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From Per Olesen <...@trifork.com>
Subject Running a very small cluster
Date Wed, 09 Jun 2010 19:59:20 GMT
Short question: Do cassandra only *really* shine when running a cluster with lots of nodes?

Same question in a lengthy version:

If what I want to obtain from my cassandra cluster is given as this:
a) protection against data loss if nodes disk-crash
b) good uptime, if servers become unavailable or are taken down for service
c) good read performance

(notice: I do not need exceptionally good write performance)

So, if I setup a cluster with 3 nodes only, and set ReplicationFactor=3, and use QUORUM reads
and writes, do I then have a chance of obtaining my goal?

Or do I need a cassandra cluster with "lots" of nodes? I have no number for what I mean with
"lots", but I regard 2-3 nodes as NOT being a lot :-) 
(I know there are many variables here, but bear with me).

Here are my thoughts:

With respect to (a): 
RF=3 will mean all (3) nodes with have all data on them, which I think of as "good enough
protection". So, goal reached on that one.

But what about (b): 
With QUOROM reads and writes and RF=3, I can take down one and only one node at any time,
and still be up and running, right? If correct, I guess this is up to me, if that is okay
:)

Last, on (c): 
Given that what we are aiming at is good read performance, does it then make much sense, to
run a cassandra cluster if we only plan on having 3 nodes? I mean, then there won't be that
many nodes to distribute reads to?

/Per


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