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From Jonathan Ellis <jbel...@gmail.com>
Subject Re: Cassandra hardware - balancing CPU/memory/iops/disk space
Date Sat, 06 Mar 2010 15:47:37 GMT
I think http://wiki.apache.org/cassandra/CassandraHardware answers
most of your questions.

If possible, it's definitely useful to try out a small fraction of
your anticipated workload against a test cluster, even a single node,
before finalizing your production hardware purchase.

On Sat, Mar 6, 2010 at 1:12 AM, Rosenberry, Eric
<eric.rosenberry@iovation.com> wrote:
> I am looking for advice from others that are further along in deploying
> Cassandra in production environments than we are.  I want to know what you
> are finding your bottlenecks to be.  I would feel silly purchasing dual
> processor quad core 2.93ghz Nehalem machines with 192 gigs of RAM just to
> find out that the two local SATA disks kept all that CPU and RAM from being
> useful (clearly that example would be a dumb).
>
>
>
> I need to spec out hardware for an “optimal” Cassandra node (though our
> read/write characteristics are not yet fully defined so let’s go with an
> “average” configuration).
>
>
>
> My main concern is finding the right balance of:
>
> ·         Available CPU
>
> ·         RAM amount
>
> ·         RAM speed (think Nehalem architecture where memory comes in a few
> speeds, though I doubt this is much of a concern as it is mainly dictated by
> which processor you buy and how many slots you populate)
>
> ·         Total iops available (i.e. number of disks)
>
> ·         Total disk space available (depending on the ratio of iops/space
> deciding on SAS vs. SATA and various rotational speeds)
>
>
>
> My current thinking is 1U boxes with four 3.5 inch disks since that seems to
> be a readily available config.  One big question is should I go with a
> single processor Nehalem system to go with those four disks, or would two
> CPU’s be useful, and also, how much RAM is appropriate to match?  I am
> making the assumption that Cassandra nodes are going to be disk bound as
> they must do a random read to answer any given query (i.e. indexes in RAM,
> but all data lives on disk?).
>
>
>
> The other big decision is what type of hard disks others are finding to
> provide the optimal ratio of iops to available space?  SAS or SATA?  And
> what rotational speed?
>
>
>
> Let me throw out here an actual hardware config and feel free to tell me the
> error of my ways:
>
> ·         A SuperMicro SuperServer 6016T-NTRF configured as follows:
>
> o   2.26 ghz E5520 dual processor quad core hyperthreaded Nehalem
> architecture (this proc provides a lot of bang for the buck, faster procs
> get more expensive quickly)
>
> o   Qty 12, 4 gig 1066mhz DIMMS for a total of 48 gigs RAM (the 4 gig DIMMS
> seem to be the price sweet spot)
>
> o   Dual on board 1 gigabit NIC’s (perhaps one for client connections and
> the other for cluster communication?)
>
> o   Dual power supplies (I don’t want to lose half my cluster due to a
> failure on one power leg)
>
> o   4x 1TB SATA disks (this is a complete SWAG)
>
> o   No RAID controller (all just single individual disks presented to the
> OS) – Though is there any down side to using a RAID controller with RAID 0
> (perhaps one single disk for the log for sequential io’s, and 3x disks in a
> stripe for the random io’s)
>
> o   The on-board IPMI based OOB controller (so we can kick the boxes
> remotely if need be)
>
> ·
> http://www.supermicro.com/products/system/1U/6016/SYS-6016T-NTRF.cfm
>
>
>
> I can’t help but think the above config has way too much RAM and CPU and not
> enough iops capacity.  My understanding is that Cassandra does not cache
> much in RAM though?
>
>
>
> Any thoughts are appreciated.  Thanks.
>
>
>
> -Eric
>
> _______________________________________________________________
> Eric Rosenberry
> Sr. Infrastructure Architect | Chief Bit Plumber
>
>
>
>
> iovation
> 111 SW Fifth Avenue
> Suite 3200
> Portland, OR 97204
> www.iovation.com
>
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