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From Dan Kinder <dkin...@turnitin.com>
Subject Multiple cassandra instances per physical node
Date Thu, 21 May 2015 17:32:26 GMT
Hi, I'd just like some clarity and advice regarding running multiple
cassandra instances on a single large machine (big JBOD array, plenty of
CPU/RAM).

First, I am aware this was not Cassandra's original design, and doing this
seems to unreasonably go against the "commodity hardware" intentions of
Cassandra's design. In general it seems to be recommended against (at least
as far as I've heard from @Rob Coli and others).

However maybe this term "commodity" is changing... my hardware/ops team
argues that due to cooling, power, and other datacenter costs, having
slightly larger nodes (>=32G RAM, >=24 CPU, >=8 disks JBOD) is actually a
better price point. Now, I am not a hardware guy, so if this is not
actually true I'd love to hear why, otherwise I pretty much need to take
them at their word.

Now, Cassandra features seemed to have improved such that JBOD works fairly
well, but especially with memory/GC this seems to be reaching its limit.
One Cassandra instance can only scale up so much.

So my question is: suppose I take a 12 disk JBOD and run 2 Cassandra nodes
(each with 5 data disks, 1 commit log disk) and either give each its own
container & IP or change the listen ports. Will this work? What are the
risks? Will/should Cassandra support this better in the future?

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