OCFS2 - Frequently Asked Questions
==================================
General
-------
Q01 How do I get started?
A01 a) Download and install the module and tools rpms.
b) Create cluster.conf and propagate to all nodes.
c) Configure and start the O2CB cluster service.
d) Format the volume.
e) Mount the volume.
Q02 How do I know the version number running?
A02 # cat /proc/fs/ocfs2/version
OCFS2 1.2.1 Fri Apr 21 13:51:24 PDT 2006 (build bd2f25ba0af9677db3572e3ccd92f739)
Q03 How do I configure my system to auto-reboot after a panic?
A03 To auto-reboot system 60 secs after a panic, do:
# echo 60 > /proc/sys/kernel/panic
To enable the above on every reboot, add the following to
/etc/sysctl.conf:
kernel.panic = 60
==============================================================================
Download and Install
--------------------
Q01 Where do I get the packages from?
A01 For Novell's SLES9, upgrade to SP3 to get the required modules
installed. Also, install ocfs2-tools and ocfs2console packages.
For Red Hat's RHEL4, download and install the appropriate module
package and the two tools packages, ocfs2-tools and ocfs2console.
Appropriate module refers to one matching the kernel version,
flavor and architecture. Flavor refers to smp, hugemem, etc.
Q02 What are the latest versions of the OCFS2 packages?
A02 The latest module package version is 1.2.2. The latest tools/console
packages versions are 1.2.1.
Q03 How do I interpret the package name
ocfs2-2.6.9-22.0.1.ELsmp-1.2.1-1.i686.rpm?
A03 The package name is comprised of multiple parts separated by '-'.
a) ocfs2 - Package name
b) 2.6.9-22.0.1.ELsmp - Kernel version and flavor
c) 1.2.1 - Package version
d) 1 - Package subversion
e) i686 - Architecture
Q04 How do I know which package to install on my box?
A04 After one identifies the package name and version to install,
one still needs to determine the kernel version, flavor and
architecture.
To know the kernel version and flavor, do:
# uname -r
2.6.9-22.0.1.ELsmp
To know the architecture, do:
# rpm -qf /boot/vmlinuz-`uname -r` --queryformat "%{ARCH}\n"
i686
Q05 Why can't I use "uname -p" to determine the kernel architecture?
A05 "uname -p" does not always provide the exact kernel architecture.
Case in point the RHEL3 kernels on x86_64. Even though Red Hat has
two different kernel architectures available for this port, ia32e
and x86_64, "uname -p" identifies both as the generic "x86_64".
Q06 How do I install the rpms?
A06 First install the tools and console packages:
# rpm -Uvh ocfs2-tools-1.2.1-1.i386.rpm ocfs2console-1.2.1-1.i386.rpm
Then install the appropriate kernel module package:
# rpm -Uvh ocfs2-2.6.9-22.0.1.ELsmp-1.2.1-1.i686.rpm
Q07 Do I need to install the console?
A07 No, the console is not required but recommended for ease-of-use.
Q08 What are the dependencies for installing ocfs2console?
A08 ocfs2console requires e2fsprogs, glib2 2.2.3 or later, vte 0.11.10 or
later, pygtk2 (EL4) or python-gtk (SLES9) 1.99.16 or later,
python 2.3 or later and ocfs2-tools.
Q09 What modules are installed with the OCFS2 1.2 package?
A09 a) configfs.ko
b) ocfs2.ko
c) ocfs2_dlm.ko
d) ocfs2_dlmfs.ko
e) ocfs2_nodemanager.ko
f) debugfs
Q10 What tools are installed with the ocfs2-tools 1.2 package?
A10 a) mkfs.ocfs2
b) fsck.ocfs2
c) tunefs.ocfs2
d) debugfs.ocfs2
e) mount.ocfs2
f) mounted.ocfs2
g) ocfs2cdsl
h) ocfs2_hb_ctl
i) o2cb_ctl
j) o2cb - init service to start/stop the cluster
k) ocfs2 - init service to mount/umount ocfs2 volumes
l) ocfs2console - installed with the console package
Q11 What is debugfs and is it related to debugfs.ocfs2?
A11 debugfs is an in-memory filesystem developed by Greg Kroah-Hartman.
It is useful for debugging as it allows kernel space to easily
export data to userspace. For more, http://kerneltrap.org/node/4394.
It is currently being used by OCFS2 to dump the list of
filesystem locks and could be used for more in the future.
It is bundled with OCFS2 as the various distributions are currently
not bundling it.
