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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>7.3. Manual split brain recovery</title><link rel="stylesheet" type="text/css" href="default.css" /><meta name="generator" content="DocBook XSL Stylesheets V1.78.1" /><link rel="home" href="drbd-users-guide.html" title="The DRBD User’s Guide" /><link rel="up" href="ch-troubleshooting.html" title="Chapter 7. Troubleshooting and error recovery" /><link rel="prev" href="s-node-failure.html" title="7.2. Dealing with node failure" /><link rel="next" href="p-apps.html" title="Part IV. DRBD-enabled applications" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">7.3. Manual split brain recovery</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="s-node-failure.html">Prev</a> </td><th width="60%" align="center">Chapter 7. Troubleshooting and error recovery</th><td width="20%" align="right"> <a accesskey="n" href="p-apps.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-resolve-split-brain"></a>7.3. Manual split brain recovery</h2></div></div></div><p><a id="idp53417232" class="indexterm"></a>DRBD detects split brain at the time
connectivity becomes available again and the peer nodes exchange the
initial DRBD protocol handshake. If DRBD detects that both nodes are
(or were at some point, while disconnected) in the primary role, it
immediately tears down the replication connection. The tell-tale sign
of this is a message like the following appearing in the system log:</p><pre class="screen">Split-Brain detected, dropping connection!</pre><p>After split brain has been detected, one node will always have the
resource in a <a id="idp53420000" class="indexterm"></a><a id="idp53420880" class="indexterm"></a><code class="literal">StandAlone</code> connection state. The
other might either also be in the <code class="literal">StandAlone</code> state (if both nodes
detected the split brain simultaneously), or in
<a id="idp53423296" class="indexterm"></a> <a id="idp53424304" class="indexterm"></a><code class="literal">WFConnection</code> (if the peer tore down the connection before the
other node had a chance to detect split brain).</p><p>At this point, unless you configured DRBD to automatically recover
from split brain, you must manually intervene by selecting one node
whose modifications will be discarded (this node is referred to as the
<a id="idp53426688" class="indexterm"></a><span class="emphasis"><em>split brain victim</em></span>). This intervention is
made with the following commands:</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>The split brain victim needs to be in the connection state of
<code class="literal">StandAlone</code> or the following commands will return an error.
You can ensure it is standalone by issuing:</p><pre class="screen">drbdadm disconnect <resource></pre></td></tr></table></div><pre class="screen">drbdadm secondary <resource>
drbdadm connect --discard-my-data <resource></pre><p>On the other node (the <a id="idp53431616" class="indexterm"></a><span class="emphasis"><em>split brain survivor</em></span>),
if its connection state is also <code class="literal">StandAlone</code>, you would enter:</p><pre class="screen">drbdadm connect <resource></pre><p>You may omit this step if the node is already in the
<code class="literal">WFConnection</code> state; it will then reconnect automatically.</p><p>If the resource affected by the split brain is a
<a class="link" href="s-three-nodes.html" title="6.18. Creating a three-node setup">stacked resource</a>, use <code class="literal">drbdadm --stacked</code> instead
of just <code class="literal">drbdadm</code>.</p><p>Upon connection, your split brain victim immediately changes its
connection state to <code class="literal">SyncTarget</code>, and has its modifications
overwritten by the remaining primary node.</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>The split brain victim is not subjected to a full device
synchronization. Instead, it has its local modifications rolled back,
and any modifications made on the split brain survivor propagate to
the victim.</p></td></tr></table></div><p>After re-synchronization has completed, the split brain is considered
resolved and the two nodes form a fully consistent, redundant
replicated storage system again.</p></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="s-node-failure.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="ch-troubleshooting.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="p-apps.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">7.2. Dealing with node failure </td><td width="20%" align="center"><a accesskey="h" href="drbd-users-guide.html">Home</a></td><td width="40%" align="right" valign="top"> Part IV. DRBD-enabled applications</td></tr></table></div></body></html>
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