title: Cassandra - Understanding Rack Concept on PropertyFileSnitch example
body: <p>I am working on multi DC deployment and one thing is not clear to me - this is the rack concept interpretation from Cassandra perspective.</p>
  
  <p>I can enforce replication order by defining proper key ranges. Why do I need to specify racks additionally in <code>cassandra-topology.properties</code> ? </p>
  
  <p>Lets take as example Cassandra documentation: <a href="http://www.datastax.com/docs/1.1/cluster_architecture/replication" rel="nofollow">http://www.datastax.com/docs/1.1/cluster_architecture/replication</a></p>
  
  <p>If I have replication factor 3, and my row key is stored on Node 1, than replicas will be stored on Node 2 and 3 - this is obvious when we look on ring structure, so... why do I need to duplicate this information in rack configuration?</p>