While debugfs and debugfs.ocfs2 are unrelated in general, the
latter is used as the front-end for the debugging info provided
by the former. For example, refer to the troubleshooting section.
==============================================================================
Configure
---------
Q01 How do I populate /etc/ocfs2/cluster.conf?
A01 If you have installed the console, use it to create this
configuration file. For details, refer to the user's guide.
If you do not have the console installed, check the Appendix in the
User's guide for a sample cluster.conf and the details of all the
components.
Do not forget to copy this file to all the nodes in the cluster.
If you ever edit this file on any node, ensure the other nodes are
updated as well.
Q02 Should the IP interconnect be public or private?
A02 Using a private interconnect is recommended. While OCFS2 does not
take much bandwidth, it does require the nodes to be alive on the
network and sends regular keepalive packets to ensure that they are.
To avoid a network delay being interpreted as a node disappearing on
the net which could lead to a node-self-fencing, a private interconnect
is recommended. One could use the same interconnect for Oracle RAC
and OCFS2.
Q03 What should the node name be and should it be related to the IP
address?
A03 The node name needs to match the hostname. The IP address need
not be the one associated with that hostname. As in, any valid
IP address on that node can be used. OCFS2 will not attempt to
match the node name (hostname) with the specified IP address.
Q04 How do I modify the IP address, port or any other information
specified in cluster.conf?
A04 While one can use ocfs2console to add nodes dynamically to a running
cluster, any other modifications require the cluster to be offlined.
Stop the cluster on all nodes, edit /etc/ocfs2/cluster.conf on one
and copy to the rest, and restart the cluster on all nodes. Always
ensure that cluster.conf is the same on all the nodes in the cluster.
==============================================================================
O2CB Cluster Service
--------------------
Q01 How do I configure the cluster service?
A01 # /etc/init.d/o2cb configure
Enter 'y' if you want the service to load on boot and the name of
the cluster (as listed in /etc/ocfs2/cluster.conf).
Q02 How do I start the cluster service?
A02 a) To load the modules, do:
# /etc/init.d/o2cb load
b) To Online it, do:
# /etc/init.d/o2cb online [cluster_name]
If you have configured the cluster to load on boot, you could
combine the two as follows:
# /etc/init.d/o2cb start [cluster_name]
The cluster name is not required if you have specified the name
during configuration.
Q03 How do I stop the cluster service?
A03 a) To offline it, do:
# /etc/init.d/o2cb offline [cluster_name]
b) To unload the modules, do:
# /etc/init.d/o2cb unload
If you have configured the cluster to load on boot, you could
combine the two as follows:
# /etc/init.d/o2cb stop [cluster_name]
The cluster name is not required if you have specified the name
during configuration.
Q04 How can I learn the status of the cluster?
A04 To learn the status of the cluster, do:
# /etc/init.d/o2cb status
Q05 I am unable to get the cluster online. What could be wrong?
A05 Check whether the node name in the cluster.conf exactly matches the
hostname. One of the nodes in the cluster.conf need to be in the
cluster for the cluster to be online.
==============================================================================
Format
------
Q01 How do I format a volume?
A01 You could either use the console or use mkfs.ocfs2 directly to format
the volume. For console, refer to the user's guide.
# mkfs.ocfs2 -L "oracle_home" /dev/sdX
The above formats the volume with default block and cluster sizes,
which are computed based upon the size of the volume.
# mkfs.ocfs2 -b 4k -C 32K -L "oracle_home" -N 4 /dev/sdX
The above formats the volume for 4 nodes with a 4K block size and a
32K cluster size.
Q02 What does the number of node slots during format refer to?
A02 The number of node slots specifies the number of nodes that can
concurrently mount the volume. This number is specified during
format and can be increased using tunefs.ocfs2. This number cannot
be decreased.
Q03 What should I consider when determining the number of node slots?
A03 OCFS2 allocates system files, like Journal, for each node slot.
So as to not to waste space, one should specify a number within the
ballpark of the actual number of nodes. Also, as this number can be
increased, there is no need to specify a much larger number than one
plans for mounting the volume.
Q04 Does the number of node slots have to be the same for all volumes?
A04 No. This number can be different for each volume.
Q05 What block size should I use?
A05 A block size is the smallest unit of space addressable by the file
system. OCFS2 supports block sizes of 512 bytes, 1K, 2K and 4K.
The block size cannot be changed after the format. For most volume
sizes, a 4K size is recommended. On the other hand, the 512 bytes
block is never recommended.
