sizes and rate you want?
o physical platters - blocks per cylinder -- accessing
blocks on different cylinders will lead to seeks.
6. Q: What is the optimal RAID-5 configuration for performance?
A: Since RAID-5 experiences an I/O load that is equally dis
tributed across several drives, the best performance will be
obtained when the RAID set is balanced by using identical
drives, identical controllers, and the same (low) number of
drives on each controller.
Note, however, that using identical components will raise
the probability of multiple simultaneous failures, for exam
ple due to a sudden jolt or drop, overheating, or a power
surge during an electrical storm. Mixing brands and models
helps reduce this risk.
7. Q: What is the optimal block size for a RAID-4/5 array?
A: When using the current (November 1997) RAID-4/5 implemen
tation, it is strongly recommended that the file system be
created with mke2fs -b 4096 instead of the default 1024 byte
filesystem block size.
This is because the current RAID-5 implementation allocates
one 4K memory page per disk block; if a disk block were just
1K in size, then 75% of the memory which RAID-5 is
allocating for pending I/O would not be used. If the disk
block size matches the memory page size, then the driver can
(potentially) use all of the page. Thus, for a filesystem
with a 4096 block size as opposed to a 1024 byte block size,
the RAID driver will potentially queue 4 times as much
pending I/O to the low level drivers without allocating
additional memory.
Note: the above remarks do NOT apply to Software
RAID-0/1/linear driver.
Note: the statements about 4K memory page size apply to the
Intel x86 architecture. The page size on Alpha, Sparc, and
other CPUS are different; I believe they're 8K on
Alpha/Sparc (????). Adjust the above figures accordingly.
Note: if your file system has a lot of small files (files
less than 10KBytes in size), a considerable fraction of the
disk space might be wasted. This is because the file system
allocates disk space in multiples of the block size.
Allocating large blocks for small files clearly results in a
waste of disk space: thus, you may want to stick to small
block sizes, get a larger effective storage capacity, and
not worry about the "wasted" memory due to the block-
size/page-size mismatch.
Note: most ''typical'' systems do not have that many small
files. That is, although there might be thousands of small
files, this would lead to only some 10 to 100MB wasted
space, which is probably an acceptable tradeoff for
performance on a multi-gigabyte disk.
However, for news servers, there might be tens or hundreds
of thousands of small files. In such cases, the smaller
block size, and thus the improved storage capacity, may be
more important than the more efficient I/O scheduling.
Note: there exists an experimental file system for Linux
which packs small files and file chunks onto a single block.
It apparently has some very positive performance
implications when the average file size is much smaller than
the block size.
Note: Future versions may implement schemes that obsolete
the above discussion. However, this is difficult to
implement, since dynamic run-time allocation can lead to
dead-locks; the current implementation performs a static
pre-allocation.
8. Q: How does the chunk size (stripe size) influence the speed of my
RAID-0, RAID-4 or RAID-5 device?
A: The chunk size is the amount of data contiguous on the
virtual device that is also contiguous on the physical
device. In this HOWTO, "chunk" and "stripe" refer to the
same thing: what is commonly called the "stripe" in other
RAID documentation is called the "chunk" in the MD man
pages. Stripes or chunks apply only to RAID 0, 4 and 5,
since stripes are not used in mirroring (RAID-1) and simple
concatenation (RAID-linear). The stripe size affects both
read and write latency (delay), throughput (bandwidth), and
contention between independent operations (ability to simul
taneously service overlapping I/O requests).
Assuming the use of the ext2fs file system, and the current
kernel policies about read-ahead, large stripe sizes are
almost always better than small stripe sizes, and stripe
sizes from about a fourth to a full disk cylinder in size
may be best. To understand this claim, let us consider the
effects of large stripes on small files, and small stripes
on large files. The stripe size does not affect the read
performance of small files: For an array of N drives, the
file has a 1/N probability of being entirely within one
stripe on any one of the drives. Thus, both the read
latency and bandwidth will be comparable to that of a single
drive. Assuming that the small files are statistically well
distributed around the filesystem, (and, with the ext2fs
file system, they should be), roughly N times more
overlapping, concurrent reads should be possible without
significant collision between them. Conversely, if very
small stripes are used, and a large file is read
sequentially, then a read will issued to all of the disks in
the array. For a the read of a single large file, the
latency will almost double, as the probability of a block
being 3/4'ths of a revolution or farther away will increase.
