82 lines
3.1 KiB
PHP
82 lines
3.1 KiB
PHP
<?php
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# dvdisaster: English homepage translation
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# Copyright (C) 2004-2010 Carsten Gnörlich
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#
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# UTF-8 trigger: äöüß
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#
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# Include our PHP sub routines, then call begin_page()
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# to start the HTML page, insert the header,
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# navigation and news if appropriate.
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require("../include/dvdisaster.php");
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require("../include/footnote.php");
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begin_page();
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howto_headline("Creating error correction files", "Archival", "images/create-icon.png");
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?>
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<!--- Insert actual page content below --->
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<h3>Tips for archival of error correction files</h3>
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CD/DVD/BD are currently among the most cost-effective exchangeable
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mass storage media. Therefore you are probably considering them
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for storing error correction files.<p>
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Nothing is wrong with doing so, but be aware that your data and protective
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error correction files are kept on media with equal reliability.
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When you encounter read errors on a data medium
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it is likely that the medium containing the respective error correction files
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has also gone defective. After all both media have been written at the same time,
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and they have the same aging characteristics.
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<p>
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<table width=100%><tr><td bgcolor=#000000 width=2><img width=1 height=1 alt=""></td>
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<td> </td>
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<td>This might come at a surprise, but it can not be guaranteed that an
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error correction file remains usable when it is stored on a defective medium.
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See the old documentation for an <a href="http://dvdisaster.net/legacy/en/background20.html">explanation of the technical background</a>.
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</td></tr></table><p>
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Therefore it is important to protect error correction files just as if
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they were normal data. To be more specific,
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the medium containing error correction files must be protected with
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error correction data as well. Here are two ways of doing this:
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<ol>
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<li>Storing error correction files on separate media:<p>
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Use additional media just for keeping the error correction files.
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If you use no more than 80% per medium for error correction files
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it can
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be <a href="howtos30.php">augmented with error correction data</a>.
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This allows you to recover the medium if you run into problems
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reading the error correction files at a later time.<p></li>
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<li>Storing error correction files on the next medium in sequence:<p>
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Maybe you are using media for an incremental backup strategy. In that
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case you could collect files until the first medium can be filled.
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Write that medium as usual and create an error correction file for it.
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Include that error correction file into the backup set which will go
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onto the second medium. When the second medium has been written, write
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the error correction file for it onto the third medium and so on.
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This way all media in the chain are protected with error correction
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files (with the ecc file for the last medium residing on hard disk until
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another medium is written).<p>
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Of course Murphys Law may strike and result in all media of the chain
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becoming defective. In that case you need to recover all media, starting
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with the most recent one ;-)
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</li>
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</ol>
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<!--- do not change below --->
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<?php
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# end_page() adds the footer line and closes the HTML properly.
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end_page();
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?>
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