Q06 What cluster size should I use?
A06 A cluster size is the smallest unit of space allocated to a file to
hold the data. OCFS2 supports cluster sizes of 4K, 8K, 16K, 32K,
64K, 128K, 256K, 512K and 1M. For database volumes, a cluster size
of 128K or larger is recommended. For Oracle home, 32K to 64K.
Q07 Any advantage of labelling the volumes?
A07 As in a shared disk environment, the disk name (/dev/sdX) for a
particular device be different on different nodes, labelling becomes
a must for easy identification.
You could also use labels to identify volumes during mount.
# mount -L "label" /dir
The volume label is changeable using the tunefs.ocfs2 utility.
==============================================================================
Mount
-----
Q01 How do I mount the volume?
A01 You could either use the console or use mount directly. For console,
refer to the user's guide.
# mount -t ocfs2 /dev/sdX /dir
The above command will mount device /dev/sdX on directory /dir.
Q02 How do I mount by label?
A02 To mount by label do:
# mount -L "label" /dir
Q03 What entry to I add to /etc/fstab to mount an ocfs2 volume?
A03 Add the following:
/dev/sdX /dir ocfs2 noauto,_netdev 0 0
The _netdev option indicates that the devices needs to be mounted after
the network is up.
Q04 What do I need to do to mount OCFS2 volumes on boot?
A04 a) Enable o2cb service using:
# chkconfig --add o2cb
b) Enable ocfs2 service using:
# chkconfig --add ocfs2
c) Configure o2cb to load on boot using:
# /etc/init.d/o2cb configure
d) Add entries into /etc/fstab as follows:
/dev/sdX /dir ocfs2 _netdev 0 0
Q05 How do I know my volume is mounted?
A05 a) Enter mount without arguments, or
# mount
b) List /etc/mtab, or
# cat /etc/mtab
c) List /proc/mounts, or
# cat /proc/mounts
d) Runs ocfs2 service
# /etc/init.d/ocfs2 status
mount command reads the /etc/mtab to show the information.
Q06 What are the /config and /dlm mountpoints for?
A06 OCFS2 comes bundled with two in-memory filesystems configfs and
ocfs2_dlmfs. configfs is used by the ocfs2 tools to communicate to the
in-kernel node manager the list of nodes in the cluster and to the
in-kernel heartbeat thread the resource to heartbeat on.
ocfs2_dlmfs is used by ocfs2 tools to communicate with the in-kernel
dlm to take and release clusterwide locks on resources.
Q07 Why does it take so much time to mount the volume?
A07 It takes around 5 secs for a volume to mount. It does so so as
to let the heartbeat thread stabilize. In a later release, we
plan to add support for a global heartbeat, which will make most
mounts instant.
==============================================================================
Oracle RAC
----------
Q01 Any special flags to run Oracle RAC?
A01 OCFS2 volumes containing the Voting diskfile (CRS), Cluster registry
(OCR), Data files, Redo logs, Archive logs and control files must
be mounted with the "datavolume" and "nointr" mount options. The
datavolume option ensures that the Oracle processes opens these files
with the o_direct flag. The "nointr" option ensures that the ios
are not interrupted by signals.
# mount -o datavolume,nointr -t ocfs2 /dev/sda1 /u01/db
Q02 What about the volume containing Oracle home?
A02 Oracle home volume should be mounted normally, that is, without the
"datavolume" and "nointr" mount options. These mount options are only
relevant for Oracle files listed above.
# mount -t ocfs2 /dev/sdb1 /software/orahome
Q03 Does that mean I cannot have my data file and Oracle home on the
same volume?
A03 Yes. The volume containing the Oracle data files, redo-logs, etc.
should never be on the same volume as the distribution (including the
trace logs like, alert.log).
==============================================================================
Moving data from OCFS (Release 1) to OCFS2
------------------------------------------
Q01 Can I mount OCFS volumes as OCFS2?
A01 No. OCFS and OCFS2 are not on-disk compatible. We had to break the
compatibility in order to add many of the new features. At the same
time, we have added enough flexibility in the new disk layout so as to
maintain backward compatibility in the future.
Q02 Can OCFS volumes and OCFS2 volumes be mounted on the same machine
simultaneously?
A02 No. OCFS only works on 2.4 linux kernels (Red Hat's AS2.1/EL3 and SuSE's
SLES8). OCFS2, on the other hand, only works on the 2.6 kernels
(Red Hat's EL4 and SuSE's SLES9).
