152 lines
8.9 KiB
HTML
152 lines
8.9 KiB
HTML
<?xml version="1.0" encoding="UTF-8"?>
|
|
<!DOCTYPE html
|
|
PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
|
|
<html lang="en-us" xml:lang="en-us">
|
|
<head>
|
|
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
|
|
<meta name="security" content="public" />
|
|
<meta name="Robots" content="index,follow" />
|
|
<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))' />
|
|
<meta name="DC.Type" content="concept" />
|
|
<meta name="DC.Title" content="Device parity protection" />
|
|
<meta name="DC.Relation" scheme="URI" content="rzalydpconcepts.htm" />
|
|
<meta name="DC.Relation" scheme="URI" content="rzalydeviceparityben.htm" />
|
|
<meta name="DC.Relation" scheme="URI" content="rzalydeviceparitycost.htm" />
|
|
<meta name="DC.Relation" scheme="URI" content="rzalydppiop.htm" />
|
|
<meta name="DC.Relation" scheme="URI" content="rzalymigrating.htm" />
|
|
<meta name="DC.Relation" scheme="URI" content="rzalyelmdasdpp.htm" />
|
|
<meta name="DC.Relation" scheme="URI" content="rzalydppprf.htm" />
|
|
<meta name="DC.Relation" scheme="URI" content="rzalygeobenefits.htm" />
|
|
<meta name="DC.Relation" scheme="URI" content="rzalymirrorconcept.htm" />
|
|
<meta name="DC.Relation" scheme="URI" content="rzalypoolthreshold.htm" />
|
|
<meta name="DC.Relation" scheme="URI" content="rzalyexamplegeomirror.htm" />
|
|
<meta name="copyright" content="(C) Copyright IBM Corporation 2002, 2006" />
|
|
<meta name="DC.Rights.Owner" content="(C) Copyright IBM Corporation 2002, 2006" />
|
|
<meta name="DC.Format" content="XHTML" />
|
|
<meta name="DC.Identifier" content="hdrdpp" />
|
|
<meta name="DC.Language" content="en-us" />
|
|
<!-- All rights reserved. Licensed Materials Property of IBM -->
|
|
<!-- US Government Users Restricted Rights -->
|
|
<!-- Use, duplication or disclosure restricted by -->
|
|
<!-- GSA ADP Schedule Contract with IBM Corp. -->
|
|
<link rel="stylesheet" type="text/css" href="./ibmdita.css" />
|
|
<link rel="stylesheet" type="text/css" href="./ic.css" />
|
|
<title>Device parity protection</title>
|
|
</head>
|
|
<body id="hdrdpp"><a name="hdrdpp"><!-- --></a>
|
|
<!-- Java sync-link --><script language="Javascript" src="../rzahg/synch.js" type="text/javascript"></script>
|
|
<h1 class="topictitle1">Device parity protection</h1>
|
|
<div><p>Device parity protection is a hardware availability function that protects
|
|
data from being lost because of disk unit failure or because of damage to
|
|
a disk. To protect data, the disk input/output adapter (IOA) calculates and
|
|
saves a parity value for each bit of data. Conceptually, the IOA computes
|
|
the parity value from the data at the same location on each of the other disk
|
|
units in the device parity set. When a disk failure occurs, the data can be
|
|
reconstructed by using the parity value and the values of the bits in the
|
|
same locations on the other disks. The system continues to run while the data
|
|
is being reconstructed. The overall goal of device parity protection is to
|
|
provide high availability and to protect data as inexpensively as possible.</p>
|
|
<div class="section"><h4 class="sectiontitle">Two types of device parity protection</h4><p>RAID 5 and
|
|
RAID 6 are the two types of device parity protection. </p>
|
|
</div>
|
|
<div class="section"><h4 class="sectiontitle">RAID 5</h4><p>If more than one disk fails, you must restore
|
|
the data from the backup media. Logically, the capacity of one disk unit is
|
|
dedicated to storing parity data in a parity set. However, in practice the
|
|
parity data is spread among multiple disk units. Restoring data to a disk
|
|
pool that has disk units with device parity protection may take longer than
|
|
a disk pool that contains only unprotected disk units.</p>
|
|
<div class="p">Systems with
|
|
IOAs released after V5R2 can have a minimum number of 3 disk units in a parity
|
|
set. The maximum number of disk units in a parity set is 18.<div class="note"><span class="notetitle">Note:</span> Systems
|
|
with IOAs released before V5R2 of i5/OS™, the minimum number of disk units
|
|
in a parity set is 4. The maximum number of disk units in a parity set is
|
|
10.</div>
|
|
</div>
|
|
|
|
<div class="tablenoborder"><table cellpadding="4" cellspacing="0" summary="" width="100%" frame="border" border="1" rules="all"><thead align="left"><tr><th class="oddrowblue" align="left" valign="bottom" width="50%" id="d0e38">Number of disk
|
|
units in a parity set</th>
|
|
<th class="oddrowblue" align="left" valign="bottom" width="50%" id="d0e40">Number of disk
|
|
units that store parity</th>
|
|
</tr>
|
|
</thead>
|
|
<tbody><tr><td align="center" valign="top" width="50%" headers="d0e38 ">3</td>
|
|
