> Since replication factor is 2 in first cluster, I > won't lose any data. Assuming you have been running repair or working at CL QUORUM (which is the same as CL ALL for RF 2)
> Is it advisable and safe to go ahead? um, so the plan is to turn off 2 nodes in the first cluster, restask them into the new cluster and then reverse the process ? If you simply turn two nodes off in the first cluster you will have reduce the availability for a portion of the ring. 25% of the keys will now have at best 1 node they can be stored on. If a node is having any sort of problems, and it's is a replica for one of the down nodes, the cluster will appear down for 12.5% of the keyspace. If you work at QUORUM you will not have enough nodes available to write / read 25% of the keys. If you decomission the nodes, you will still have 2 replicas available for each key range. This is the path I would recommend. If you _really_ need to do it what you suggest will probably work. Some tips: * do safe shutdowns - nodetool disablegossip, disablethrift, drain * don't forget to copy the yaml file. * in the first cluster the other nodes will collect hints for the first hour the nodes are down. You are not going to want these so disable HH. * get the nodes back into the first cluster before gc_grace_seconds expires. * bring them back and repair them. * when you bring them back, reading at CL ONE will give inconsistent results. Reading at QUOURM may result in a lot of repair activity. Hope that helps. ----------------- Aaron Morton Freelance Developer @aaronmorton http://www.thelastpickle.com On 11/07/2012, at 6:35 AM, rohit bhatia wrote: > Hi > > I want to take out 2 nodes from a 8 node cluster and use in another > cluster, but can't afford the overhead of streaming the data and > rebalance cluster. Since replication factor is 2 in first cluster, I > won't lose any data. > > I'm planning to save my commit_log and data directories and > bootstrapping the node in the second cluster. Afterwards I'll just > replace both the directories and join the node back to the original > cluster. This should work since cassandra saves all the cluster and > schema info in the system keyspace. > > Is it advisable and safe to go ahead? > > Thanks > Rohit
