Replicas and replication
Replicas are copies of data that are proved on another node in a cluster.
In addition to distributing information across the cluster for even data distribution and cluster performance, you can also establish replica vBuckets within a single Couchbase cluster.
A copy of data from one bucket, known as a source is copied to a destination, which we also refer to as the replica, or replica vBucket. The node that contains the replica vBucket is also referred to as the replica node while the node containing original data to be replicated is called a source node. Distribution of replica data is handled in the same way as data at a source node; portions of replica data will be distributed around the cluster to prevent a single point of failure.
After Couchbase has stored replica data at a destination node, the data will also be placed in a queue to be persisted on disk at that destination node.
When replication is performed between two Couchbase clusters, it is called Cross Data Center Replication (XDCR). Use cases for XDCR are to copy your data on a cluster that is closer to your users, or to backup data in case of disaster recovery.