title: Cassandra datacenter replicaton versus Couchbase datacenter replication
body: <p>I'm trying to understand the difference between the datacenter replication implemented in Cassandra and in Couchbase. 
  It looks like in Cassandra, if I have two datacenters(DC), all my data is replicated in both. Whilst in Couchbase, two DCs hold different data and could be  manually configured the replication of a subset of data between different DCs. 
  Is it correct?</p>
  
  <p>How a client can know where  the data is located in Couchbase? If I query DC1 for a data holds in DC2, what happens?</p>
  
  <p>In Couchbase, how the whole system  is aware of where the data is replicated?</p>
  
  <p>Thank you in advance!</p>