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From "Jacob, Arun" <>
Subject Cassandra Node Requirements
Date Wed, 24 Aug 2011 18:54:14 GMT
I'm trying to determine a node configuration for Cassandra. From what I've been able to determine
from reading around:

 1.  we need to cap data size at 50% of total node storage capacity for compaction
 2.  with RF=3, that means that I need to effectively assume that I have 1/6th of total storage
 3.  SSDs are preferred, but of course  reduce storage capacity
 4.  using standard storage means you bump up your RAM to keep as much in memory as possible.

Right now we are looking at storage requirements of 42 – 60TB, assuming a baseline of 3TB/day
and expiring data after 14-20 days (depending on use case),  I would assume based on above
that we need 252- 360TB total storage max.

My questions:

 1.  is 8TB (meaning 1.33 actual TB storage/node) a reasonable per node storage size for Cassandra?
I don’t want to use SSDs due to reduced storage capacity -- I don't want to buy 100s of
nodes to support that reduced storage capacity of SSDs.  Given that I will be using standard
drives, what is a reasonable/effective per node storage capacity?
 2.  other than splitting the commit log onto a separate drive, is there any other drive allocation
I should be doing?
 3.  Assuming I'm not using SSDs, what would be a good memory size for a node? I've heard
anything from 32-48 GB, but need more guidance.

Anything else that anyone has run into? What are common configurations being used by others?

Thanks in advance,

-- Arun

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