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RAID stripe size question

From: "Mikael Carneholm" <Mikael(dot)Carneholm(at)WirelessCar(dot)com>
To: <pgsql-performance(at)postgresql(dot)org>
Subject: RAID stripe size question
Date: 2006-07-16 22:52:17
Message-ID: 7F10D26ECFA1FB458B89C5B4B0D72C2B4E4BB1@sesrv12.wirelesscar.com (view raw or flat)
Thread:
Lists: pgsql-performance
I have finally gotten my hands on the MSA1500 that we ordered some time
ago. It has 28 x 10K 146Gb drives, currently grouped as 10 (for wal) +
18 (for data). There's only one controller (an emulex), but I hope
performance won't suffer too much from that. Raid level is 0+1,
filesystem is ext3. 

Now to the interesting part: would it make sense to use different stripe
sizes on the separate disk arrays? In theory, a smaller stripe size
(8-32K) should increase sequential write throughput at the cost of
decreased positioning performance, which sounds good for WAL (assuming
WAL is never "searched" during normal operation). And for disks holding
the data, a larger stripe size (>32K) should provide for more concurrent
(small) reads/writes at the cost of decreased raw throughput. This is
with an OLTP type application in mind, so I'd rather have high
transaction throughput than high sequential read speed. The interface is
a 2Gb FC so I'm throttled to (theoretically) 192Mb/s, anyway.

So, does this make sense? Has anyone tried it and seen any performance
gains from it?

Regards,
Mikael.

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Next:From: Steinar H. GundersonDate: 2006-07-16 23:10:05
Subject: Re: RAID stripe size question
Previous:From: Joe ConwayDate: 2006-07-16 18:08:07
Subject: Re: Big differences in plans between 8.0 and 8.1

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