312 lines
12 KiB
HTML
312 lines
12 KiB
HTML
<html>
|
|
<head>
|
|
<meta http-equiv="content-type" content="text/html; charset=UTF-8">
|
|
<title>Overview</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</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 class="screenshot">
|
|
<tr><td>
|
|
<a name="snap2"></a>
|
|
<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></tr>
|
|
<tr><td align="center">
|
|
<a href="howtos13.html#snap2">
|
|
<img src="images/good-cd.png">
|
|
</a>
|
|
</td></tr>
|
|
<tr><td align="center">Screen shot: Good CD</td></tr>
|
|
</table><pre> </pre>
|
|
<!--- 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>
|
|
<tr>
|
|
<td valign="top">
|
|
<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>
|
|
<td>
|
|
<a name="snap5"></a>
|
|
<table class="thumbnail" width="160px">
|
|
<tr><td><font size="-1">Defective CD</font></td></tr>
|
|
<tr><td><a href="howtos13_expand=5.html#snap5"><img src="thumbnails/defective-cd.png"></a></td></tr>
|
|
</table>
|
|
</td>
|
|
</tr>
|
|
</table><p>
|
|
<!--- 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>
|