146 lines
9.1 KiB
HTML
146 lines
9.1 KiB
HTML
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<meta name="DC.Title" content="Failover and switchover" />
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<title>Failover and switchover</title>
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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">Failover and switchover</h1>
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<div><div class="section"><h4 class="sectiontitle">Mirror copy failover or switchover</h4><p>A failover or
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switchover of the mirror copy when the independent disk pool is online results
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in a synchronization.</p>
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<p>A failover or switchover of the mirror copy to
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another node at that site when the independent disk pool is online results
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in a synchronization.</p>
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</div>
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<div class="section"><h4 class="sectiontitle">When geographic mirroring is suspended</h4><p>While geographic
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mirroring is suspended, a switchover or failover to the mirror copy is prohibited
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because the mirror copy contains back-level data. However, in the case where
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the production copy is lost, you can change the order of the recovery domain
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nodes to convert such a back-level mirror copy into the production copy. Do
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this by changing the backup node which owns the mirror copy into a primary
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node. If geographic mirroring is suspended for some of the independent disk
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pools in the disk pool group, but not all of the independent disk pools in
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the disk pool group, you cannot convert the mirror copy into a production
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copy even by changing the order of the recovery domain nodes. If geographic
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mirroring is suspended for all of the independent disk pools in the group,
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you can change the order of the recovery domain names. If the independent
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disk pools were suspended at different times, then the mirror copies are inconsistent
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and you should not try to convert these inconsistent mirror copies into the
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production copy. </p>
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</div>
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<div class="section"><h4 class="sectiontitle">Examples</h4><p>The following are examples of failovers
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and switchovers:</p>
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<ul><li>If the backup node is at the same site as the current primary node, then
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a failover or switchover of the primary node causes the production copy to
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switch hardware to that backup node. The former backup node at the same site
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becomes the primary node. The new primary node performs geographic mirroring
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to a node at the mirror copy site. </li>
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<li>If the backup node is at the other site, then a failover or switchover
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of the primary node causes the production copy to swap roles with the mirror
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copy on the backup node. The former backup node at the other site becomes
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the primary node. One of the remaining nodes in the recovery domain becomes
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the backup node at the new mirror copy site.</li>
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<li>If the backup node that owns the mirror copy undergoes a failover or switchover,
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then the mirror copy moves to the next backup node. </li>
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<li>If the backup node that owns the mirror copy undergoes a failover or switchover
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and no other backup node is defined, then geographic mirroring is suspended.</li>
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</ul>
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<div class="note"><span class="notetitle">Note:</span> A full or partial synchronization is required once geographic
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mirroring resumes after being in a suspended state.</div>
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</div>
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<div class="section"><h4 class="sectiontitle">Ending clustering</h4><div class="p">Do not end clustering on a node
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that is performing geographic mirroring. Such nodes own either a production
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copy or a mirror copy. The following results occur when ending clustering
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while performing geographic mirroring: <ul><li>Ending clustering for the node that owns the production copy when the
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cluster resource group is active causes failover. </li>
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<li>Ending clustering for the node that owns the mirror copy when the cluster
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resource group is active causes failover of the mirror copy.</li>
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<li>Ending clustering for the node that owns the mirror copy when failover
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cannot occur, because the cluster resource group is inactive or because there
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is no other active node at the mirror copy site, prevents recovery from TCP/IP
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connection failures.</li>
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</ul>
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</div>
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<p>If you ended clustering inadvertently, you should restart clustering,
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make the independent disk pools in the cluster resource group unavailable
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at your first opportunity, then make the Independent ASPs available again.
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When clustering is ended, geographic mirroring cannot recover from certain
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communications failures until both clustering and geographic mirroring are
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restarted. </p>
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</div>
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<div class="section"><h4 class="sectiontitle">Shut down system</h4><div class="p">If the system owning the mirror
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copy must be shutdown while performing geographic mirroring, you should do
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one of the following to avoid causing the application on the production copy
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to wait for the recovery timeout: <ul><li>If another active node is at the mirror copy site, switch the mirror copy
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to the other node. As part of the switchover, geographic mirroring is suspended,
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but without the timeout delay.</li>
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<li>If no other active node is at the mirror copy site, suspend geographic
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mirroring before shutting down the mirror copy system which avoids the recovery
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timeout delay. Synchronization is required once geographic mirroring is suspended.</li>
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</ul>
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<div class="note"><span class="notetitle">Note:</span> <img src="./delta.gif" alt="Start of change" />After suspending geographic mirroring, a full resynchronization
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is required when tracking is used or a partial synchronization is required
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when tracking in not used. Synchronization is required once geographic mirroring
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is resumed. <img src="./deltaend.gif" alt="End of change" /></div>
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</div>
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<p>Do not shut down the TCP system on
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a node that is performing geographic mirroring. Such nodes own either a production
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copy or a mirror copy. The following results occur if the TCP system is shut
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down:</p>
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<ul><li>If TCP is shutdown on production copy node and cluster resource group
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is active, failover occurs to the mirror copy.</li>
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<li>If TCP Is shutdown on mirror copy node, geographic mirroring is suspended.</li>
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</ul>
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</div>
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<div class="section"><h4 class="sectiontitle">Recovery from two production copies</h4><p>For successive failovers when performing geographic mirroring,
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the situation can arise that you have two production copies. Ordinarily, the
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production copy and the mirror copy remain consistent, so the next make available
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or resume automatically changes the former production copy to become the mirror
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copy, and the next make available will synchronize the new mirror copy. However,
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when the two nodes were not communicating, the users may have made both production
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copies available independently by suspending geographic mirroring. In this
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case, the system does not know which production copy the user wants. You must
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resolve the inconsistency by changing the recovery domain order. Once the
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node to serve as the production copy has been selected, the other production
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copy node becomes a mirror copy and is synchronized to the production copy.</p>
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</div>
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<div class="section"><h4 class="sectiontitle">Considerations for making a disk pool available at failover
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or switchover</h4><p>When you specify *ONLINE for the Configuration object
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online, the system automates the vary-on as part of failover or switchover;
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therefore, you do not have to issue the vary-on. However, if a geographic
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mirroring problem occurs during the vary-on, the system suspends geographic
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mirroring and completes the vary-on. You might prefer to fix the problem and
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keep geographic mirroring active. Also, if the vary-on fails, the system
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attempts to go back to the original primary node and vary-on the independent
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ASP back to the original primary node. You might prefer to fix the problem
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and vary-on the independent ASP to the new primary node. </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="rzalygeographicmirror.htm">Geographic mirroring</a></div>
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</div>
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</div>
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</body>
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