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Message-ID: <493E61E1.1020303@sime.com>
Date: Tue, 09 Dec 2008 13:17:37 +0100
From: Mario Weilguni <mweilguni@sime.com>
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To: Alan Hodgson <ahodgson@simkin.ca>
CC: pgsql-performance@postgresql.org
Subject: Re: Experience with HP Smart Array P400 and SATA drives?
References: <4934FE60.30702@sime.com> <49395B57.EE98.0025.0@wicourts.gov>
	<200812051530.01258@hal.medialogik.com>
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Alan Hodgson schrieb:
>>>>> Mario Weilguni <mweilguni@sime.com> wrote:
>>>>>           
>>> strange values. An individual drive is capable of delivering 91
>>> MB/sec
>>>       
>>> sequential read performance, and we get values ~102MB/sec out of a
>>> 8-drive RAID5, seems to be ridiculous slow. 
>>>       
>
>
> What command are you using to test the reads?
>
> Some recommendations to try:
>
> 1) /sbin/blockdev --setra 2048 device (where device is the partition or LVM 
> volume)
>
> 2) Use XFS, and make sure your stripe settings match the RAID.
>
> Having said that, 102MB/sec sounds really low for any modern controller with 
> 8 drives, regardless of tuning or filesystem choice.
>
>   

First, thanks alot for this and all the other answers.

I measured the raw device performance:
dd if=/dev/cciss/c0d0 bs=64k count=100000 of=/dev/null

I get poor performance when all 8 drives are configured as one, large 
RAID-5, and slightly poorer performance when configured as JBOD. In 
production, we use XFS as FS, but I doubt this has anything to do with 
FS tuning.