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Date: Fri, 13 Jul 2012 13:01:28 +0530
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Subject: Re: Using a node in separate cluster without decommissioning.
From: rohit bhatia <rohit2412@gmail.com>
To: user@cassandra.apache.org
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Hi

Just wanted to say that it worked. I also made sure to modify thrift
rpc_port and storage port so that the two clusters don't interfere.
Thanks for the suggestion

Thanks
Rohit

On Thu, Jul 12, 2012 at 10:01 AM, aaron morton <aaron@thelastpickle.com> wrote:
> 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
>
>