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From Bill de hÓra <b...@dehora.net>
Subject Re: Running multiple instances on a single server --micrandra ??
Date Fri, 10 Dec 2010 03:40:38 GMT


On Tue, 2010-12-07 at 21:25 -0500, Edward Capriolo wrote:

> The idea behind "micrandra" is for a 6 disk system run 6 instances of
> Cassandra, one per disk. Use the RackAwareSnitch to make sure no
> replicas live on the same node.
> 
> The downsides
> 1) we would have to manage 6x the instances of cassandra
> 2) we would have some overhead for each JVM.
> 
> The upsides ?
> 1) Since disk/instance failure only degrades the overall performance
> 1/6th (RAID0 you lost the entire node) (RAID5 still takes a hit when
> down a disk)
> 2) Moves and joins have less work to do
> 3) Can scale up a single node by adding a single disk to an existing
> system (assuming the ram and cpu is light)
> 4) OPP would be "easier" to balance out hot spots (maybe not on this
> one in not an OPP)
> 
> What does everyone thing? Does it ever make sense to run this way?


It might for read heavy loads.

When I looked at this, it was pointed out to me it's simpler to run
fewer bigger coarser nodes and take the entire node/server out when
something goes wrong. Basically give each Cassandra a server.

I wonder if it would be better to rethink compaction if that's what's
driving the idea. It seems to what is biting everyone, along with GC.

Bill

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