title: How to migrate single-token cluster to a new vnodes cluster without downtime?
body: <p>We have Cassandra cluster with single token per node, total 22 nodes, average load per node is 500Gb. It has SimpleStrategy for the main keyspace and SimpleSnitch.</p>
  
  <p>We need to migrate all data to the new datacenter and shutdown the old one without a downtime. New cluster has 28 nodes. I want to have vnodes on it.</p>
  
  <p>I'm thinking of the following process:</p>
  
  <ol>
  <li>Migrate the old cluster to vnodes </li>
  <li>Setup the new cluster with vnodes</li>
  <li>Add nodes from the new cluster to the old one and wait until it balances everything</li>
  <li>Switch clients to the new cluster </li>
  <li>Decommission nodes from the old cluster one by one</li>
  </ol>
  
  <p>But there are a lot of technical details. First of all, should I shuffle the old cluster after vnodes migration? Then, what is the best way to switch to NetworkTopologyStrategy and to GossipingPropertyFileSnitch? I want to switch to NetworkTopologyStrategy because new cluster has 2 different racks with separate power/network switches.</p>