<html> <head> <meta http-equiv="content-type" content="text/html; charset=UTF-8"> <title>dvdisaster</title> <link rel="stylesheet" type="text/css" href="../include/dvdisaster.css"> </head> <body> <!--- Title header ---> <table width="100%" cellpadding="0" border="0"> <tr> <td align="left"> <font size="+3"><b>dvdisaster</b></font> <i>Version 0.72 (pl1)</i> </td> <td align="right"> <font size="+3"> </font><a href="http://dvdisaster.net/en/">To the Internet version</a> <a href="../de/howtos13.html"></a> <a href="../ru/howtos13.html"></a> </td> </tr> </table> <!--- Language chooser or separator ---> <table width="100%" cellpadding="0" border="0"> <tr bgcolor="#000000"> <td colspan="2" width="100%"><img width=1 height=1 alt=""></td> </tr> <tr><td colspan="2" width="100%" height="10"> <img width=1 height=1 alt=""> </td></tr> </table> <!--- Main body (Navigation, actual page content, optional news column) ---> <table width="100%" cellspacing=0> <tr> <!--- Navigation ---> <td bgcolor="#f0f0f0" valign="top" width="20%"> <table width="100%" cellpadding="10"> <tr> <td> <font size="-1"><b>Contents</b></font> <table width="100%" cellpadding="0" cellspacing="0"> <tr bgcolor="#000000"> <td width="100%"><img width=1 height=1 alt=""></td> </tr> </table><p> <table width="100%"> <tr><td colspan=3><font size="-1"><a href="news.html">News</a></font></td></tr> <tr><td></td><td></td><td height="10"></td></tr> <tr><td colspan=3><font size="-1"><a href="index.html">Overview</a></font></td></tr> <tr><td></td><td></td><td height="10"></td></tr> <tr><td colspan=3><font size="-1"><a href="howtos.html">Howtos</a></font></td></tr> <tr><td valign="top" width="1%">·</td><td colspan=2><font size="-1"><a href="howtos60.html">The big picture</a></font></td></tr> <tr><td valign="top" width="1%">·</td><td colspan=2><font size="-1"><a href="howtos10.html">Scanning media for errors</a></font></td></tr> <tr><td valign="top"></td><td>-</td><td><font size="-1"><a href="howtos11.html">Basic settings</a></font></td></tr> <tr><td valign="top"></td><td>-</td><td><font size="-1"><a href="howtos12.html">Performing the test</a></font></td></tr> <tr><td valign="top"></td><td>-</td><td><font size="-1">Interpreting the results</font></td></tr> <tr><td valign="top"></td><td>-</td><td><font size="-1"><a href="howtos14.html">Advanced settings</a></font></td></tr> <tr><td valign="top" width="1%">·</td><td colspan=2><font size="-1"><a href="howtos20.html">Putting error correction data on a separate file</a></font></td></tr> <tr><td valign="top" width="1%">·</td><td colspan=2><font size="-1"><a href="howtos30.html">Putting error correction data on the medium</a></font></td></tr> <tr><td valign="top" width="1%">·</td><td colspan=2><font size="-1"><a href="howtos40.html">Recovering media images</a></font></td></tr> <tr><td valign="top" width="1%">·</td><td colspan=2><font size="-1"><a href="howtos50.html">Getting information about images and error correction data</a></font></td></tr> <tr><td valign="top" width="1%">·</td><td colspan=2><font size="-1"><a href="howtos90.html">Testing image compatibility</a></font></td></tr> <tr><td valign="top" width="1%">·</td><td colspan=2><font size="-1"><a href="howtosa0.html">Dialogs and buttons</a></font></td></tr> <tr><td></td><td></td><td height="10"></td></tr> <tr><td colspan=3><font size="-1"><a href="download.html">Download</a></font></td></tr> <tr><td></td><td></td><td height="10"></td></tr> <tr><td colspan=3><font size="-1"><a href="qa.html">Questions and Answers</a></font></td></tr> <tr><td></td><td></td><td height="10"></td></tr> <tr><td colspan=3><font size="-1"><a href="feedback.html">Bug reporting</a></font></td></tr> </table> </td> </tr> </table> </td> <td></td> <!--- Actual page contents ---> <td valign="top" width="77%" rowspan="2"> <table width="100%" bgcolor="#f0f0f0"> <tr><td><font size="+1"><b>Scanning media for errors</b></font></td> <td rowspan="2" align="right"><img src="images/scan-icon.png"></td></tr> <tr><td><i>Interpreting results</i></td></tr> </table><p> <!