192 lines
13 KiB
HTML
192 lines
13 KiB
HTML
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<meta name="DC.Type" content="concept" />
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<meta name="DC.Title" content="Recovery domain" />
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<meta name="abstract" content="A recovery domain is a subset of cluster nodes that are grouped together in a cluster resource group (CRG) for a common purpose such as performing a recovery action or synchronizing events." />
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<meta name="description" content="A recovery domain is a subset of cluster nodes that are grouped together in a cluster resource group (CRG) for a common purpose such as performing a recovery action or synchronizing events." />
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<!-- All rights reserved. Licensed Materials Property of IBM -->
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<link rel="stylesheet" type="text/css" href="./ic.css" />
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<title>Recovery domain</title>
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</head>
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<body id="rzaigconceptsrecoverydomain"><a name="rzaigconceptsrecoverydomain"><!-- --></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">Recovery domain</h1>
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<div><p><span><img src="./delta.gif" alt="Start of change" />A <dfn class="term">recovery domain</dfn> is a subset of
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cluster nodes that are grouped together in a cluster resource group (CRG)
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for a common purpose such as performing a recovery action or synchronizing
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events.<img src="./deltaend.gif" alt="End of change" /></span></p>
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<p> A domain represents those nodes of the cluster from which cluster resource
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can be accessed. This subset of cluster nodes that is assigned to a particular
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cluster resource group either supports the primary point of access, secondary
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(backup) point of access, replicate point of access, or peer point of access.</p>
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<p>The four types of roles a node can have in a recovery domain are:</p>
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<dl><dt class="dlterm">Primary</dt>
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<dd>The cluster node that is the primary point of access for the resilient
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cluster resource. <ul><li>For a data CRG, the primary node contains the principle copy of a resource.</li>
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<li>For an application CRG, the primary node is the system on which the application
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is currently running.</li>
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<li>For a device CRG, the primary node is the current owner of the device
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resource.<div class="note"><span class="notetitle">Note:</span> <img src="./delta.gif" alt="Start of change" />When using geographic mirroring, the nodes in
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the recovery domain of a device CRG require a site name and data port IP addresses.
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See <a href="../apis/clust3a1TOC.htm">Site name
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and data port IP addresses</a> for details.<img src="./deltaend.gif" alt="End of change" /></div>
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</li>
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<li><img src="./delta.gif" alt="Start of change" />For a peer CRG, the primary node is not supported.<img src="./deltaend.gif" alt="End of change" /></li>
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</ul>
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<p><img src="./delta.gif" alt="Start of change" />If the primary node for a CRG fails, or a manual switchover
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is initiated, then the primary point of access for that CRG is moved to the
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first backup node<img src="./deltaend.gif" alt="End of change" /></p>
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</dd>
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<dt class="dlterm">Backup</dt>
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<dd>The cluster node that will take over the role of primary access if the
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present primary node fails or a manual switchover is initiated. <ul><li><img src="./delta.gif" alt="Start of change" />For a data CRG, this cluster node contains a copy of that
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resource which is kept current with replication.<img src="./deltaend.gif" alt="End of change" /></li>
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<li><img src="./delta.gif" alt="Start of change" />For a peer CRG, the backup node is not supported.<img src="./deltaend.gif" alt="End of change" /></li>
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</ul>
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</dd>
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<dt class="dlterm">Replicate</dt>
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<dd><img src="./delta.gif" alt="Start of change" />A cluster node that has copies of cluster resources, but
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is unable to assume the role of primary or backup. Failover or switchover
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to a replicate node is not allowed. If you ever want a replicate node to become
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a primary, you must first change the role of the replicate node to that of
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a backup node. <ul><li>For peer CRGs, nodes defined as replicate represent the inactive access
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point for cluster resources.</li>
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</ul>
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<img src="./deltaend.gif" alt="End of change" /></dd>
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<dt class="dlterm"><img src="./delta.gif" alt="Start of change" />Peer<img src="./deltaend.gif" alt="End of change" /></dt>
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<dd><img src="./delta.gif" alt="Start of change" />A cluster node which is not ordered and can be an active
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access point for cluster resources. When the CRG is started, all the nodes
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defined as peer will be an active access point. <ul><li>For a peer CRG, the access point is controlled entirely by the management
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application and not the system. The peer role is only supported by the peer
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CRG.</li>
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</ul>
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<img src="./deltaend.gif" alt="End of change" /></dd>
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</dl>
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<div class="section"><h4 class="sectiontitle">Primary-backup model</h4><p>For nodes that participate
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in a primary-backup model, each node in the recovery domain has a role with
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respect to the current operational environment of the cluster. This is called
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its <dfn class="term">current role</dfn> in the recovery domain. As the cluster goes
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through operational changes such as nodes ending, nodes starting, and nodes
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failing, the node's current role is changed accordingly. Each node in the
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recovery domain also has a role with respect to the preferred or ideal cluster
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environment. This is called its <dfn class="term"> preferred role</dfn> in
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the recovery domain. The preferred role is a static definition that is initially
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set when the cluster resource group is created. As the cluster environment
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changes, this role is not changed. The preferred role is only changed when
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nodes are added or removed from the recovery domain, or when a node is removed
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from the cluster. You can also manually change the preferred roles. </p>
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<p>Conceptually,
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you can view the recovery domain within a primary-backup model as follows:</p>
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<div class="tablenoborder"><table cellpadding="4" cellspacing="0" summary="" frame="border" border="1" rules="all"><caption>Table 1. Node roles for primary-backup CRGs</caption><thead align="left"><tr><th valign="top" id="d0e117">Node</th>
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<th valign="top" id="d0e119">Current role</th>
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<th valign="top" id="d0e121">Preferred role</th>
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</tr>
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</thead>
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<tbody><tr><td valign="top" headers="d0e117 ">A</td>
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<td valign="top" headers="d0e119 ">Backup 1</td>
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<td valign="top" headers="d0e121 ">Primary</td>
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</tr>
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<tr><td valign="top" headers="d0e117 ">B</td>
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<td valign="top" headers="d0e119 ">Backup 2</td>
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<td valign="top" headers="d0e121 ">Backup 1</td>
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</tr>
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<tr><td valign="top" headers="d0e117 ">C</td>
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<td valign="top" headers="d0e119 ">Primary</td>
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<td valign="top" headers="d0e121 ">Backup 2</td>
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</tr>
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<tr><td valign="top" headers="d0e117 ">D</td>
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<td valign="top" headers="d0e119 ">Replicate</td>
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<td valign="top" headers="d0e121 ">Replicate</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><img src="./delta.gif" alt="Start of change" />In this example, Nodes A, B, C, and D provide an
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example of a CRG that is a primary-backup model. Node C is serving as the
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current primary node. Because it has a preferred role of the second backup,
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Node C's current role as primary results from two failover or switchover actions.
