Can I just copy data files for the required keyspaces, create schema manually and run repair? 
If you have something like RF 3 and 3 nodes then yes, you can copy the data from one node in the source cluster to all nodes in the dest cluster and use cleanup to remove the unneeded data. Because each node in the source cluster has a full copy of the data.  

If that's not the case you cannot copy the data files, even if they have the same number of nodes, because the nodes in the dest cluster will have different tokens. AFAIK you need to export the full data set from the source DC and then import it into the dest system. 

The Bulk Load utility may be of help http://www.datastax.com/docs/1.2/references/bulkloader . You could copy the SSTables from every node in the source system and bulk load them into the dest system. That process will ensure rows are sent to nodes that are replicas. 

Cheers

-----------------
Aaron Morton
Freelance Cassandra Consultant
New Zealand

@aaronmorton

On 9/07/2013, at 12:45 PM, Baskar Duraikannu <baskar.duraikannu.db@gmail.com> wrote:

We have two clusters used by two different groups with vnodes enabled. Now there is a need to move some of the keyspaces from cluster 1 to cluster 2.

Can I just copy data files for the required keyspaces, create schema manually and run repair?

Anything else required?  Please help.
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Thanks,
Baskar Duraikannu