75 lines
4.2 KiB
HTML
75 lines
4.2 KiB
HTML
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<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE html
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PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html lang="en-us" xml:lang="en-us">
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<meta name="DC.Title" content="How device parity protection affects performance" />
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<meta name="DC.Relation" scheme="URI" content="rzalydpp.htm" />
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<meta name="copyright" content="(C) Copyright IBM Corporation 2002, 2006" />
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<!-- All rights reserved. Licensed Materials Property of IBM -->
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<link rel="stylesheet" type="text/css" href="./ibmdita.css" />
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<link rel="stylesheet" type="text/css" href="./ic.css" />
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<title>How device parity protection affects performance </title>
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</head>
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<body id="hdrdppprf"><a name="hdrdppprf"><!-- --></a>
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<!-- Java sync-link --><script language="Javascript" src="../rzahg/synch.js" type="text/javascript"></script>
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<h1 class="topictitle1">How device parity protection affects performance </h1>
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<div><div class="section"><h4 class="sectiontitle">RAID 5</h4><p>Device parity protection requires extra I/O
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operations to save the parity data. To avoid performance problems, all IOAs
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contain a nonvolatile write cache that ensures data integrity and provides
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faster write capability. The system is notified that a write operation is
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complete as soon as a copy of the data is stored in the write cache. Data
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is collected in the cache before it gets written to a disk unit. This collection
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technique reduces the number of physical write operations to the disk unit.
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Because of the cache, performance is generally about the same on protected
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and unprotected disk units.</p>
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<p>Applications that have many write requests
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in a short period of time, such as batch programs, can adversely affect performance.
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Disk unit failures can adversely affect the performance for both read and
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write operations.</p>
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<p>The additional processing that is associated with
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a disk unit failure in a device parity set can be significant. The decrease
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in performance is in effect until both the failed unit is repaired (or replaced)
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and the rebuild process is complete. If device parity protection decreases
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performance too much, consider using mirrored protection. </p>
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</div>
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<div class="section"><h4 class="sectiontitle">RAID 6</h4><p>Because there is
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a capacity of two disk units dedicated to storing parity data in a parity
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set for RAID 6, more I/O operations occur with RAID 6 than RAID 5. This may
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cause the performance to decrease.</p>
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</div>
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</div>
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<div>
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<ul class="ullinks">
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<li class="ulchildlink"><strong><a href="rzalyrdopsfail.htm">Read operations on a failed disk unit</a></strong><br />
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</li>
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<li class="ulchildlink"><strong><a href="rzalywrtopsfail.htm">Write operations on a failed disk unit</a></strong><br />
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</li>
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<li class="ulchildlink"><strong><a href="rzalyopsrbldproc.htm">Input/output operations during a rebuild process</a></strong><br />
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</li>
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<li class="ulchildlink"><strong><a href="rzalyauxiliary.htm">Write cache and auxiliary write cache IOA</a></strong><br />
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</li>
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</ul>
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<div class="familylinks">
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<div class="parentlink"><strong>Parent topic:</strong> <a href="rzalydpp.htm">Device parity protection</a></div>
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</div>
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</div>
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</body>
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</html>
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