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From Renat Gilfanov <gren...@mail.ru>
Subject Cassandra cluster migration in Amazon EC2
Date Mon, 02 Sep 2013 23:21:34 GMT
 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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