Replica count overview

Replica count (also known as replication factor) is the number of Cassandra nodes to which you want the data to be written.

Replica count is the number of copies of data you want to be stored in your Cassandra cluster. Data replication is set on a keyspace definition - replication. A keyspace is a namespace container that defines how data is replicated on nodes. When you add a new data center, you might have to change the keyspace definition to set a replication policy for the new data center. You can read the keyspace definition by using CQLSH and the DESC KEYSPACE <NAME> command, where <NAME> can be one of {mailbox, gatekeeper, event, replication}. These definitions can be changed using an "ALTER KEYSPACE" command, but a nodetool repair operation must be run before any further usage of the Global Mailbox system or Cassandra cluster can commence safely.
Important: You can run the ALTER KEYSPACE command to adjust the replication factor on a per-data center basis, but you cannot change the name of the keyspace.