--- Insert actual page content below ---> <!--- begin of screen shot ---> <table> <tr> <td valign="top"> <b>Overview.</b> dvdisaster provides several information about the scanning results: <ul> <li>The spiral under "<b>Medium State</b>" (to the right).<p> The spiral provides information about the medium readability. The medium is fully readable when all segments of the spiral are colored green. Yellow or red blocks mark places where data could not be correctly read from the medium. The total number of unreadable sectors is printed in the <i>"Scanning finished:"</i> message at the window bottom.<p> </li> <li>"<b>Speed</b>" - The reading speed curve (upper left).<p> The reading speed is not an absolute gauge of the medium health, but it is usable as a rule of thumb: The more regular the curve, the better the medium. You will find examples of good and bad reading speed curves further down this page.<p></li> <li>"<b>C2 errors</b>" - A medium state gauge provided by the drive (down left).<p> This kind of analysis is <a href="qa_pipo.html">currently only available for CD media</a>. CD drives have a built-in error correction which can eliminate small data losses caused by minor defects on the medium. The number of C2 errors is a measurement of how often the drive needed to employ its internal error correction during the read - this value should be zero on good media.</li> </ul> </td> <td> <a name="snap1"></a> <table class="thumbnail" width="160px"> <tr><td><font size="-1">Overview</font></td></tr> <tr><td><a href="howtos13_expand=1.html#snap1"><img src="thumbnails/defective-cd.png"></a></td></tr> </table> </td> </tr> </table><p> <!--- end of screen shot ---> <b>Examples for good media</b><p> <!--- begin of screen shot ---> <table> <tr> <td valign="top"> <b>Good CD</b>: This screen shot shows a perfect CD: All blocks under "Medium state" are green, no C2 errors have been reported and the reading curve runs smoothly. A rising reading speed is normal for most media (see the next screen shot for a counter example). The small spikes at the beginning and at the end of the curve are normal; minor glitches like the one shown at 250M are also harmless. </td> <td> <a name="snap2"></a> <table class="thumbnail" width="160px"> <tr><td><font size="-1">Good CD</font></td></tr> <tr><td><a href="howtos13_expand=2.html#snap2"><img src="thumbnails/good-cd.png"></a></td></tr> </table> </td> </tr> </table><p> <!--- end of screen shot ---> <!--- begin of screen shot ---> <table> <tr> <td valign="top"> <b>Sometimes the reading curve won't rise steadily</b>: Multi-layered media might yield reading curves which are rising and dropping in a symmetric pattern. Not shown but also possible are flat curves without any change in reading speed (most typically seen with DVD-RAM). </td> <td> <a name="snap3"></a> <table class="thumbnail" width="160px"> <tr><td><font size="-1">Good two layered DVD</font></td></tr> <tr><td><a href="howtos13_expand=3.html#snap3"><img src="thumbnails/good-dvd9.png"></a></td></tr> </table> </td> </tr> </table><p> <!--- end of screen shot ---> <p> <b>An example for a weak medium</b><p> <!--- begin of screen shot ---> <table> <tr> <td valign="top"> This medium is still readable as indicated by the green spiral shown under "Medium state". However there are clear signs of serious trouble ahead: The drive must slow down significantly towards the end of the medium in order to read from it. Note the steep fall of reading speed after the 600M mark. This comes along with C2 error rates rising to the 100 mark; this is another warning that the medium is decaying in the outer region. If you have not created <a href="howtos20.html">error correction</a> data this is probably the last opportunity to do so as the medium will develop the first read errors soon. </td> <td> <a name="snap4"></a> <table class="thumbnail" width="160px"> <tr><td><font size="-1">Weak CD</font></td></tr> <tr><td><a href="howtos13_expand=4.html#snap4"><img src="thumbnails/weak-cd.png"></a></td></tr> </table> </td> </tr> </table><p> <!