I created to explore doing that - it would seem like a reasonable thing to do with a batch/analytic/MR operation.  You might chime in to explain your use case on the ticket.

https://issues.apache.org/jira/browse/CASSANDRA-1821

On Dec 3, 2010, at 2:33 PM, Sanjay Acharya wrote:

We are in the process of evaluating Cassandra for our needs and we expect to use parallelism for analytics on collected data. The following BLOG mentions that 
Cassandra's Map-Reduce support does not support multiple column families http://allthingshadoop.com/2010/04/24/running-hadoop-mapreduce-with-cassandra-nosql/

Has the same proven to be a challenge or blockers for those using the Map-Reduce functionality? Please share your experience. Also are there plans to support multiple column family map-reduce functionality?