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From Edward Capriolo <>
Subject Re: Running multiple instances on a single server --micrandra ??
Date Sat, 11 Dec 2010 04:39:18 GMT
On Thu, Dec 9, 2010 at 10:40 PM, Bill de hÓra <> wrote:
> 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

Having 6 IP's on a machine would be a given in this setup. That is not
an issue for me.

It is not "biting" me. We all know that going from 10-20 nodes is
pretty simple. However organic growth from 10-16, then a couple months
later from 16 - 22, can take some effort with 300-600 GB per node,
since each join and clean up can take a while. I am wondering if
dividing a single large node into multiple smaller instances would
make this type of growth easier.

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