Q03 Can I access my OCFS volume on 2.6 kernels (SLES9/RHEL4)?
A03 Yes, you can access the OCFS volume on 2.6 kernels using FSCat
tools, fsls and fscp. These tools can access the OCFS volumes at the
device layer, to list and copy the files to another filesystem.
FSCat tools are available on oss.oracle.com.
Q04 Can I in-place convert my OCFS volume to OCFS2?
A04 No. The on-disk layout of OCFS and OCFS2 are sufficiently different
that it would require a third disk (as a temporary buffer) inorder to
in-place upgrade the volume. With that in mind, it was decided not to
develop such a tool but instead provide tools to copy data from OCFS
without one having to mount it.
Q05 What is the quickest way to move data from OCFS to OCFS2?
A05 Quickest would mean having to perform the minimal number of copies.
If you have the current backup on a non-OCFS volume accessible from
the 2.6 kernel install, then all you would need to do is to retore
the backup on the OCFS2 volume(s). If you do not have a backup but
have a setup in which the system containing the OCFS2 volumes can
access the disks containing the OCFS volume, you can use the FSCat
tools to extract data from the OCFS volume and copy onto OCFS2.
==============================================================================
Coreutils
---------
Q01 Like with OCFS (Release 1), do I need to use o_direct enabled tools
to perform cp, mv, tar, etc.?
A01 No. OCFS2 does not need the o_direct enabled tools. The file system
allows processes to open files in both o_direct and bufferred mode
concurrently.
==============================================================================
Troubleshooting
---------------
Q01 How do I enable and disable filesystem tracing?
A01 To list all the debug bits along with their statuses, do:
# debugfs.ocfs2 -l
To enable tracing the bit SUPER, do:
# debugfs.ocfs2 -l SUPER allow
To disable tracing the bit SUPER, do:
# debugfs.ocfs2 -l SUPER off
To totally turn off tracing the SUPER bit, as in, turn off
tracing even if some other bit is enabled for the same, do:
# debugfs.ocfs2 -l SUPER deny
To enable heartbeat tracing, do:
# debugfs.ocfs2 -l HEARTBEAT ENTRY EXIT allow
To disable heartbeat tracing, do:
# debugfs.ocfs2 -l HEARTBEAT off ENTRY EXIT deny
Q02 How do I get a list of filesystem locks and their statuses?
A02 OCFS2 1.0.9+ has this feature. To get this list, do:
a) Mount debugfs is mounted at /debug.
# mount -t debugfs debugfs /debug
b) Dump the locks.
# echo "fs_locks" | debugfs.ocfs2 /dev/sdX >/tmp/fslocks
Q03 How do I read the fs_locks output?
A03 Let's look at a sample output:
Lockres: M000000000000000006672078b84822 Mode: Protected Read
Flags: Initialized Attached
RO Holders: 0 EX Holders: 0
Pending Action: None Pending Unlock Action: None
Requested Mode: Protected Read Blocking Mode: Invalid
First thing to note is the Lockres, which is the lockname. The
dlm identifies resources using locknames. The lockname is a
combination of a lock type (S superblock, M metadata, D filedata,
R rename, W readwrite), inode number and generation.
To get the inode number and generation from lockname, do:
#echo "stat <M000000000000000006672078b84822>" | debugfs.ocfs2 /dev/sdX
Inode: 419616 Mode: 0666 Generation: 2025343010 (0x78b84822)
....
To map the lockname to a directory entry, do:
# echo "locate <M000000000000000006672078b84822>" | debugfs.ocfs2 /dev/sdX
debugfs.ocfs2 1.2.0
debugfs: 419616 /linux-2.6.15/arch/i386/kernel/semaphore.c
One could also provide the inode number instead of the lockname.
# echo "locate <419616>" | debugfs.ocfs2 /dev/sdX
debugfs.ocfs2 1.2.0
debugfs: 419616 /linux-2.6.15/arch/i386/kernel/semaphore.c
To get a lockname from a directory entry, do:
# echo "encode /linux-2.6.15/arch/i386/kernel/semaphore.c" |
debugfs.ocfs2 /dev/sdX
M000000000000000006672078b84822 D000000000000000006672078b84822
W000000000000000006672078b84822
The first is the Metadata lock, then Data lock and last
ReadWrite lock for the same resource.
The DLM supports 3 lock modes: NL no lock, PR protected read and
EX exclusive.
