The replication factor
On the surface, setting the replication factor seems to be a fundamentally straightforward idea. You configure Cassandra with the number of replicas you want to maintain (during keyspace creation), and the system dutifully performs the replication for you, thus protecting you when something goes wrong. So by defining a replication factor of three, you will end up with a total of three copies of the data. There are a number of variables in this equation, and we'll cover many of these in detail in this chapter. Let's start with the basic mechanics of setting the replication factor.
Replication strategies
One thing you'll quickly notice is that the semantics to set the replication factor depend on the replication strategy you choose. The replication strategy tells Cassandra exactly how you want replicas to be placed in the cluster.
There are two strategies available:
SimpleStrategy: This strategy is used for single data center deployments. It is fine to use...
