title: How to deal with Split Brain with an cluster have the two number of nodes?
body: <p>I am leaning some basic concept of cluster computing and I have some questions to ask.</p>
  
  <p>According to <a href="http://clusterlabs.org/doc/en-US/Pacemaker/1.1/html/Clusters_from_Scratch/_perform_a_failover.html" rel="nofollow noreferrer">this article:</a></p>
  
  <p>If a cluster splits into two (or more) groups of nodes that can no longer communicate with each other (aka.partitions), quorum is used to prevent resources from starting on more nodes than desired, which would risk data corruption.
  A cluster has quorum when more than half of all known nodes are online in the same partition, or for the mathematically inclined, whenever the following equation is true:</p>
  
  <p><strong><code>total_nodes &lt; 2 * active_nodes</code></strong></p>
  
  <p>For example, if a 5-node cluster split into 3- and 2-node paritions, the 3-node partition would have quorum and could continue serving resources. If a 6-node cluster split into two 3-node partitions, neither partition would have quorum; pacemaker’s default behavior in such cases is to stop all resources, in order to prevent data corruption.</p>
  
  <p><strong>Two-node clusters are a special case</strong>. 
  By the above definition, a two-node cluster would only have quorum when both nodes are running. This would make the creation of a two-node cluster pointless</p>
  
  <p><strong>Questions:</strong></p>
  
  <p>From above,I came out with some confuse, why we can not stop all cluster resources like “<strong>6-node cluster</strong>”?What`s the special lies in the two node cluster?</p>