116 lines
4.0 KiB
PHP
116 lines
4.0 KiB
PHP
<?php
|
|
# dvdisaster: English homepage translation
|
|
# Copyright (C) 2004-2012 Carsten Gnörlich
|
|
#
|
|
# UTF-8 trigger: äöüß
|
|
#
|
|
# Include our PHP sub routines, then call begin_page()
|
|
# to start the HTML page, insert the header,
|
|
# navigation and news if appropriate.
|
|
|
|
require("../include/dvdisaster.php");
|
|
require("../include/screenshot.php");
|
|
|
|
begin_page();
|
|
?>
|
|
|
|
<!-- Insert actual page content below -->
|
|
|
|
<h3 class="top">The adaptive reading strategy</h3>
|
|
|
|
dvdisaster contains two different reading strategies.<p>
|
|
|
|
<b>The adaptive reading strategy is recommended for:</b><p>
|
|
<ul>
|
|
<li><a href="howtos42.php">extracting data</a> from damaged media
|
|
</li>
|
|
</ul>
|
|
|
|
<b>The <a href="qa34.php">linear reading strategy</a> is recommended for:</b><p>
|
|
<ul>
|
|
<li><a href="howtos23.php">creating images</a> from undamaged media, e.g. to generate the error correction file</li>
|
|
<li><a href="howtos12.php">scanning the medium</a> for reading speed and read errors</li>
|
|
</ul>
|
|
|
|
<pre> </pre>
|
|
|
|
<b>Properties of the adaptive reading strategy.</b><p>
|
|
|
|
The adaptive reading strategy uses a "divide and conquer" approach for locating
|
|
still readable portions of a damaged medium. The strategy is based upon an article
|
|
published by Harald Bögeholz in c't-Magazin 16/2005 where it was published together
|
|
with the program <i>h2cdimage</i>:
|
|
|
|
<ol>
|
|
<li>
|
|
At the beginning the medium is considered as a single unread interval. Reading begins
|
|
with sector zero.<p>
|
|
</li>
|
|
<li>
|
|
The reading process continues sequentially unless either the end of the current interval
|
|
or a read error is encountered.<p>
|
|
</li>
|
|
<li>
|
|
The reading process is terminated if either (3a) sufficient sectors for a successful
|
|
error correction have been read or (3b) no unreadable intervals exceeding a given size
|
|
remain.
|
|
<p>
|
|
</li>
|
|
<li>
|
|
Otherwise the largest remaining unread interval will be determined. Reading continues in the middle
|
|
(e.g. second half) of this interval;
|
|
the first half of this interval is kept for a later reading pass.
|
|
</li>
|
|
</ol>
|
|
|
|
<?php begin_screen_shot("Adaptive reading in progress","adaptive-progress.png"); ?>
|
|
The termination criterium (3a) is especially efficient: Reading will stop as soon
|
|
as enough sectors have been collected for a successful image recovery using the
|
|
error correction file. This can reduce the reading time by as much as 90 percent
|
|
compared with a full read attempt, but does of course only work when
|
|
an error correction file is available.<p>
|
|
<?php end_screen_shot(); ?><p>
|
|
|
|
<pre> </pre>
|
|
|
|
<a name="configure"></a>
|
|
<b>Configuration</b><p>
|
|
|
|
<b>Error correction file.</b>
|
|
Adaptive reading works best when error correction data is available.
|
|
Obviously the error correction data must have been
|
|
<a href="howtos21.php">created</a>
|
|
at a time where the medium was still fully readable. To use a error correction file
|
|
during adaptive reading,
|
|
<a href="howtos42.php#select_eccfile">enter its name</a> before starting the reading process.<p>
|
|
|
|
<b>Limiting the adaptive reading range.</b> Reading can be
|
|
<a href="howtos11.php#image">limited</a> to a part of the medium.
|
|
|
|
This is not recommended when error correction data is used since the limit
|
|
might prevent sectors from being read which are required
|
|
for a succesful error correction.
|
|
If no error correction data is available,
|
|
limiting the reading range might be helpful
|
|
during multiple reading attempts.<p>
|
|
|
|
<b>Early reading termination.</b>
|
|
If no error correction data is available, adaptive reading will stop when no unread
|
|
intervals
|
|
<a href="howtos41.php#reading_attempts">larger than a selectable size</a> remain.<p>
|
|
|
|
The termination value should not be smaller than 128.
|
|
Otherwise the laser head will have to carry out lots of repositioning moves during the
|
|
final phase of the reading process. This will negatively affect both the life expectancy
|
|
of the drive and its reading capability. A better approach is to stop adaptive
|
|
reading earlier and then try reading the remaining sectors with an additional
|
|
<a href="qa34.php">linear reading</a> pass.
|
|
|
|
<!-- do not change below -->
|
|
|
|
<?php
|
|
# end_page() adds the footer line and closes the HTML properly.
|
|
|
|
end_page();
|
|
?>
|