138 lines
8.0 KiB
HTML
138 lines
8.0 KiB
HTML
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<!DOCTYPE html
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<meta name="DC.Title" content="Comparison of disk protection options" />
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<!-- All rights reserved. Licensed Materials Property of IBM -->
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<title>Comparison of disk protection options</title>
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</head>
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<body id="hdrcmpropts"><a name="hdrcmpropts"><!-- --></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">Comparison of disk protection options</h1>
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<div><p>You should be aware of these considerations when selecting disk protection
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options:</p>
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<p>When using RAID 5 device parity protection, the system continues
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to run after a single-disk failure. When using RAID 6 device parity protection,
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the system continues to run after a two-disk failure. With mirrored protection,
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the system might continue to run after the failure of a disk-related component,
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such as an IOA or an IOP. </p>
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<p>RAID 5 device parity protection requires the capacity of one
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disk unit that is dedicated to storing parity data in a parity set. RAID 6
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device parity protection requires the capacity of two disk units that are
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dedicated to storing parity data in a parity set. A system with mirrored protection
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requires twice as much disk capacity as the same system without mirrored protection
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because all information is stored twice. Mirrored protection might also require
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more buses, IOPs, and disk IOA, depending on the level of protection that
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you want. Therefore, mirrored protection is typically more expensive than
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device parity protection. </p>
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<p>Typically, neither device parity protection nor mirrored protection has
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a noticeable effect on system performance. In some cases, mirrored protection
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actually improves system performance. The time required to restore data to
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disk units that are protected by device parity protection is longer than the
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time required to restore to the same disk devices that do not have device
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parity protection activated. This is because the parity data must be calculated
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and written.</p>
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<div class="p">This table provides an overview of the availability tools that can be used
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on the server to protect against different types of failure.
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<div class="tablenoborder"><table cellpadding="4" cellspacing="0" summary="" width="100%" frame="border" border="1" rules="all"><thead align="left"><tr class="tablemainheaderbar"><th class="oddrowblue" align="left" valign="bottom" width="48%" id="d0e29">What type of
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availability is needed?</th>
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<th class="oddrowblue" align="left" valign="bottom" width="13%" id="d0e31">Device parity
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protection</th>
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<th class="oddrowblue" align="left" valign="bottom" width="13%" id="d0e33">Mirrored protection</th>
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<th class="oddrowblue" align="left" valign="bottom" width="13%" id="d0e35">Basic disk pools</th>
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<th class="oddrowblue" align="left" valign="bottom" width="13%" id="d0e37">Independent disk
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pool</th>
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</tr>
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</thead>
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<tbody><tr><td align="left" valign="top" width="48%" headers="d0e29 ">Protect from data loss due to disk-related
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hardware failure</td>
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<td align="left" valign="top" width="13%" headers="d0e31 ">Yes</td>
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<td align="left" valign="top" width="13%" headers="d0e33 ">Yes</td>
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<td align="left" valign="top" width="13%" headers="d0e35 ">See note 2</td>
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<td align="left" valign="top" width="13%" headers="d0e37 ">See note 2</td>
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</tr>
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<tr><td align="left" valign="top" width="48%" headers="d0e29 ">Maintain availability</td>
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<td align="left" valign="top" width="13%" headers="d0e31 ">Yes</td>
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<td align="left" valign="top" width="13%" headers="d0e33 ">Yes</td>
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<td align="left" valign="top" width="13%" headers="d0e35 ">No</td>
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<td align="left" valign="top" width="13%" headers="d0e37 ">Yes<sup>4</sup></td>
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</tr>
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<tr><td align="left" valign="top" width="48%" headers="d0e29 ">Help with disk unit recovery</td>
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<td align="left" valign="top" width="13%" headers="d0e31 ">Yes</td>
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<td align="left" valign="top" width="13%" headers="d0e33 ">Yes</td>
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<td align="left" valign="top" width="13%" headers="d0e35 ">Yes<sup>2</sup></td>
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<td align="left" valign="top" width="13%" headers="d0e37 ">Yes<sup>2</sup></td>
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</tr>
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<tr><td align="left" valign="top" width="48%" headers="d0e29 ">Maintain availability when input/output adapter
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(IOA) fails</td>
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<td align="left" valign="top" width="13%" headers="d0e31 ">No</td>
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<td align="left" valign="top" width="13%" headers="d0e33 ">Yes<sup>1</sup></td>
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<td align="left" valign="top" width="13%" headers="d0e35 ">No</td>
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<td align="left" valign="top" width="13%" headers="d0e37 ">No<sup>5</sup></td>
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</tr>
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<tr><td align="left" valign="top" width="48%" headers="d0e29 ">Maintain availability when disk I/O processor
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fails</td>
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<td align="left" valign="top" width="13%" headers="d0e31 ">No</td>
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<td align="left" valign="top" width="13%" headers="d0e33 ">Yes<sup>1</sup></td>
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<td align="left" valign="top" width="13%" headers="d0e35 ">No</td>
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<td align="left" valign="top" width="13%" headers="d0e37 ">No<sup>5</sup></td>
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</tr>
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<tr><td align="left" valign="top" width="48%" headers="d0e29 ">Maintain availability when system bus fails</td>
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<td align="left" valign="top" width="13%" headers="d0e31 ">No</td>
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<td align="left" valign="top" width="13%" headers="d0e33 ">Yes<sup>1</sup></td>
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<td align="left" valign="top" width="13%" headers="d0e35 ">No</td>
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<td align="left" valign="top" width="13%" headers="d0e37 ">No<sup>5</sup></td>
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</tr>
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<tr><td align="left" valign="top" width="48%" headers="d0e29 ">Site disaster protection</td>
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<td align="left" valign="top" width="13%" headers="d0e31 ">No</td>
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<td align="left" valign="top" width="13%" headers="d0e33 ">Yes<sup>3</sup></td>
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<td align="left" valign="top" width="13%" headers="d0e35 ">No</td>
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<td align="left" valign="top" width="13%" headers="d0e37 ">No<sup>5</sup></td>
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</tr>
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<tr><td align="left" valign="top" width="48%" headers="d0e29 ">Ability to switch data between systems</td>
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<td align="left" valign="top" width="13%" headers="d0e31 ">No</td>
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<td align="left" valign="top" width="13%" headers="d0e33 ">No</td>
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<td align="left" valign="top" width="13%" headers="d0e35 ">No</td>
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<td align="left" valign="top" width="13%" headers="d0e37 ">Yes</td>
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</tr>
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<tr><td colspan="5" align="left" valign="top" headers="d0e29 d0e31 d0e33 d0e35 d0e37 "> <p><span class="uicontrol">Notes:</span></p>
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<ol><li>Depends on hardware used, configuration, and level of mirrored protection.</li>
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<li>Configuring disk pools can limit the loss of data and the recovery to
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a single disk pool.</li>
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<li>For site disaster protection, remote mirroring is required.</li>
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<li>In a clustered environment, an independent disk pool can help maintain
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availability.</li>
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<li>When using geographic mirroring, independent disk pools can provide site
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disaster protection.</li>
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</ol>
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</td>
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</tr>
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</tbody>
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</table>
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</div>
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</div>
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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="rzalyprtctvsdtalss.htm">Plan for 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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