You have to use PropertyFileSnitch and NetworkTopologyStrategy to create a multi-datacenter setup with two circles. You can start reading from this page:
http://www.datastax.com/docs/1.0/cluster_architecture/replication#about-replica-placement-strategy

Moreover all tokens must be unique (even across datacenters), although - from pure curiosity - I wonder what is the rationale behind this.

By the way, can someone enlighten me about the first line in the output of the nodetool. Obviously it contains a token, but nothing else. It seems like a formatting glitch, but maybe it has a role.

On 2012.03.05. 11:06, Tamar Fraenkel wrote:
Hi!
I have a Cassandra  cluster with two nodes

nodetool ring -h localhost
Address         DC          Rack        Status State   Load            Owns    Token
                                                                               85070591730234615865843651857942052864
10.0.0.19       datacenter1 rack1       Up     Normal  488.74 KB       50.00%  0
10.0.0.28       datacenter1 rack1       Up     Normal  504.63 KB       50.00%  85070591730234615865843651857942052864

I want to create a second ring with the same name but two different nodes.
using tokengentool I get the same tokens as they are affected from the number of nodes in a ring.

My question is like this:
Lets say I create two new VMs, with IPs: 10.0.0.31 and 10.0.0.11
In 10.0.0.31 cassandra.yaml I will set
initial_token: 0
seeds: "10.0.0.31"
listen_address: 10.0.0.31
rpc_address: 0.0.0.0

In 10.0.0.11 cassandra.yaml I will set
initial_token: 85070591730234615865843651857942052864
seeds: "10.0.0.31"
listen_address: 10.0.0.11
rpc_address: 0.0.0.0 

Would the rings be separate?

Thanks,

Tamar Fraenkel 
Senior Software Engineer, TOK Media