Note, however, the trade-off: the bandwidth could improve
almost N-fold for reading a single, large file, as N drives
can be reading simultaneously (that is, if read-ahead is
used so that all of the disks are kept active). But there
is another, counter-acting trade-off: if all of the drives
are already busy reading one file, then attempting to read a
second or third file at the same time will cause significant
contention, ruining performance as the disk ladder
algorithms lead to seeks all over the platter. Thus, large
stripes will almost always lead to the best performance. The
sole exception is the case where one is streaming a single,
large file at a time, and one requires the top possible
bandwidth, and one is also using a good read-ahead
algorithm, in which case small stripes are desired.
Note that this HOWTO previously recommended small stripe
sizes for news spools or other systems with lots of small
files. This was bad advice, and here's why: news spools
contain not only many small files, but also large summary
files, as well as large directories. If the summary file is
larger than the stripe size, reading it will cause many
disks to be accessed, slowing things down as each disk
performs a seek. Similarly, the current ext2fs file system
searches directories in a linear, sequential fashion. Thus,
to find a given file or inode, on average half of the
directory will be read. If this directory is spread across
several stripes (several disks), the directory read (e.g.
due to the ls command) could get very slow. Thanks to Steven
A. Reisman <sar@pressenter.com> for this correction. Steve
also adds:
I found that using a 256k stripe gives much better perfor
mance. I suspect that the optimum size would be the size of
a disk cylinder (or maybe the size of the disk drive's sec
tor cache). However, disks nowadays have recording zones
with different sector counts (and sector caches vary among
different disk models). There's no way to guarantee stripes
won't cross a cylinder boundary.
The tools accept the stripe size specified in KBytes. You'll want to
specify a multiple of if the page size for your CPU (4KB on the x86).
9. Q: What is the correct stride factor to use when creating the
ext2fs file system on the RAID partition? By stride, I mean the -R
flag on the mke2fs command:
mke2fs -b 4096 -R stride=nnn ...
What should the value of nnn be?
A: The -R stride flag is used to tell the file system about
the size of the RAID stripes. Since only RAID-0,4 and 5 use
stripes, and RAID-1 (mirroring) and RAID-linear do not, this
flag is applicable only for RAID-0,4,5.
Knowledge of the size of a stripe allows mke2fs to allocate
the block and inode bitmaps so that they don't all end up on
the same physical drive. An unknown contributor wrote:
I noticed last spring that one drive in a pair always had a
larger I/O count, and tracked it down to the these meta-data
blocks. Ted added the -R stride= option in response to my
explanation and request for a workaround.
For a 4KB block file system, with stripe size 256KB, one would use -R
stride=64.
If you don't trust the -R flag, you can get a similar effect in a
different way. Steven A. Reisman <sar@pressenter.com> writes:
Another consideration is the filesystem used on the RAID-0
device. The ext2 filesystem allocates 8192 blocks per
group. Each group has its own set of inodes. If there are
2, 4 or 8 drives, these inodes cluster on the first disk.
I've distributed the inodes across all drives by telling
mke2fs to allocate only 7932 blocks per group.
Some mke2fs pages do not describe the [-g blocks-per-group] flag used
in this operation.
10.
Q: Where can I put the md commands in the startup scripts, so that
everything will start automatically at boot time?
A: Rod Wilkens <rwilkens@border.net> writes:
What I did is put ``mdadd -ar'' in the
``/etc/rc.d/rc.sysinit'' right after the kernel loads the
modules, and before the ``fsck'' disk check. This way, you
can put the ``/dev/md?'' device in the ``/etc/fstab''. Then
I put the ``mdstop -a'' right after the ``umount -a''
unmounting the disks, in the ``/etc/rc.d/init.d/halt'' file.
For raid-5, you will want to look at the return code for mdadd, and if
it failed, do a
ckraid --fix /etc/raid5.conf
to repair any damage.
11.
Q: I was wondering if it's possible to setup striping with more
than 2 devices in md0? This is for a news server, and I have 9
drives... Needless to say I need much more than two. Is this
possible?
