What is replication factor in cassandra and how does it affect single DC or multiple DC nodes ?
Cassandra stores replicas on multiple nodes to ensure reliability and fault tolerance. The total number of replicas across the cluster is referred to as the replication factor. A replication factor of 1 means that there is only one copy of each row on one node. A replication factor of 2 means two copies of each row, where each copy is on a different node. All replicas are equally important; there is no primary or master replica
When creating keyspace, you need to specify the replication factor on each DC.
Example Single DC with SimpleStrategy:
CREATE KEYSPACE Excelsior WITH REPLICATION = { 'class' : 'SimpleStrategy', 'replication_factor' : 3 };
Example Multi DC :
CREATE KEYSPACE Excalibur WITH REPLICATION = {'class' : 'NetworkTopologyStrategy', 'dc1' : 3, 'dc2' : 2};