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<h1 class="topictitle1">Example: A four-node cluster</h1>
<div><p>Use this example to create a more complex cluster that contains
four nodes.</p>
<p>This example configuration provides the following:</p>
<ul><li>Two-way replication and failover</li>
<li>Three-tier environment</li>
<li>Applications and data move independently</li>
<li>Backup is used for normal production of different workload</li>
</ul>
<br /><img src="rzaig504.gif" alt="A four-node cluster featuriing two application CRGs and two data CRGs." /><br /><p>The four-node example shows the additional flexibility that is possible
with an iSeries™ cluster.
There are two application cluster resource groups (A1 and A2) and two data
cluster resource groups (D1 and D2). The data associated with D1 is the critical
data for the application associated with A1. The data associated with D2 is
the critical data for the application associated with A2. Because this is
a three-tier environment, the applications exist on the second tier (Node
L2 and Node R2) and the data is separated into the third tier (Node L3 and
Node R3).</p>
<div class="tablenoborder"><table cellpadding="4" cellspacing="0" summary="" frame="border" border="1" rules="all"><thead align="left"><tr><th valign="top" id="d0e39">Cluster resource group (CRG)</th>
<th valign="top" id="d0e41">Primary</th>
<th valign="top" id="d0e43">Backup</th>
</tr>
</thead>
<tbody><tr><td valign="top" headers="d0e39 ">Application CRG A1</td>
<td valign="top" headers="d0e41 ">L2</td>
<td valign="top" headers="d0e43 ">R2</td>
</tr>
<tr><td valign="top" headers="d0e39 ">Application CRG A2</td>
<td valign="top" headers="d0e41 ">R2</td>
<td valign="top" headers="d0e43 ">L2</td>
</tr>
<tr><td valign="top" headers="d0e39 ">Data CRG D1</td>
<td valign="top" headers="d0e41 ">R3</td>
<td valign="top" headers="d0e43 ">L3</td>
</tr>
<tr><td valign="top" headers="d0e39 ">Data CRG D2</td>
<td valign="top" headers="d0e41 ">L3</td>
<td valign="top" headers="d0e43 ">R3</td>
</tr>
</tbody>
</table>
</div>
<p>This enables mutual take-over capability at both the application and data
levels. All four nodes are being used for normal production. They are also
being used to back up other systems in the cluster. The two applications and
their associated data should always be available in this cluster. The outage
of any single node will not disrupt availability. In addition, the simultaneous
outage of a node at the application level with a node at the data level will
not disrupt availability.</p>
<div class="note"><span class="notetitle">Note:</span> In either instance, the cluster is running exposed in that some cluster
resources will not be replicated while a node is down. You can resolve this
by having more than one backup for any critical cluster resource.</div>
</div>
<div>
<div class="familylinks">
<div class="parentlink"><strong>Parent topic:</strong> <a href="rzaigscenarios.htm" title="Use these examples of typical cluster implementations to understand when, why, and how using clusters can be beneficial.">Examples: Cluster configurations</a></div>
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