A: Yes. (describe how to do this)
12.
Q: When is Software RAID superior to Hardware RAID?
A: Normally, Hardware RAID is considered superior to Soft
ware RAID, because hardware controllers often have a large
cache, and can do a better job of scheduling operations in
parallel. However, integrated Software RAID can (and does)
gain certain advantages from being close to the operating
system.
For example, ... ummm. Opaque description of caching of
reconstructed blocks in buffer cache elided ...
On a dual PPro SMP system, it has been reported that
Software-RAID performance exceeds the performance of a well-
known hardware-RAID board vendor by a factor of 2 to 5.
Software RAID is also a very interesting option for high-
availability redundant server systems. In such a
configuration, two CPU's are attached to one set or SCSI
disks. If one server crashes or fails to respond, then the
other server can mdadd, mdrun and mount the software RAID
array, and take over operations. This sort of dual-ended
operation is not always possible with many hardware RAID
controllers, because of the state configuration that the
hardware controllers maintain.
13.
Q: If I upgrade my version of raidtools, will it have trouble
manipulating older raid arrays? In short, should I recreate my
RAID arrays when upgrading the raid utilities?
A: No, not unless the major version number changes. An MD
version x.y.z consists of three sub-versions:
x: Major version.
y: Minor version.
z: Patchlevel version.
Version x1.y1.z1 of the RAID driver supports a RAID array
with version x2.y2.z2 in case (x1 == x2) and (y1 >= y2).
Different patchlevel (z) versions for the same (x.y) version
are designed to be mostly compatible.
The minor version number is increased whenever the RAID
array layout is changed in a way which is incompatible with
older versions of the driver. New versions of the driver
will maintain compatibility with older RAID arrays.
The major version number will be increased if it will no
longer make sense to support old RAID arrays in the new
kernel code.
For RAID-1, it's not likely that the disk layout nor the
superblock structure will change anytime soon. Most all Any
optimization and new features (reconstruction, multithreaded
tools, hot-plug, etc.) doesn't affect the physical layout.
14.
Q: The command mdstop /dev/md0 says that the device is busy.
A: There's a process that has a file open on /dev/md0, or
/dev/md0 is still mounted. Terminate the process or umount
/dev/md0.
15.
Q: Are there performance tools?
A: There is also a new utility called iotrace in the
linux/iotrace directory. It reads /proc/io-trace and analy
ses/plots it's output. If you feel your system's block IO
performance is too low, just look at the iotrace output.
16.
Q: I was reading the RAID source, and saw the value SPEED_LIMIT
defined as 1024K/sec. What does this mean? Does this limit
performance?
A: SPEED_LIMIT is used to limit RAID reconstruction speed
during automatic reconstruction. Basically, automatic
reconstruction allows you to e2fsck and mount immediately
after an unclean shutdown, without first running ckraid.
Automatic reconstruction is also used after a failed hard
drive has been replaced.
In order to avoid overwhelming the system while
reconstruction is occurring, the reconstruction thread
monitors the reconstruction speed and slows it down if its
too fast. The 1M/sec limit was arbitrarily chosen as a
reasonable rate which allows the reconstruction to finish
reasonably rapidly, while creating only a light load on the
system so that other processes are not interfered with.
17.
Q: What about ''spindle synchronization'' or ''disk
synchronization''?
A: Spindle synchronization is used to keep multiple hard
drives spinning at exactly the same speed, so that their
disk platters are always perfectly aligned. This is used by
some hardware controllers to better organize disk writes.
However, for software RAID, this information is not used,
and spindle synchronization might even hurt performance.
18.
Q: How can I set up swap spaces using raid 0? Wouldn't striped
swap ares over 4+ drives be really fast?
A: Leonard N. Zubkoff replies: It is really fast, but you
don't need to use MD to get striped swap. The kernel auto
matically stripes across equal priority swap spaces. For
example, the following entries from /etc/fstab stripe swap
space across five drives in three groups:
/dev/sdg1 swap swap pri=3
/dev/sdk1 swap swap pri=3
/dev/sdd1 swap swap pri=3
/dev/sdh1 swap swap pri=3
/dev/sdl1 swap swap pri=3
/dev/sdg2 swap swap pri=2
/dev/sdk2 swap swap pri=2
/dev/sdd2 swap swap pri=2
/dev/sdh2 swap swap pri=2
/dev/sdl2 swap swap pri=2
/dev/sdg3 swap swap pri=1
/dev/sdk3 swap swap pri=1
/dev/sdd3 swap swap pri=1
/dev/sdh3 swap swap pri=1
/dev/sdl3 swap swap pri=1
19.
