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<html><head><meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"><title>Incremental Backups</title><link rel="stylesheet" type="text/css" href="styles.css"><meta name="generator" content="DocBook XSL Stylesheets V1.79.1"><link rel="home" href="index.html" title="Cedar Backup 3 Software Manual"><link rel="up" href="ch02.html" title="Chapter 2. Basic Concepts"><link rel="prev" href="ch02s07.html" title="Media and Device Types"><link rel="next" href="ch02s09.html" title="Extensions"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Incremental Backups</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="ch02s07.html">Prev</a> </td><th width="60%" align="center">Chapter 2. Basic Concepts</th><td width="20%" align="right"> <a accesskey="n" href="ch02s09.html">Next</a></td></tr></table><hr></div><div class="sect1"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="cedar-basic-incremental"></a>Incremental Backups</h2></div></div></div><p>
         Cedar Backup supports three different kinds of backups for individual
         collect directories.  These are <em class="firstterm">daily</em>,
         <em class="firstterm">weekly</em> and <em class="firstterm">incremental</em>
         backups.  Directories using the daily mode are backed up every day.
         Directories using the weekly mode are only backed up on the first day
         of the week, or when the <code class="option">--full</code> option is used.
         Directories using the incremental mode are always backed up on the
         first day of the week (like a weekly backup), but after that only the
         files which have changed are actually backed up on a daily basis.
      </p><p>
         In Cedar Backup, incremental backups are not based on date, but are
         instead based on saved checksums, one for each backed-up file.
         When a full backup is run, Cedar Backup gathers a checksum value
         <a href="#ftn.idm410" class="footnote" name="idm410"><sup class="footnote">[14]</sup></a> 
         for each backed-up file.  The next time an incremental backup is run,
         Cedar Backup checks its list of file/checksum pairs for each file that
         might be backed up.  If the file's checksum value does not
         match the saved value, or if the file does not appear in the list
         of file/checksum pairs, then it will be backed up and a new checksum
         value will be placed into the list.  Otherwise, the file will be
         ignored and the checksum value will be left unchanged.
      </p><p>
         Cedar Backup stores the file/checksum pairs in
         <code class="filename">.sha</code> files in its working directory, one file per
         configured collect directory.  The mappings in these files are reset
         at the start of the week or when the <code class="option">--full</code> option is
         used.  Because these files are used for an entire week, you should
         never purge the working directory more frequently than once per week.
      </p><div class="footnotes"><br><hr style="width:100; text-align:left;margin-left: 0"><div id="ftn.idm410" class="footnote"><p><a href="#idm410" class="para"><sup class="para">[14] </sup></a>The checksum is actually an <em class="firstterm">SHA
         cryptographic hash</em>.  See Wikipedia for more information:
         <a class="ulink" href="http://en.wikipedia.org/wiki/SHA-1" target="_top">http://en.wikipedia.org/wiki/SHA-1</a>.</p></div></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="ch02s07.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="ch02.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="ch02s09.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Media and Device Types </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> Extensions</td></tr></table></div></body></html>