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HTML
129 lines
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<title>Switchable and stand-alone independent disk pools</title>
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</head>
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<body id="rzalyswitchablevsstandalone"><a name="rzalyswitchablevsstandalone"><!-- --></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">Switchable and stand-alone independent disk pools</h1>
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<div><p>There are two basic environments in which you can take advantage of independent
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disk pools: a multisystem environment managed by an iSeries™ cluster, and a single-system
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environment with a single iSeries server.</p>
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<div class="section"><h4 class="sectiontitle">Independent disk pools in a multisystem clustered environment</h4><div class="p"><img src="./delta.gif" alt="Start of change" />A group of servers in a cluster can take advantage of the switchover
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capability to move access to the independent disk pool from server to server.
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In this environment, an independent disk pool can be switchable when it resides
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on a switchable device. A switchable device can be an external expansion unit
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(tower), an input/output processor (IOP) on the bus shared by logical partitions,
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or an IOP or IOPless hardware that is assigned to an I/O pool. <div class="note"><span class="notetitle">Note:</span> Hardware
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that does not have a physical IOP has a virtual logical representation of
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the IOP.</div>
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A switchable device that contains an independent disk pool
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can be switched automatically in the case of an unplanned outage, or it can
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be switched manually by administering a switchover.<img src="./deltaend.gif" alt="End of change" /></div>
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<p>Another
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option that can be leveraged in a multisystem environment is <a href="rzalygeographicmirror.htm">geographic mirroring</a>. Geographic mirroring allows you
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to maintain two identical copies of an independent disk pool at two sites
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that are geographically separated. The independent disk pools at the separate
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sites can be switchable or dedicated.</p>
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</div>
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<div class="section"><h4 class="sectiontitle">Dedicated independent disk pools in a single-system environment</h4>An
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independent disk pool in a single-system environment, with no clustering
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and no switchable devices, is said to be a dedicated, private, or stand-alone
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independent disk pool. While you cannot switch the access to the independent
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disk pool amongst servers in this environment, you can still isolate data
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in an independent disk pool, keeping it separate from the rest of the disk
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storage on the server. The independent disk pool can then be made available
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(brought online) and made unavailable (taken offline) as needed. This might
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be done, for example, to isolate data associated with a specific application
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program or to isolate low-use data that is only needed periodically. Dedicated
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independent disk pools might also be used to consolidate data from several
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small servers at branch offices to one or more larger servers at a central
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location, while still keeping the data separate for each branch. <p>Independent
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disk pools allow you to isolate certain maintenance functions. Then, when
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you need to perform disk management functions that normally require the entire
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system to be at DST, you can perform them by merely varying off the affected
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independent disk pool.</p>
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<p>The following table compares dedicated independent
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disk pools and independent disk pools in a multisystem environment.</p>
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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" valign="bottom"><th class="oddrowblue" rowspan="2" valign="bottom" width="25.909528392685278%" id="d0e47">Consideration </th>
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<th class="oddrowblue" valign="bottom" width="26.564003849855634%" id="d0e49"> Dedicated</th>
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<th class="oddrowblue" colspan="2" align="center" valign="middle" id="d0e51"> Multisystem environment</th>
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</tr>
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<tr valign="bottom"><th class="oddrowblue" valign="bottom" width="26.564003849855634%" id="d0e54"> Single system</th>
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<th class="oddrowblue" valign="bottom" width="25.293551491819056%" id="d0e56">Multisystem cluster</th>
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<th class="oddrowblue" valign="bottom" width="22.23291626564004%" id="d0e58">Logical partitions in a cluster</th>
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</tr>
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</thead>
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<tbody><tr><td valign="top" width="25.909528392685278%" headers="d0e47 ">iSeries cluster
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required</td>
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<td valign="top" width="26.564003849855634%" headers="d0e49 d0e54 ">No</td>
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<td valign="top" width="25.293551491819056%" headers="d0e51 d0e56 ">Yes</td>
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<td valign="top" width="22.23291626564004%" headers="d0e51 d0e58 "> Yes</td>
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</tr>
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<tr><td valign="top" width="25.909528392685278%" headers="d0e47 ">Connectivity between systems</td>
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<td valign="top" width="26.564003849855634%" headers="d0e49 d0e54 ">Not applicable</td>
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<td valign="top" width="25.293551491819056%" headers="d0e51 d0e56 ">HSL loop</td>
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<td valign="top" width="22.23291626564004%" headers="d0e51 d0e58 ">Virtual OptiConnect</td>
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</tr>
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<tr><td valign="top" width="25.909528392685278%" headers="d0e47 ">Location of disk units</td>
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<td valign="top" width="26.564003849855634%" headers="d0e49 d0e54 ">Any supported internal or external disk units</td>
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<td valign="top" width="25.293551491819056%" headers="d0e51 d0e56 ">External expansion unit (tower)</td>
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<td valign="top" width="22.23291626564004%" headers="d0e51 d0e58 ">IOP on shared bus</td>
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</tr>
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<tr><td valign="top" width="25.909528392685278%" headers="d0e47 ">Switchability</td>
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<td valign="top" width="26.564003849855634%" headers="d0e49 d0e54 ">No</td>
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<td valign="top" width="25.293551491819056%" headers="d0e51 d0e56 ">Yes, between systems</td>
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<td valign="top" width="22.23291626564004%" headers="d0e51 d0e58 ">Yes, between partitions</td>
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</tr>
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<tr><td valign="top" width="25.909528392685278%" headers="d0e47 ">Switchable entity</td>
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<td valign="top" width="26.564003849855634%" headers="d0e49 d0e54 ">None</td>
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<td valign="top" width="25.293551491819056%" headers="d0e51 d0e56 "> Expansion unit</td>
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<td valign="top" width="22.23291626564004%" headers="d0e51 d0e58 "> IOP</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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<p>In a hardware switching environment, one node in the device domain
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owns it, and all the other nodes in the device domain show that the independent
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disk pool exists. In a geographic mirroring environment, one node at each
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site owns a copy of the independent disk pool. When an independent disk pool
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is created or deleted, the node creating or deleting the independent disk
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pool informs all the other nodes in the device domain of the change. If clustering
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is not active between the nodes, or a node is in the midst of a long running
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disk pool configuration change, that node will not update and will be inconsistent
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with the node rest of the nodes. Nodes must be consistent before a failover
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or switchover. Ending clustering and starting clustering will ensure that
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the configuration is consistent. </p>
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<p>For more on switchable and dedicated
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independent disk pools, including example configurations for each of these
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environments, see <a href="rzalyscenarios.htm">Examples: Independent disk pool configurations</a>.</p>
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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="rzalyconcepts.htm">Independent disk pools</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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