Q: I want to maximize performance. Should I use multiple
controllers?
A: In many cases, the answer is yes. Using several con
trollers to perform disk access in parallel will improve
performance. However, the actual improvement depends on
your actual configuration. For example, it has been
reported (Vaughan Pratt, January 98) that a single 4.3GB
Cheetah attached to an Adaptec 2940UW can achieve a rate of
14MB/sec (without using RAID). Installing two disks on one
controller, and using a RAID-0 configuration results in a
measured performance of 27 MB/sec.
Note that the 2940UW controller is an "Ultra-Wide" SCSI
controller, capable of a theoretical burst rate of 40MB/sec,
and so the above measurements are not surprising. However,
a slower controller attached to two fast disks would be the
bottleneck. Note also, that most out-board SCSI enclosures
(e.g. the kind with hot-pluggable trays) cannot be run at
the 40MB/sec rate, due to cabling and electrical noise
problems.
If you are designing a multiple controller system, remember
that most disks and controllers typically run at 70-85% of
their rated max speeds.
Note also that using one controller per disk can reduce the
likelihood of system outage due to a controller or cable
failure (In theory -- only if the device driver for the
controller can gracefully handle a broken controller. Not
all SCSI device drivers seem to be able to handle such a
situation without panicking or otherwise locking up).
9. °í °¡¿ë¼º(High-Availability) RAID
1. Q: RAID´Â µ¥ÀÌÅÍ ¼Õ½ÇÀ» ¸·¾ÆÁÙ ¼ö ÀÖ´Ù, ÇÏÁö¸¸, ½Ã½ºÅÛÀ» ¼Õ»ó¾øÀÌ
°¡´ÉÇÑ ¿À·¡ ÄѳõÀ» ¼ö Àִ°¡?
RAID can help protect me against data loss. But how can I also
ensure that the system is up as long as possible, and not prone to
breakdown? Ideally, I want a system that is up 24 hours a day, 7
days a week, 365 days a year.
A: °í °¡¿ë¼º(High-Availability)Àº Á» ´õ ¾î·Æ°í ºñ½Ñ °ÍÀÌ´Ù.
¾Æ·¡ÀÇ hint¿Í tip, »ý°¢, ¼Ò¹®ÀÌ ±× ¹®Á¦¿¡ ´ëÇؼ µµ¿ÍÁÙ
°ÍÀÌ´Ù.
o °°Àº IDE ¸®º» ÄÉÀÌºí¿¡ ¿¬°áµÈ µð½ºÅ©Áß Çϳª¿¡ ¿À·ù°¡
³ª¸é, µð½ºÅ© µÎ°³°¡ ¸ðµÎ ¸Á°¡Áø °ÍÀ¸·Î ÀÎ½ÄµÉ °ÍÀÌ´Ù.
ÇϳªÀÇ IDE ÄÉÀÌºí¿¡´Â ÇϳªÀÇ µð½ºÅ©¸¸À» »ç¿ëÇضó.
o SCSI chain ¿ª½Ã ÇϳªÀÇ ¿À·ùµð½ºÅ©°¡ ¸ðµç µð½ºÅ©¿¡ Á¢±Ù
¸øÇÏ°Ô ÇÒ°ÍÀÌ´Ù. °°Àº SCSI chain¿¡ °°Àº RAID ½Ã½ºÅÛÀÇ
µð½ºÅ©µéÀ» µÎÁö ¸»¾Æ¶ó.
o µð½ºÅ© ÄÜÆ®·Ñ·¯µµ ¿ª½Ã ¿©·¯°³¸¦ »ç¿ëÇ϶ó.
o ¸ðµç µð½ºÅ©¸¦ °°Àº ȸ»ç, °°Àº ¸ðµ¨·Î ¾²Áö ¸»¾Æ¶ó.
