55 lines
2.3 KiB
HTML
55 lines
2.3 KiB
HTML
<html>
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
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<link rel="stylesheet" href="style.css">
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<title>Introducing Parchive</title>
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</head>
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<body>
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<font size=5>Introduction to Parchive</font>
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<hr>
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<p> 
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PAR is a clipped from Parchive or Parity Archive, which means container of parity.
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Even if original files are damaged or lost,
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it is possible to repair them by extracting the parity.
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Two types of PAR files are made in same time.
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While an index file contains data for verification only,
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recovery files contain data for both verification and repair.
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Normally they don't distinguish, and they are just called as PAR files.
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</p>
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<p>
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<table>
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<tr><td>Example of PAR1 files:</td></tr>
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<tr><td><tt>Data.PAR</tt></td><td>Index file</td></tr>
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<tr><td><tt>Data.P01</tt></td><td>First recovery file</td></tr>
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<tr><td><tt>Data.P02</tt></td><td>Second recovery file</td></tr>
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<tr><td><tt>Data.P03</tt></td><td>Third recovery file</td></tr>
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<tr><td><font size=1> </font></td></tr>
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<tr><td>Example of PAR2 files:</td></tr>
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<tr><td><tt>Data.PAR2</tt></td><td>Index file</td></tr>
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<tr><td><tt>Data.vol0+1.PAR2</tt></td><td>First recovery file, which contains 1 recovery block</td></tr>
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<tr><td><tt>Data.vol1+2.PAR2</tt></td><td>Second recovery file, which contains 2 recovery blocks</td></tr>
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<tr><td><tt>Data.vol3+4.PAR2</tt></td><td>Third recovery file, which contains 4 recovery blocks</td></tr>
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</table>
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</p>
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<p> 
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Though the index file is usable for verification only,
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it is very smaller than recovery files.
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The construction of recovery file is different between PAR1 and PAR2.
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In PAR1, recovery data is calculated for a group of arrayed source files.
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The requirement is simple like;
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it requires 1 recovery file to restore 1 file, or it requires 3 recovery files to restore 3 files.
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</p>
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<p> 
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In PAR2, recovery data is calculated for a group of allocated blocks in all source files.
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While saving the recovery data,
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it is possible to change the number of recovery blocks in each recovery file.
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Thus, the required number of recovery files can be minimum by their required recovery blocks.
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In above example, you need second recovery file to recover 2 blocks,
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or you need first and third recovery files to recover 5 blocks.
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</p>
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</body>
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</html>
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