<td align="center" valign="top" width="50%" headers="d0e40 ">2</td>
|
|
</tr>
|
|
<tr><td align="center" valign="top" width="50%" headers="d0e38 ">4-7</td>
|
|
<td align="center" valign="top" width="50%" headers="d0e40 ">4</td>
|
|
</tr>
|
|
<tr><td align="center" valign="top" width="50%" headers="d0e38 ">8-15</td>
|
|
<td align="center" valign="top" width="50%" headers="d0e40 ">8</td>
|
|
</tr>
|
|
<tr><td align="center" valign="top" width="50%" headers="d0e38 ">16-18</td>
|
|
<td align="center" valign="top" width="50%" headers="d0e40 ">16</td>
|
|
</tr>
|
|
</tbody>
|
|
</table>
|
|
</div>
|
|
</div>
|
|
<div class="section"><h4 class="sectiontitle">RAID 6</h4><p id="hdrdpp__raid6p1"><a name="hdrdpp__raid6p1"><!-- --></a>If more than two disk units
|
|
fail, you must restore the data from the backup media. Logically, the capacity
|
|
of two disk units is dedicated to storing parity data in a parity set. However,
|
|
in practice the parity data is spread among multiple disk units.</p>
|
|
<p>The
|
|
minimum number of disk units in a parity set is 4. The maximum number of disk
|
|
units in a parity set is 18. </p>
|
|
<p>When a RAID 6 parity set is started, all
|
|
of the disk units contain parity. Restoring data to a disk pool that has disk
|
|
units with device parity protection may take longer than a disk pool that
|
|
contains only unprotected disk units.</p>
|
|
<div class="note"><span class="notetitle">Note:</span> It is recommended that you
|
|
use more than four disk units in a RAID 6 device parity set, because the capacity
|
|
of two disk units is dedicated to storing parity data in a parity set.</div>
|
|
<p><img src="./delta.gif" alt="Start of change" />Raid 6 requires a new storage adapter that supports this new
|
|
function. The 571B is the first adapter to support Raid 6.<img src="./deltaend.gif" alt="End of change" /></p>
|
|
</div>
|
|
<div class="section"><h4 class="sectiontitle">Device parity protection is not a substitute for a backup
|
|
and recovery strategy</h4><p>Device parity protection is not a substitute
|
|
for a backup and recovery strategy. Device parity protection can prevent your
|
|
system from stopping when certain types of failures occur. It can speed up
|
|
your recovery process for certain types of failures. But device parity protection
|
|
does not protect you from many types of failures, such as a site disaster
|
|
or an operator or programmer error. It does not protect against system outages
|
|
that are caused by failures in other disk-related hardware (such as IOAs,
|
|
disk I/O processors, or a system bus).</p>
|
|
<p>If possible, you should protect
|
|
all the disk units on your system with either device parity protection or <a href="rzalymirror.htm">Work with mirrored protection</a>. This prevents the loss of information when
|
|
disk failure occurs. In many cases, you can also keep your system operational
|
|
while a disk unit is being repaired or replaced.</p>
|
|
<p>For information about
|
|
how to start using device parity protection, see <a href="../books/sc415304.pdf" target="_blank">Backup
|
|
and Recovery</a><img src="wbpdf.gif" alt="Link to PDF" />.</p>
|
|
</div>
|
|
</div>
|
|
<div>
|
|
<ul class="ullinks">
|
|
<li class="ulchildlink"><strong><a href="rzalydeviceparityben.htm">Benefits of device parity protection</a></strong><br />
|
|
</li>
|
|
<li class="ulchildlink"><strong><a href="rzalydeviceparitycost.htm">Costs and limitations of device parity protection</a></strong><br />
|
|
</li>
|
|
<li class="ulchildlink"><strong><a href="rzalydppiop.htm">How device parity protection works</a></strong><br />
|
|
</li>
|
|
<li class="ulchildlink"><strong><a href="rzalymigrating.htm">Migrating to a new input/output adapter</a></strong><br />
|
|
</li>
|
|
<li class="ulchildlink"><strong><a href="rzalyelmdasdpp.htm">Elements of device parity protection</a></strong><br />
|
|
</li>
|
|
<li class="ulchildlink"><strong><a href="rzalydppprf.htm">How device parity protection affects performance</a></strong><br />
|
|
</li>
|
|
</ul>
|
|
|
|
<div class="familylinks">
|
|
<div class="parentlink"><strong>Parent topic:</strong> <a href="rzalydpconcepts.htm">Disk protection</a></div>
|
|
</div>
|
|
<div class="relconcepts"><strong>Related concepts</strong><br />
|
|
<div><a href="rzalyexamplegeomirror.htm">Example: Independent disk pools with geographic mirroring</a></div>
|
|
</div>
|
|
<div class="relinfo"><strong>Related information</strong><br />
|
|
<div><a href="rzalygeobenefits.htm">Benefits of geographic mirroring</a></div>
|
|
<div><a href="rzalymirrorconcept.htm">Mirrored protection</a></div>
|
|
<div><a href="rzalypoolthreshold.htm">Set the threshold of a disk pool</a></div>
|
|
</div>
|
|
</div>
|
|
</body>
|
|
</html> |