µð½ºÅ©µéÀÌ ¹°¸®ÀûÀÎ Ãæ°ÝÀ» ¹ÞÀ» °æ¿ì Á» ´õ ¾ÈÀüÇÒ °ÍÀÌ´Ù.
o CPU³ª ÄÜÆ®·Ñ·¯ÀÇ ½ÇÆÐÇÒ °æ¿ì¿¡ ´ëºñÇؼ SCSI¸¦ µÎ°³ÀÇ
ÄÄÇ»ÅÍ¿Í ¿¬°áµÇ´Â "twin-tailed" »óÅ·Π¼³Á¤ÇÒ ¼ö ÀÖÀ»
°ÍÀÌ´Ù. (¾Æ·¡ ¿ø¹®À» Âü°í ÇϽñæ.. -.-; ÂÁ.)
o Ç×»ó UPS¸¦ »ç¿ëÇÏ°í shutdownÀ» Ç϶ó.
o SCSI ÄÉÀ̺íÀº ¸Å¿ì ±î´Ù·Ó°í, ¹®Á¦°¡ µÇ±â ½¬¿î °ÍÀ¸·Î
¾Ë·ÁÀú ÀÖ´Ù. »ì ¼ö ÀÖ´Â °¡Àå ÁÁÀº ÁúÀÇ ÄÉÀ̺íÀ»
»ç¿ëÇضó.
o SSI (Serial Storage Architecture) ¸¦ º¸°í ´Ù¼Ò ºñ½Î´õ¶óµµ
¾ÈÀüÇÏ´Ù°í ¾Ë·ÁÁø Á¦Ç°À» »ç¿ëÇضó.
o Áñ°Ü¶ó, ¸Á°¡Áö´Â °ÍÀº ´ç½ÅÀÌ »ý°¢ÇÏ´Â °Íº¸´Ù ³ªÁß ÀÏÀÏ
°ÍÀÌ´Ù.
High-Availability is difficult and expensive. The harder you try to
make a system be fault tolerant, the harder and more expensive it
gets. The following hints, tips, ideas and unsubstantiated rumors
may help you with this quest.
o IDE disks can fail in such a way that the failed disk on an IDE
ribbon can also prevent the good disk on the same ribbon from
responding, thus making it look as if two disks have failed.
Since RAID does not protect against two-disk failures, one should
either put only one disk on an IDE cable, or if there are two
disks, they should belong to different RAID sets.
o SCSI disks can fail in such a way that the failed disk on a SCSI
chain can prevent any device on the chain from being accessed. The
failure mode involves a short of the common (shared) device ready
pin; since this pin is shared, no arbitration can occur until the
short is removed. Thus, no two disks on the same SCSI chain should
belong to the same RAID array.
o Similar remarks apply to the disk controllers. Don't load up the
channels on one controller; use multiple controllers.
o Don't use the same brand or model number for all of the disks. It
is not uncommon for severe electrical storms to take out two or
more disks. (Yes, we all use surge suppressors, but these are not
perfect either). Heat & poor ventilation of the disk enclosure
are other disk killers. Cheap disks often run hot. Using
different brands of disk & controller decreases the likelihood that
whatever took out one disk (heat, physical shock, vibration,
electrical surge) will also damage the others on the same date.
o To guard against controller or CPU failure, it should be possible
to build a SCSI disk enclosure that is "twin-tailed": i.e. is
connected to two computers. One computer will mount the file-
systems read-write, while the second computer will mount them read-
only, and act as a hot spare. When the hot-spare is able to
determine that the master has failed (e.g. through a watchdog), it
will cut the power to the master (to make sure that it's really
off), and then fsck & remount read-write. If anyone gets this
working, let me know.
o Always use an UPS, and perform clean shutdowns. Although an
unclean shutdown may not damage the disks, running ckraid on even
small-ish arrays is painfully slow. You want to avoid running
ckraid as much as possible. Or you can hack on the kernel and get
the hot-reconstruction code debugged ...
o SCSI cables are well-known to be very temperamental creatures, and
prone to cause all sorts of problems. Use the highest quality
cabling that you can find for sale. Use e.g. bubble-wrap to make
sure that ribbon cables to not get too close to one another and
cross-talk. Rigorously observe cable-length restrictions.
o Take a look at SSI (Serial Storage Architecture). Although it is
rather expensive, it is rumored to be less prone to the failure
modes that SCSI exhibits.
o Enjoy yourself, its later than you think.
