Multiple datacenter write requests 

How write requests work when using multiple datacenters.

In multiple datacenter deployments, Cassandra optimizes write performance by choosing one coordinator node. The coordinator node contacted by the client application forwards the write request to one replica in each of the other datacenters, with a special tag to forward the write to the other local replicas.

If using a write consistency level of LOCAL_ONE or LOCAL_QUORUM, only the nodes in the same data center as the coordinator node must respond to the client request in order for the request to succeed. This way, geographical latency does not impact client request response times.