Hi all.

To move to a multi-dc setup, I am in the process of preparing our independent production DC's.

Part of this means moving from SimpleStragtegy (RF=5) to NetworkTopologyStrategy, but I'm still a bit confused as to some core aspects of replication.

The setup will be basic,
 - DC_NSW will contain 9 nodes in a single rack. 
 - DC_VIC will contain 9 nodes in a single rack
 - Initially the Replication Factor will be DC_NSW:5.
 - Once DC_VIC comes online, the Recplication Factor will be DC_NSW:5, DC_VIC:5

My understanding is that SimpleStrategy just 'walks the token ranges' to identify where to place replicas, whereas NetworkTopology will try to place the data in differing racks within the same datacenter (which will not be applicable to us given we have 1 rack per datacenter)

1. When does Cassandra walk the tokens/nodes to idenfity which hosts should contain replicas.  At every insert, Keyspace creation, Keyspace modification or ... ?
2. Is there a command or JMX entry that displays which ranges a server is repsonsible for (not its primary range, but ranges it is acting as a replica for) ?
3. Hypothetically, if we defined multiple racks per datacenter, and updated from Simple to Network
 - Then the replicas for a particular range may change ?
 - If so, how would Cassandra deal with this in a live environment ?

Thanks for your help

Matt