10. ´äº¯À» ±â´Ù¸®´Â Áú¹®µé.
1. Q: If, for cost reasons, I try to mirror a slow disk with a fast
disk, is the S/W smart enough to balance the reads accordingly or
will it all slow down to the speed of the slowest?
2. Q: For testing the raw disk thru put... is there a character
device for raw read/raw writes instead of /dev/sdaxx that we can
use to measure performance on the raid drives?? is there a GUI
based tool to use to watch the disk thru-put??
11. Ãß°¡µÇ¾îÁö±â ¹Ù¶ó´Â ±â´Éµé..
Bradley Ward Allen <ulmo@Q.Net> wrote:
Ideas include:
o Boot-up parameters to tell the kernel which devices are
to be MD devices (no more ``mdadd'')
o Making MD transparent to ``mount''/``umount'' such that
there is no ``mdrun'' and ``mdstop''
o Integrating ``ckraid'' entirely into the kernel, and
letting it run as needed
(So far, all I've done is suggest getting rid of the
tools and putting them into the kernel; that's how I feel
about it, this is a filesystem, not a toy.)
o Deal with arrays that can easily survive N disks going
out simultaneously or at separate moments, where N is a
whole number > 0 settable by the administrator
o Handle kernel freezes, power outages, and other abrupt
shutdowns better
o Don't disable a whole disk if only parts of it have
failed, e.g., if the sector errors are confined to less
than 50% of access over the attempts of 20 dissimilar
requests, then it continues just ignoring those sectors
of that particular disk.
o Bad sectors:
o A mechanism for saving which sectors are bad, someplace
onto the disk.
o If there is a generalized mechanism for marking degraded
bad blocks that upper filesystem levels can recognize,
use that. Program it if not.
o Perhaps alternatively a mechanism for telling the upper
layer that the size of the disk got smaller, even
arranging for the upper layer to move out stuff from the
areas being eliminated. This would help with a degraded
blocks as well.
o Failing the above ideas, keeping a small (admin settable)
amount of space aside for bad blocks (distributed evenly
across disk?), and using them (nearby if possible)
instead of the bad blocks when it does happen. Of
course, this is inefficient. Furthermore, the kernel
ought to log every time the RAID array starts each bad
sector and what is being done about it with a ``crit''
level warning, just to get the administrator to realize
that his disk has a piece of dust burrowing into it (or a
head with platter sickness).
o Software-switchable disks:
``disable this disk''
would block until kernel has completed making sure
there is no data on the disk being shut down that is
needed (e.g., to complete an XOR/ECC/other error
correction), then release the disk from use (so it
could be removed, etc.);
``enable this disk''
would mkraid a new disk if appropriate and then start
using it for ECC/whatever operations, enlarging the
RAID5 array as it goes;
``resize array''
would respecify the total number of disks and the
number of redundant disks, and the result would often
be to resize the size of the array; where no data loss
would result, doing this as needed would be nice, but
I have a hard time figuring out how it would do that;
in any case, a mode where it would block (for possibly
hours (kernel ought to log something every ten seconds
if so)) would be necessary;
``enable this disk while saving data''
which would save the data on a disk as-is and move it
to the RAID5 system as needed, so that a horrific save
and restore would not have to happen every time
someone brings up a RAID5 system (instead, it may be
simpler to only save one partition instead of two, it
might fit onto the first as a gzip'd file even);
finally,
``re-enable disk''
would be an operator's hint to the OS to try out a
previously failed disk (it would simply call disable
then enable, I suppose).
Other ideas off the net:
o finalrd analog to initrd, to simplify root raid.
o a read-only raid mode, to simplify the above
o Mark the RAID set as clean whenever there are no "half
writes" done. -- That is, whenever there are no write
transactions that were committed on one disk but still
unfinished on another disk.
Add a "write inactivity" timeout (to avoid frequent seeks
to the RAID superblock when the RAID set is relatively
busy).
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