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Upon the first failover or switchover action, the primary role moved from
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Node A to Node B since Node B is defined as the first backup. The second failover
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or switchover triggered Node C to become the primary node since it is defined
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as the second backup node. Node D current and preferred role is that of replicate.
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A replicate node cannot be the assume the point of access during a failover
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or switchover unless its role is changed manually to either primary or backup.<img src="./deltaend.gif" alt="End of change" /></p>
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<div class="note"><span class="notetitle">Note:</span> The
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role of each node in the recovery domain can also be changed manually. The
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example illustrates how the roles in the recovery domain change when switchover
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or failover actions occur and no manual changes are made to the designation
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of the roles in the recovery domain.</div>
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</div>
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<div class="section"><h4 class="sectiontitle">Peer model</h4><p><img src="./delta.gif" alt="Start of change" />For peer model, a node
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within a cluster resource groups can have one of two roles: peer or replicate. <img src="./deltaend.gif" alt="End of change" /></p>
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<div class="tablenoborder"><img src="./delta.gif" alt="Start of change" /><table cellpadding="4" cellspacing="0" summary="" frame="border" border="1" rules="all"><caption>Table 2. Node roles for peer CRGs</caption><thead align="left"><tr><th valign="top" width="33.33333333333333%" id="d0e170">Node</th>
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<th valign="top" width="33.33333333333333%" id="d0e172">Current role</th>
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<th valign="top" width="33.33333333333333%" id="d0e174">Preferred role</th>
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</tr>
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</thead>
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<tbody><tr><td valign="top" width="33.33333333333333%" headers="d0e170 ">A</td>
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<td valign="top" width="33.33333333333333%" headers="d0e172 ">Peer</td>
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<td valign="top" width="33.33333333333333%" headers="d0e174 ">Peer</td>
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</tr>
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<tr><td valign="top" width="33.33333333333333%" headers="d0e170 ">B</td>
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<td valign="top" width="33.33333333333333%" headers="d0e172 ">Peer</td>
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<td valign="top" width="33.33333333333333%" headers="d0e174 ">Peer</td>
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</tr>
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<tr><td valign="top" width="33.33333333333333%" headers="d0e170 ">C</td>
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<td valign="top" width="33.33333333333333%" headers="d0e172 ">Peer</td>
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<td valign="top" width="33.33333333333333%" headers="d0e174 ">Peer</td>
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</tr>
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<tr><td valign="top" width="33.33333333333333%" headers="d0e170 ">D</td>
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<td valign="top" width="33.33333333333333%" headers="d0e172 ">Replicate</td>
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<td valign="top" width="33.33333333333333%" headers="d0e174 ">Replicate</td>
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</tr>
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</tbody>
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</table>
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<img src="./deltaend.gif" alt="End of change" /></div>
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<p><img src="./delta.gif" alt="Start of change" /> Nodes A, B, and C are defined in the recovery domain
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as peer nodes. When a failure occurs on Node A, it is communicated to all
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nodes in recovery domain regardless of current role. These nodes resumes the
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operation at the point when Node A failed. Node D contains the data, but cannot
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resume the operation since it is defined as Replicate.<img src="./deltaend.gif" alt="End of change" /></p>
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<p>Any number of
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nodes can be designated as the peer or replicate. Peer nodes are not ordered
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and can become an active access point for the cluster resources. Replicates
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are not ordered and cannot become an active access point for the cluster resource
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unless the <a href="../apis/clrgchgcrg.htm"><span class="apiname">Change
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Cluster Resource Group (QcstChangeClusterResourceGroup)</span> API</a> is
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used to change its role from replicate to peer. </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="rzaigconceptselements.htm" title="An iSeries cluster is a collection of one or more systems or partitions that work together as a single system. Use this information to understand the elements and their relationship to each other.">The elements of a cluster</a></div>
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</div>
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<div class="reltasks"><strong>Related tasks</strong><br />
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<div><a href="rzaigmanagechangesrolesrecoverydomain.htm" title="You can change the roles of nodes in a recovery domain for a cluster resource group, as well as add or remove nodes from a recovery domain. For a device cluster resource group, you can also change site name and data port IP addresses for a node in the recovery domain.">Change the recovery domain for a cluster resource group</a></div>
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<div><a href="rzaigmanageperformswitchover.htm" title="Performing a manual switchover causes the current primary node to switch over to the backup node, as defined in the cluster resource group's recovery domain.">Perform a switchover</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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