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From Jan Algermissen <>
Subject VM dimensions for running Cassandra and Hadoop
Date Wed, 31 Jul 2013 05:51:26 GMT

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?


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