From: Mark Kirkwood <mark.kirkwood@catalyst.net.nz>
To: pgsql-performance@postgresql.org
Subject: Re: Advice configuring ServeRAID 8k for performance
Date: Fri, 06 Aug 2010 12:35:44 +1200
Message-ID: <4C5B58E0.9060902@catalyst.net.nz> (raw)
In-Reply-To: <4C5B57F6.8070104@catalyst.net.nz>
References: <op.vgy9k5ov5ru9c3@kent60.office.vivox.com>
<4C5B4A0C.5080508@catalyst.net.nz>
<201008051658.13399@hal.medialogik.com>
<4C5B57F6.8070104@catalyst.net.nz>
On 06/08/10 12:31, Mark Kirkwood wrote:
> On 06/08/10 11:58, Alan Hodgson wrote:
>> On Thursday, August 05, 2010, Mark
>> Kirkwood<mark.kirkwood@catalyst.net.nz>
>> wrote:
>>> Normally I'd agree with the others and recommend RAID10 - but you say
>>> you have an OLAP workload - if it is *heavily* read biased you may get
>>> better performance with RAID5 (more effective disks to read from).
>>> Having said that, your sequential read performance right now is pretty
>>> low (151 MB/s - should be double this), which may point to an issue
>>> with this controller. Unfortunately this *may* be important for an OLAP
>>> workload (seq scans of big tables).
>> Probably a low (default) readahead limitation. ext3 doesn't help but
>> it can
>> usually get up over 400MB/sec. Doubt it's the controller.
>>
>
> Yeah - good suggestion, so cranking up readahead (man blockdev) and
> retesting is recommended.
>
>
... sorry, it just occurred to wonder about the stripe or chunk size
used in the array, as making this too small can also severely hamper
sequential performance.
Cheers
Mark
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To: pgsql-performance@postgresql.org
Cc: mark.kirkwood@catalyst.net.nz
Subject: Re: Advice configuring ServeRAID 8k for performance
In-Reply-To: <4C5B58E0.9060902@catalyst.net.nz>
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