title: Cassandra nodetool repair best practices
body: <p>This question applies to Cassandra 2.2</p>
  
  <p>I am embarrassed to say that I still do not understand when I should be running a <code>nodetool repair</code>, or to be more precise on which nodes.</p>
  
  <p>So far, I understand that to ensure deletes are handled correctly I should be running a <strong>repair</strong> at a frequency that is less than the <code>GC_GRACE_SECONDS</code>. So that's cool got that bit.</p>
  
  <p>Q. If I have a cluster of 9 nodes with a replication factor of 3, what type of repair do I run? more importantly do I run the repair on <strong>every</strong> node, or just one node?</p>
  
  <p>Q. If I have multiple data centers, does that change how I run repairs. Do I have to run them in each DC, or can it be <em>coordinated</em> from just one node in one DC?</p>
  
  <p>I am hoping this is a trivial question and someone can just tell it how it is.</p>