If you have a dlm hang, the resource to look for would be one
with the "Busy" flag set.
The next step would be to query the dlm for the lock resource.
Note: The dlm debugging is still a work in progress.
To do dlm debugging, first one needs to know the dlm domain,
which matches the volume UUID.
# echo "stats" | debugfs.ocfs2 -n /dev/sdX | grep UUID: |
while read a b ; do echo $b ; done
82DA8137A49A47E4B187F74E09FBBB4B
Then do:
# echo R dlm_domain lockname > /proc/fs/ocfs2_dlm/debug
For example:
# echo R 82DA8137A49A47E4B187F74E09FBBB4B
M000000000000000006672078b84822 > /proc/fs/ocfs2_dlm/debug
# dmesg | tail
struct dlm_ctxt: 82DA8137A49A47E4B187F74E09FBBB4B, node=75, key=965960985
lockres: M000000000000000006672078b84822, owner=79, state=0 last used: 0, on purge list: no
granted queue:
type=3, conv=-1, node=79, cookie=11673330234144325711, ast=(empty=y,pend=n), bast=(empty=y,pend=n)
converting queue:
blocked queue:
It shows that the lock is mastered by node 75 and that node 79
has been granted a PR lock on the resource.
This is just to give a flavor of dlm debugging.
==============================================================================
Limits
------
Q01 Is there a limit to the number of subdirectories in a directory?
A01 Yes. OCFS2 currently allows up to 32000 subdirectories. While this
limit could be increased, we will not be doing it till we
implement some kind of efficient name lookup (htree, etc.).
Q02 Is there a limit to the size of an ocfs2 file system?
A02 Yes, current software addresses block numbers with 32 bits. So the
file system device is limited to (2 ^ 32) * blocksize (see mkfs -b).
With a 4KB block size this amounts to a 16TB file system. This block
addressing limit will be relaxed in future software. At that point
the limit becomes addressing clusters of 1MB each with 32 bits which
leads to a 4PB file system.
==============================================================================
System Files
------------
Q01 What are system files?
A01 System files are used to store standard filesystem metadata like
bitmaps, journals, etc. Storing this information in files in a
directory allows OCFS2 to be extensible. These system files
can be accessed using debugfs.ocfs2.
To list the system files, do:
# echo "ls -l //" | debugfs.ocfs2 /dev/sdX
18 16 1 2 .
18 16 2 2 ..
19 24 10 1 bad_blocks
20 32 18 1 global_inode_alloc
21 20 8 1 slot_map
22 24 9 1 heartbeat
23 28 13 1 global_bitmap
24 28 15 2 orphan_dir:0000
25 32 17 1 extent_alloc:0000
26 28 16 1 inode_alloc:0000
27 24 12 1 journal:0000
28 28 16 1 local_alloc:0000
29 3796 17 1 truncate_log:0000
The first column lists the block number.
Q02 Why do some files have numbers at the end?
A02 There are two types of files, global and local. Global files are
for all the nodes, while local, like journal:0000, are node specific.
The set of local files used by a node is determined by the slot
mapping of that node. The numbers at the end of the system file
name is the slot#.
To list the slot maps, do:
# echo "slotmap" | debugfs.ocfs2 -n /dev/sdX
Slot# Node#
0 39
1 40
2 41
3 42
==============================================================================
Heartbeat
---------
Q01 How does the disk heartbeat work?
A01 Every node writes every two secs to its block in the heartbeat
system file. The block offset is equal to its global node
number. So node 0 writes to the first block, node 1 to the
second, etc. All the nodes also read the heartbeat sysfile every
two secs. As long as the timestamp is changing, that node is
deemed alive.
Q02 When is a node deemed dead?
A02 An active node is deemed dead if it does not update its
timestamp for O2CB_HEARTBEAT_THRESHOLD (default=7) loops. Once a node
is deemed dead, the surviving node which manages to cluster lock the
dead node's journal, recovers it by replaying the journal.
Q03 What about self fencing?
A03 A node self-fences if it fails to update its timestamp for
((O2CB_HEARTBEAT_THRESHOLD - 1) * 2) secs. The [o2hb-xx] kernel
thread, after every timestamp write, sets a timer to panic the system
after that duration. If the next timestamp is written within that
duration, as it should, it first cancels that timer before setting
up a new one. This way it ensures the system will self fence if for
some reason the [o2hb-x] kernel thread is unable to update the
timestamp and thus be deemed dead by other nodes in the cluster.
