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From Jan Algermissen <jan.algermis...@nordsc.com>
Subject VM dimensions for running Cassandra and Hadoop
Date Wed, 31 Jul 2013 05:51:26 GMT
Hi,

thanks for the helpful replies last week.

It looks as if I will deploy Cassandra on a bunch of VMs and I am now in the process of understanding
what the dimensions of the VMS should be.

So far, I understand the following:

- I need at least 3 VMs for a minimal Cassandra setup
- I should get another VM to run the Hadoop job controller or
  can that run on one of the Cassandra VMs
- there is no point in giving the Cassandra JVMs more than
  8-12 GB heap space because of GC, so it seems going beyond 16GB
  RAM per VM makes no sense
- Each VM needs two disks, to separate commit log from data storage
- I must make sure the disks are directly attached, to prevent
  problems when multiple nodes flush the commit log at the
  same time
- I'll be having rather few writes and intend to hold most of the
  data in memory, so spinning disks are fine for the moment

Does that seem reasonable?

How should I plan the disk sizes and number of CPU cores?

Are there any other configuration mistakes to avoid?

Is there online documentation that discusses such VM sizing questions in more detail?

Jan






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