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From Jonathan Ellis <jbel...@gmail.com>
Subject Re: Cassandra hardware - balancing CPU/memory/iops/disk space
Date Sun, 07 Mar 2010 19:05:05 GMT
Yes, but I would guess 90% of workloads are better served with
spending the extra money on more machines w/ cheap sata disks and lots
of ram.

-Jonathan

On Sun, Mar 7, 2010 at 1:00 PM, Boris Shulman <shulmanb@gmail.com> wrote:
> Do you think having SAS disks will give better performance?
>
> On Sat, Mar 6, 2010 at 5:47 PM, Jonathan Ellis <jbellis@gmail.com> wrote:
>> 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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>>
>

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