Do you want to create two separate clusters or a single cluster with two data centres ? 

If it's the later, token selection is discussed here http://www.datastax.com/docs/1.0/install/cluster_init#token-gen-cassandra
 
Moreover all tokens must be unique (even across datacenters), although - from pure curiosity - I wonder what is the rationale behind this.
Otherwise data is not evenly distributed.

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. 
It's the exclusive lower bound token for the first node in the ring. This also happens to be the token for the last node in the ring. 

In your setup 
10.0.0.19 "owns" (85070591730234615865843651857942052864+1) to 0
10.0.0.28 "owns"  (0 + 1) to 85070591730234615865843651857942052864

(does not imply primary replica, just used to map keys to nodes.)
 


-----------------
Aaron Morton
Freelance Developer
@aaronmorton

On 5/03/2012, at 11:38 PM, Hontvári József Levente wrote:

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 

<Mail Attachment.png>