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From Jon Haddad <...@jonhaddad.com>
Subject Re: Cassandra cluster migration in Amazon EC2
Date Mon, 02 Sep 2013 23:28:43 GMT
If you launch the new servers, have them join the cluster, then decommission the old ones,
you'll be able to do it without downtime.  It'll also have the effect of randomizing the tokens,
I believe. 

On Sep 2, 2013, at 4:21 PM, Renat Gilfanov <grennat@mail.ru> wrote:

> Hello,
> 
> Currently we have a Cassandra cluster in the Amazon EC2, and we are planning to upgrade
our deployment configuration to achieve better 
> performance and stability. However, a lot of open questions arise when planning this
migration. I'll be very thankfull if somebody could answer my 
> questions.
> 
> Current state:
> 
> We use Apache Cassandra 1.2.8, on 5 nodes deployed in the Amazon EC2, on m1.large instanses
with EBS volume each. In Cassandra we have set up 2 
> datacenters, first one have 3 nodes each in the separate rack, second - 2 nodes in the
separate rack, however all Amazon instances belong to the 
> same region and even availability zone. The replication factor for our keyspace is the
following: {'class': 'NetworkTopologyStrategy',  'DC2': '1',  'DC1': '2'}.
> We have virtual nodes enabled, however the shuffle hasn't been completed yet, and the
nodes unballanced.
> 
> What we want to achieve:
> 
> - We would like to move to the M1 Extra Large instances with 4x420 Gb instance storages.

> - Group 3 of storages into raid0 array, move data directory to the raid0, and commit
log - to the 4th left storage.
> 
> Open questions:
>  - Does the suggested configuration look reasonable from the performance optimization
point of view?
>  - As far as I understand, separation of commit log and data directory should make performance
better - but what about separation the OS from those two  - is it worth doing?
>  - What are the steps to perform such migration? Will it be possible to perform it without
downtime, restarting node by node with new configuration applied?
>  I'm especially worried about IP changes, when we'll uprade the instance type. What's
the recomended way to handle those IP changes?
> 
> Best Regards,
> Renat.


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