62 lines
3.7 KiB
HTML
62 lines
3.7 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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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
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<meta name="security" content="public" />
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<meta http-equiv="PICS-Label" content='(PICS-1.1 "http://www.icra.org/ratingsv02.html" l gen true r (cz 1 lz 1 nz 1 oz 1 vz 1) "http://www.rsac.org/ratingsv01.html" l gen true r (n 0 s 0 v 0 l 0) "http://www.classify.org/safesurf/" l gen true r (SS~~000 1))' />
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<meta name="DC.Type" content="topic" />
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<meta name="DC.Title" content="Mirrored protection and performance" />
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<meta name="DC.Relation" scheme="URI" content="rzalydpconcepts.htm" />
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<meta name="copyright" content="(C) Copyright IBM Corporation 2002, 2006" />
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<meta name="DC.Rights.Owner" content="(C) Copyright IBM Corporation 2002, 2006" />
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<meta name="DC.Format" content="XHTML" />
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<meta name="DC.Identifier" content="hdrmirrorperf" />
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<meta name="DC.Language" content="en-us" />
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<!-- All rights reserved. Licensed Materials Property of IBM -->
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<!-- US Government Users Restricted Rights -->
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<!-- Use, duplication or disclosure restricted by -->
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<!-- GSA ADP Schedule Contract with IBM Corp. -->
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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>Mirrored protection and performance</title>
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</head>
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<body id="hdrmirrorperf"><a name="hdrmirrorperf"><!-- --></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">Mirrored protection and performance</h1>
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<div><p>When mirrored protection is started, most systems show little difference
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in performance; in some cases, mirrored protection can improve performance.
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Generally, functions that do mostly read operations see equal or better performance
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with mirrored protection. This is because read operations have a choice of
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two storage units to read from, and the one with the faster expected response
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time is selected. Operations that do mostly write operations (such as updating
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database records) might see slightly reduced performance on a system that
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has mirrored protection because all changes must be written to both storage
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units of the mirrored pair. Thus, restore operations are slower.</p>
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<p>In some cases, if the system ends abnormally, the system cannot determine
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whether the last updates were written to both storage units of each mirrored
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pair. If the system cannot determine whether the last changes were written
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to both storage units of the mirrored pair, the system synchronizes the mirrored
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pair by copying the data in question from one storage unit of each mirrored
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pair to the other storage unit. The synchronization occurs during the IPL
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that follows the abnormal system end. If the system can save a copy of main
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storage before it ends, the synchronization process takes just a few minutes.
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If not, the synchronization process can take much longer. The extreme case
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might be close to a complete synchronization.</p>
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<p>If you have frequent power outages, you might want to consider adding an
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uninterruptible power supply to your system. Should main power be lost, the
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uninterruptible power supply allows the system to continue. A basic uninterruptible
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power supply allows the system time to save a copy of main storage before
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ending, which avoids long recovery. Both storage units of the load source
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mirrored pair must be powered by the basic uninterruptible power supply.</p>
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<p></p>
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</div>
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<div>
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<div class="familylinks">
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<div class="parentlink"><strong>Parent topic:</strong> <a href="rzalydpconcepts.htm">Disk 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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