Q04 How can one change the parameter value of O2CB_HEARTBEAT_THRESHOLD?
A04 This parameter value could be changed by adding it to
/etc/sysconfig/o2cb and RESTARTING the O2CB cluster. This value should
be the SAME on ALL the nodes in the cluster.
Q05 What should one set O2CB_HEARTBEAT_THRESHOLD to?
A05 It should be set to the timeout value of the io layer. Most
multipath solutions have a timeout ranging from 60 secs to
120 secs. For 60 secs, set it to 31. For 120 secs, set it to 61.
O2CB_HEARTBEAT_THRESHOLD = (((timeout in secs) / 2) + 1)
Q06 What if a node umounts a volume?
A06 During umount, the node will broadcast to all the nodes that
have mounted that volume to drop that node from its node maps.
As the journal is shutdown before this broadcast, any node crash
after this point is ignored as there is no need for recovery.
Q07 I encounter "Kernel panic - not syncing: ocfs2 is very sorry to
be fencing this system by panicing" whenever I run a heavy io
load?
A07 We have encountered a bug with the default "cfq" io scheduler
which causes a process doing heavy io to temporarily starve out
other processes. While this is not fatal for most environments,
it is for OCFS2 as we expect the hb thread to be r/w to the hb
area atleast once every 12 secs (default).
Bug with the fix has been filed with Red Hat and Novell. For
more, refer to the tracker bug filed on bugzilla:
http://oss.oracle.com/bugzilla/show_bug.cgi?id=671
Till this issue is resolved, one is advised to use the
"deadline" io scheduler. To use deadline, add "elevator=deadline"
to the kernel command line as follows:
1. For SLES9, edit the command line in /boot/grub/menu.lst.
title Linux 2.6.5-7.244-bigsmp elevator=deadline
kernel (hd0,4)/boot/vmlinuz-2.6.5-7.244-bigsmp root=/dev/sda5
vga=0x314 selinux=0 splash=silent resume=/dev/sda3
elevator=deadline showopts console=tty0
console=ttyS0,115200 noexec=off
initrd (hd0,4)/boot/initrd-2.6.5-7.244-bigsmp
2. For RHEL4, edit the command line in /boot/grub/grub.conf:
title Red Hat Enterprise Linux AS (2.6.9-22.EL)
root (hd0,0)
kernel /vmlinuz-2.6.9-22.EL ro root=LABEL=/ console=ttyS0,115200
console=tty0 elevator=deadline noexec=off
initrd /initrd-2.6.9-22.EL.img
To see the current kernel command line, do:
# cat /proc/cmdline
==============================================================================
Quorum and Fencing
------------------
Q01 What is a quorum?
A01 A quorum is a designation given to a group of nodes in a cluster which
are still allowed to operate on shared storage. It comes up when
there is a failure in the cluster which breaks the nodes up
into groups which can communicate in their groups and with the
shared storage but not between groups.
Q02 How does OCFS2's cluster services define a quorum?
A02 The quorum decision is made by a single node based on the number
of other nodes that are considered alive by heartbeating and the number
of other nodes that are reachable via the network.
A node has quorum when:
* it sees an odd number of heartbeating nodes and has network
connectivity to more than half of them.
or
* it sees an even number of heartbeating nodes and has network
connectivity to at least half of them *and* has connectivity to
the heartbeating node with the lowest node number.
Q03 What is fencing?
A03 Fencing is the act of forecefully removing a node from a cluster.
A node with OCFS2 mounted will fence itself when it realizes that it
doesn't have quorum in a degraded cluster. It does this so that other
nodes won't get stuck trying to access its resources. Currently OCFS2
will panic the machine when it realizes it has to fence itself
off from the cluster. As described in Q02, it will do this when it
sees more nodes heartbeating than it has connectivity to and fails
the quorum test.
Q04 How does a node decide that it has connectivity with another?
A04 When a node sees another come to life via heartbeating it will try
and establish a TCP connection to that newly live node. It considers
that other node connected as long as the TCP connection persists and
the connection is not idle for 10 seconds. Once that TCP connection
is closed or idle it will not be reestablished until heartbeat thinks
the other node has died and come back alive.
Q05 How long does the quorum process take?
A05 First a node will realize that it doesn't have connectivity with
another node. This can happen immediately if the connection is closed
but can take a maximum of 10 seconds of idle time. Then the node
must wait long enough to give heartbeating a chance to declare the
node dead. It does this by waiting two iterations longer than
the number of iterations needed to consider a node dead (see Q03 in
the Heartbeat section of this FAQ). The current default of 7
iterations of 2 seconds results in waiting for 9 iterations or 18
seconds. By default, then, a maximum of 28 seconds can pass from the
time a network fault occurs until a node fences itself.