--- end of screen shot ---> <p> <b>Examples of defective media</b><p> <!--- begin of screen shot ---> <table class="screenshot"> <tr><td> <a name="snap5"></a> <b>Defective CD.</b> The red sectors in the spiral visualize large unreadable sections in the outer region of the medium. At the bottom of the window you will find the information that the medium contains 28752 unreadable sectors. This sums up to about 8.2% defective sectors (of 352486 sectors total) and is well within the <a href="howtos40.html">recovery</a> bounds by <a href="howtos20.html">error correction (ecc) data</a> made with default settings - if you have made the ecc data in time! Otherwise the contents of the red sectors are lost since ecc data cannot be created from already defective media. </td></tr> <tr><td align="center"> <a href="howtos13.html#snap5"> <img src="images/defective-cd.png"> </a> </td></tr> <tr><td align="center">Screen shot: Defective CD</td></tr> </table><pre> </pre> <!--- end of screen shot ---> <p> <a name="crc"></a> <!--- begin of screen shot ---> <table> <tr> <td valign="top"> <b>Checksum errors.</b> Yellow spots in the spiral depict places where the medium was fully readable, but the data read did not match checksums in the error correction data. There are two main causes: <p> <ul><li> <b>The image has been manipulated</b> after the creation of error correction data and before writing it to the medium. This can happen on Unix systems when the image is mounted with write access after ecc data has been created. Typical signs are CRC errors in sector 64 and in sectors 200 to 400 as the system updates the file access times there. Performing a data recovery using dvdisaster is typically harmless in this situation.<p> However if you have modified files in the image after creating the ecc data, the error correction data will be both worthless and dangerous. Applying a recovery to the medium will restore the image state at the time the ecc data has been created, and this will obviously not represent the most recent contents of the medium.<p></li> <li><b>There are technical problems with the computer system,</b> especially in mass storage communication. Perform the scan again and observe the CRC error locations. If CRC errors disappear or surface at different locations your system might have defective RAM, bad drive cabling/controllers or incorrect clock speeds.</li></ul> </td> <td> <a name="snap6"></a> <table class="thumbnail" width="160px"> <tr><td><font size="-1">Checksum errors</font></td></tr> <tr><td><a href="howtos13_expand=6.html#snap6"><img src="thumbnails/crc-cd.png"></a></td></tr> </table> </td> </tr> </table><p> <!--- end of screen shot ---> <p> </td> <!--- end of page contents ---> </tr> <tr valign="bottom"> <td bgcolor="#f0f0f0"> <table cellpadding="10"><tr><td><a href="http://dvdisaster.net/legacy/en/index.html"><font size="-1">Old documentation (V0.70)</font></a></td></tr></table> </td> <td></td> <td></td> </tr> </table> <!--- end of main body table ---> <!--- Page footer ---> <table width="100%" cellpadding="0" border="0"> <tr><td colspan="2" width="100%" height="10"><img width=1 height=1 alt=""></td> </tr> <tr bgcolor="#000000"><td colspan="2" width="100%"><img width=1 height=1 alt=""></td> </tr> <tr> <td align="center"> <font size="-1"> <i> Copyright 2004-2009 Carsten Gnörlich.<br> Verbatim copying and distribution of this entire article is permitted in any medium, provided this notice is preserved. </i> </font> </td> </tr> <tr bgcolor="#000000"><td colspan="2" width="100%"><img width=1 height=1 alt=""></td> </tr> </table> </body> </html>