Message-ID: <4FBDC040.2000406@catalyst.net.nz>
Date: Thu, 24 May 2012 16:59:44 +1200
From: Mark Kirkwood <mark.kirkwood@catalyst.net.nz>
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To: Jan Nielsen <jan.sture.nielsen@gmail.com>
CC: pgsql-performance@postgresql.org
Subject: Re: Configuration Recommendations
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On 20/05/12 03:47, Jan Nielsen wrote:
> In this test, the local mount's buffered reads perform best around RA~10k @
> 150MB/sec then starts a steady decline. The SAN mount has a similar but
> more subtle decline with a maximum around RA~5k @ 80MB/sec but with much
> greater variance. I was surprised at the 80MB/sec for the SAN - I was
> expecting 150MB/sec - and I'm also surprised at the variance. I understand
> that there are many more elements involved for the SAN: more drives,
> network overhead&  latency, iscsi, etc. but I'm still surprised.
>
> Is this expected behavior for a SAN mount or is this a hint at some
> misconfiguration? Thoughts?
>
>

Is the SAN mount via iSCSI?  If so and also if the connection is a 
single 1Gbit interface then 80MB/s is reasonable. You might get closer 
to 100MB/s by tweaking things like MTU for the interface concerned, but 
to get more performance either bonding several 1Gbit links or using 
10Gbit is required.

Regards

Mark