|Configuration / Configuring virtual nodes|
For production clusters, enabling virtual nodes (vnodes) has less impact on performance if you bring up a another data center configured with vnodes already enabled and let Cassandra automatic mechanisms distribute the existing data into the new nodes. Using the shuffle utility can be an expensive process on a running production system because the data to be shuffled around. Bootstrapping a new data center is a much safer way to enable vnodes.
This step ensures that after you move the client to the new data center that any previous writes are added to the new data center and that nothing else, such as hints, is dropped when you remove the old data center.