Q06 How can one avoid a node from panic-ing when one shutdowns the other
node in a 2-node cluster?
A06 This typically means that the network is shutting down before all the
OCFS2 volumes are being umounted. Ensure the ocfs2 init script is
enabled. This script ensures that the OCFS2 volumes are umounted before
the network is shutdown.
To check whether the service is enabled, do:
# chkconfig --list ocfs2
ocfs2 0:off 1:off 2:on 3:on 4:on 5:on 6:off
Q07 How does one list out the startup and shutdown ordering of the
OCFS2 related services?
A07 To list the startup order for runlevel 3 on RHEL4, do:
# cd /etc/rc3.d
# ls S*ocfs2* S*o2cb* S*network*
S10network S24o2cb S25ocfs2
To list the shutdown order on RHEL4, do:
# cd /etc/rc6.d
# ls K*ocfs2* K*o2cb* K*network*
K19ocfs2 K20o2cb K90network
To list the startup order for runlevel 3 on SLES9, do:
# cd /etc/init.d/rc3.d
# ls S*ocfs2* S*o2cb* S*network*
S05network S07o2cb S08ocfs2
To list the shutdown order on SLES9, do:
# cd /etc/init.d/rc3.d
# ls K*ocfs2* K*o2cb* K*network*
K14ocfs2 K15o2cb K17network
Please note that the default ordering in the ocfs2 scripts only include
the network service and not any shared-device specific service, like
iscsi. If one is using iscsi or any shared device requiring a service
to be started and shutdown, please ensure that that service runs before
and shutsdown after the ocfs2 init service.
==============================================================================
Novell SLES9
------------
Q01 Why are OCFS2 packages for SLES9 not made available on oss.oracle.com?
A01 OCFS2 packages for SLES9 are available directly from Novell as
part of the kernel. Same is true for the various Asianux
distributions and for ubuntu. As OCFS2 is now part of the
mainline kernel (http://lwn.net/Articles/166954/), we expect more
distributions to bundle the product with the kernel.
Q02 What versions of OCFS2 are available with SLES9 and how do they
match with the Red Hat versions available on oss.oracle.com?
A02 As both Novell and Oracle ship OCFS2 on different schedules, the
package versions do not match. We expect to resolve itself over
time as the number of patch fixes reduce.
Novell is shipping two SLES9 releases, viz., SP2 and SP3.
The latest kernel with the SP2 release is 2.6.5-7.202.7. It ships
with OCFS2 1.0.8.
The latest kernel with the SP3 release is 2.6.5-7.257. It ships
with OCFS2 1.2.1.
==============================================================================
What's New in 1.2
-----------------
Q01 What is new in OCFS2 1.2?
A01 OCFS2 1.2 has two new features:
a) It is endian-safe. With this release, one can mount the same
volume concurrently on x86, x86-64, ia64 and big endian architectures
ppc64 and s390x.
b) Supports readonly mounts. The fs uses this feature to auto
remount ro when encountering on-disk corruptions (instead of
panic-ing).
Q02 Do I need to re-make the volume when upgrading?
A02 No. OCFS2 1.2 is fully on-disk compatible with 1.0.
Q03 Do I need to upgrade anything else?
A03 Yes, the tools needs to be upgraded to ocfs2-tools 1.2.
ocfs2-tools 1.0 will not work with OCFS2 1.2 nor will 1.2
tools work with 1.0 modules.
==============================================================================
Upgrading to the latest release
-------------------------------
Q01 How do I upgrade to the latest release?
A01 1. Download the latest ocfs2-tools and ocfs2console for the target
platform and the appropriate ocfs2 module package for the kernel version,
flavor and architecture. (For more, refer to the "Download and Install"
section above.)
