From: Mark Kirkwood <markir@paradise.net.nz>
To: Greg Smith <gsmith@gregsmith.com>
Cc: pgsql-performance@postgresql.org <pgsql-performance@postgresql.org>
Subject: Re: Raid 10 chunksize
Date: Thu, 02 Apr 2009 19:31:11 +1300
Message-ID: <49D45BAF.7050709@paradise.net.nz> (raw)
In-Reply-To: <alpine.GSO.2.01.0903261309220.7258@westnet.com>
References: <49C98433.5080709@paradise.net.nz>
<alpine.GSO.2.01.0903250251490.13683@westnet.com>
<49CB066C.5040203@paradise.net.nz>
<alpine.GSO.2.01.0903261309220.7258@westnet.com>
Greg Smith wrote:
>
>> Yeah - with 64K chunksize I'm seeing a result more congruent with
>> yours (866 or so for 24 clients)
>
> That's good to hear. If adjusting that helped so much, you might
> consider aligning the filesystem partitions to the chunk size too; the
> partition header usually screws that up on Linux. See these two
> references for ideas:
> http://www.vmware.com/resources/techresources/608
> http://spiralbound.net/2008/06/09/creating-linux-partitions-for-clariion
>
Well I went away and did this (actually organized for for the system
folks to...). Retesting showed no appreciable difference (if anything
slower). Then I got to thinking:
For a partition created on a (hardware) raided device, sure - alignment
is very important, however in my case we are using software (md) raid -
which creates devices out of individual partitions (which are on
individual SAS disks) e.g:
md3 : active raid10 sda4[0] sdd4[3] sdc4[2] sdb4[1]
177389056 blocks 256K chunks 2 near-copies [4/4] [UUUU]
I'm thinking that alignment issues do not apply here, as md will
allocate chunks starting at the beginning of wherever sda4 (etc) begins
- so the absolute starting position of sda4 is irrelevant. Or am I
missing something?
Thanks again
Mark
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To: pgsql-performance@postgresql.org
Cc: markir@paradise.net.nz, gsmith@gregsmith.com
Subject: Re: Raid 10 chunksize
In-Reply-To: <49D45BAF.7050709@paradise.net.nz>
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