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documentation/en/howtos24.php

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+<?php
+# dvdisaster: English homepage translation
+# Copyright (C) 2004-2009 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/footnote.php");
+begin_page();
+
+howto_headline("Creating error correction files", "Archival", "images/create-icon.png");
+?>
+
+<!--- Insert actual page content below --->
+<h3>Tips for archival of error correction files</h3>
+
+CD/DVD/BD are currently among the most cost-effective exchangeable
+mass storage media. Therefore you are probably considering them 
+for storing error correction files.<p>
+
+Nothing is wrong with doing so, but be aware that your data and protective
+error correction files are kept on media with equal reliability.
+When you encounter read errors on a data medium 
+it is likely that the medium containing the respective error correction files
+has also gone defective. After all both media have been written at the same time,
+and they have the same aging characteristics.
+<p>
+
+<table width=100%><tr><td bgcolor=#000000 width=2><img width=1 height=1 alt=""></td>
+<td>&nbsp;</td>
+<td>This might come at a surprise, but it can not be guaranteed that an
+error correction file remains usable when it is stored on a defective medium.
+See the old documentation for an <a href="http://dvdisaster.net/legacy/en/background20.html">explanation of the technical background</a>.
+</td></tr></table><p>
+
+Therefore it is important to protect error correction files just as if 
+they were normal data. To be more specific,  
+the medium containing error correction files must be protected with
+error correction data as well. Here are two ways of doing this:
+
+
+<ol>
+<li>Storing error correction files on separate media:<p>
+
+Use additional media just for keeping the error correction files.
+If you use no more than 80% per medium for error correction files
+it can 
+be <a href="howtos30.php">augmented with error correction data</a>. 
+This allows you to recover the medium if you run into problems
+reading the error correction files at a later time.<p></li>
+
+<li>Storing error correction files on the next medium in sequence:<p>
+
+Maybe you are using media for an incremental backup strategy. In that 
+case you could collect files until the first medium can be filled.
+Write that medium as usual and create an error correction file for it.
+Include that error correction file into the backup set which will go
+onto the second medium. When the second medium has been written, write
+the error correction file for it onto the third medium and so on. 
+This way all media in the chain are protected with error correction 
+files (with the ecc file for the last medium residing on hard disk until
+another medium is written).<p>
+
+Of course Murphys Law may strike and result in all media of the chain
+becoming defective. In that case you need to recover all media, starting
+with the most recent one ;-)
+</li>
+</ol>
+
+<!--- do not change below --->
+
+<?php
+
+# end_page() adds the footer line and closes the HTML properly.
+
+end_page();
+?>