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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>6.18. Creating a three-node setup</title><link rel="stylesheet" type="text/css" href="default.css" /><meta name="generator" content="DocBook XSL Stylesheets V1.79.1" /><link rel="home" href="drbd-users-guide.html" title="The DRBD User’s Guide" /><link rel="up" href="ch-admin.html" title="Chapter 6. Common administrative tasks" /><link rel="prev" href="s-configure-split-brain-behavior.html" title="6.17. Configuring split brain behavior" /><link rel="next" href="s-using-drbd-proxy.html" title="6.19. Using DRBD Proxy" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">6.18. Creating a three-node setup</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="s-configure-split-brain-behavior.html">Prev</a> </td><th width="60%" align="center">Chapter 6. Common administrative tasks</th><td width="20%" align="right"> <a accesskey="n" href="s-using-drbd-proxy.html">Next</a></td></tr></table><hr /></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="s-three-nodes"></a>6.18. Creating a three-node setup</h2></div></div></div><p>A three-node setup involves one DRBD device <span class="emphasis"><em>stacked</em></span> atop another.</p><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="s-stacking-considerations"></a>6.18.1. Device stacking considerations</h3></div></div></div><p>The following considerations apply to this type of setup:</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
The stacked device is the active one. Assume you have configured one
DRBD device <code class="literal">/dev/drbd0</code>, and the stacked device atop it is
<code class="literal">/dev/drbd10</code>, then <code class="literal">/dev/drbd10</code> will be the device that you mount
and use.
</li><li class="listitem">
Device meta data will be stored twice, on the underlying DRBD device
<span class="emphasis"><em>and</em></span> the stacked DRBD device. On the stacked device, you must always
use <a class="link" href="ch-internals.html#s-internal-meta-data" title="17.1.1. Internal meta data">internal meta data</a>. This means that the
effectively available storage area on a stacked device is slightly
smaller, compared to an unstacked device.
</li><li class="listitem">
To get the stacked upper level device running, the underlying device
must be in the primary role.
</li><li class="listitem">
To be able to synchronize the backup node, the stacked device on the
active node must be up and in the primary role.
</li></ul></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="s-three-node-config"></a>6.18.2. Configuring a stacked resource</h3></div></div></div><p>In the following example, nodes are named <code class="literal">alice</code>, <code class="literal">bob</code>, and
<code class="literal">charlie</code>, with <code class="literal">alice</code> and <code class="literal">bob</code> forming a two-node cluster, and
<code class="literal">charlie</code> being the backup node.</p><pre class="programlisting">resource r0 {
net {
protocol C;
}
on alice {
device /dev/drbd0;
disk /dev/sda6;
address 10.0.0.1:7788;
meta-disk internal;
}
on bob {
device /dev/drbd0;
disk /dev/sda6;
address 10.0.0.2:7788;
meta-disk internal;
}
}
resource r0-U {
net {
protocol A;
}
stacked-on-top-of r0 {
device /dev/drbd10;
address 192.168.42.1:7788;
}
on charlie {
device /dev/drbd10;
disk /dev/hda6;
address 192.168.42.2:7788; # Public IP of the backup node
meta-disk internal;
}
}</pre><p>As with any <code class="literal">drbd.conf</code> configuration file, this must be distributed
across all nodes in the cluster — in this case, three nodes. Notice
the following extra keyword not found in an unstacked resource
configuration:</p><p><strong><code class="literal">stacked-on-top-of</code>. </strong>This option informs DRBD that the resource which contains it is a
stacked resource. It replaces one of the <code class="literal">on</code> sections normally found
in any resource configuration. Do not use <code class="literal">stacked-on-top-of</code> in an
lower-level resource.</p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><table border="0" summary="Note"><tr><td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="images/note.png" /></td><th align="left">Note</th></tr><tr><td align="left" valign="top"><p>It is not a requirement to use <a class="link" href="s-replication-protocols.html#fp-protocol-a" title="Protocol A">Protocol A</a> for
stacked resources. You may select any of DRBD’s replication protocols
depending on your application.</p></td></tr></table></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="s-three-node-enable"></a>6.18.3. Enabling stacked resources</h3></div></div></div><p>To enable a stacked resource, you first enable its lower-level
resource and promote it:</p><pre class="screen">drbdadm up r0
drbdadm primary r0</pre><p>As with unstacked resources, you must create DRBD meta data on the
stacked resources. This is done using the following command:</p><pre class="screen"># drbdadm create-md --stacked r0-U</pre><p>Then, you may enable the stacked resource:</p><pre class="screen"># drbdadm up --stacked r0-U
# drbdadm primary --stacked r0-U</pre><p>After this, you may bring up the resource on the backup node, enabling
three-node replication:</p><pre class="screen"># drbdadm create-md r0-U
# drbdadm up r0-U</pre><p>In order to automate stacked resource management, you may integrate
stacked resources in your cluster manager configuration. See
<a class="xref" href="s-pacemaker-stacked-resources.html" title="8.4. Using stacked DRBD resources in Pacemaker clusters">Section 8.4, “Using stacked DRBD resources in Pacemaker clusters”</a> for information on doing this in a
cluster managed by the Pacemaker cluster management framework.</p></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="s-configure-split-brain-behavior.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="ch-admin.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="s-using-drbd-proxy.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">6.17. Configuring split brain behavior </td><td width="20%" align="center"><a accesskey="h" href="drbd-users-guide.html">Home</a></td><td width="40%" align="right" valign="top"> 6.19. Using DRBD Proxy</td></tr></table></div></body></html>
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