2. Umount all OCFS2 volumes.
# umount -at ocfs2
3. Shutdown the cluster and unload the modules.
# /etc/init.d/o2cb offline
# /etc/init.d/o2cb unload
4. If required, upgrade the tools and console.
# rpm -Uvh ocfs2-tools-1.2.1-1.i386.rpm ocfs2console-1.2.1-1.i386.rpm
5. Upgrade the module.
# rpm -Uvh ocfs2-2.6.9-22.0.1.ELsmp-1.2.2-1.i686.rpm
6. Ensure init services ocfs2 and o2cb are enabled.
# chkconfig --add o2cb
# chkconfig --add ocfs2
7. To check whether the services are enabled, do:
# chkconfig --list o2cb
o2cb 0:off 1:off 2:on 3:on 4:on 5:on 6:off
# chkconfig --list ocfs2
ocfs2 0:off 1:off 2:on 3:on 4:on 5:on 6:off
8. At this stage one could either reboot the node or simply, restart
the cluster and mount the volume.
Q02 Can I do a rolling upgrade from 1.0.x/1.2.x to 1.2.2?
A02 Rolling upgrade to 1.2.2 is not recommended. Shutdown the cluster on
all nodes before upgrading the nodes.
Q03 After upgrade I am getting the following error on mount
"mount.ocfs2: Invalid argument while mounting /dev/sda6 on /ocfs".
A03 Do "dmesg | tail". If you see the error:
>> ocfs2_parse_options:523 ERROR: Unrecognized mount option
>> "heartbeat=local" or missing value
it means that you are trying to use the 1.2 tools and 1.0
modules. Ensure that you have unloaded the 1.0 modules and
installed and loaded the 1.2 modules. Use modinfo to determine
the version of the module installed and/or loaded.
Q04 The cluster fails to load. What do I do?
A04 Check "demsg | tail" for any relevant errors. One common error
is as follows:
>> SELinux: initialized (dev configfs, type configfs), not configured for labeling
>> audit(1139964740.184:2): avc: denied { mount } for ...
The above error indicates that you have SELinux activated. A bug
in SELinux does not allow configfs to mount. Disable SELinux
by setting "SELINUX=disabled" in /etc/selinux/config. Change
is activated on reboot.
==============================================================================
Processes
---------
Q01 List and describe all OCFS2 threads?
A01 [o2net]
One per node. Is a workqueue thread started when the cluster is
brought online and stopped when offline. It handles the network
communication for all threads. It gets the list of active nodes
from the o2hb thread and sets up tcp/ip communication channels
with each active node. It sends regular keepalive packets to
detect any interruption on the channels.
[user_dlm]
One per node. Is a workqueue thread started when dlmfs is loaded and
stopped on unload. (dlmfs is an in-memory file system which allows user
space processes to access the dlm in kernel to lock and unlock
resources.) Handles lock downconverts when requested by other
nodes.
[ocfs2_wq]
One per node. Is a workqueue thread started when ocfs2 module is
loaded and stopped on unload. Handles blockable file system tasks
like truncate log flush, orphan dir recovery and local alloc
recovery, which involve taking dlm locks. Various code paths
queue tasks to this thread. For example, ocfs2rec queues orphan
dir recovery so that while the task is kicked off as part of
recovery, its completion does not affect the recovery time.
[o2hb-14C29A7392]
One per heartbeat device. Is a kernel thread started when the
heartbeat region is populated in configfs and stopped when it
is removed. It writes every 2 secs to its block in the heartbeat
region to indicate to other nodes that that node is alive. It also
reads the region to maintain a nodemap of live nodes. It notifies
o2net and dlm any changes in the nodemap.
[ocfs2vote-0]
One per mount. Is a kernel thread started when a volume is mounted
and stopped on umount. It downgrades locks when requested by other
nodes in reponse to blocking ASTs (BASTs). It also fixes up the dentry
cache in reponse to files unlinked or renamed on other nodes.
[dlm_thread]
One per dlm domain. Is a kernel thread started when a dlm domain
is created and stopped when destroyed. This is the core dlm
which maintains the list of lock resources and handles the
cluster locking infrastructure.
[dlm_reco_thread]
One per dlm domain. Is a kernel thread which handles dlm recovery
whenever a node dies. If the node is the dlm recovery master, it
remasters all the locks owned by the dead node.
[dlm_wq]
One per dlm domain. Is a workqueue thread. o2net queues dlm
tasks on this thread.
[kjournald]
One per mount. Is used as OCFS2 uses JDB for journalling.
[ocfs2cmt-0]
One per mount. Is a kernel thread started when a volume is
mounted and stooped on umount. Works in conjunction with
kjournald.
[ocfs2rec-0]
Is started whenever another node needs to be be recovered. This
could be either on mount when it discovers a dirty journal or
during operation when hb detects a dead node. ocfs2rec handles
the file system recovery and it runs after the dlm has finished
its recovery.
==============================================================================
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