User-Agent: Microsoft-Entourage/11.3.3.061214
Date: Wed, 30 May 2007 07:09:02 -0700
Subject: Re: Bad RAID1 read performance
From: "Luke Lonergan" <llonergan@greenplum.com>
To: "Albert Cervera Areny" <albert@sedifa.com>,
	pgsql-performance@postgresql.org
Message-ID: <C282D38E.31B6B%llonergan@greenplum.com>
Thread-Topic: [PERFORM] Bad RAID1 read performance
Thread-Index: AceixBMJUa6mDw63Edy5oAAX8s8Cag==
In-Reply-To: <200705301135.32236.albert@sedifa.com>
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This sounds like a bad RAID controller - are you using a built-in hardware
RAID?  If so, you will likely want to use Linux software RAID instead.

Also - you might want to try a 512KB readahead - I've found that is optimal
for RAID1 on some RAID controllers.

- Luke 


On 5/30/07 2:35 AM, "Albert Cervera Areny" <albert@sedifa.com> wrote:

> Hi,
> after doing the "dd" tests for a server we have at work I obtained:
> Read: 47.20 Mb/s
> Write: 39.82 Mb/s
> Some days ago read performance was around 20Mb/s due to no readahead in md0
> so I modified it using hdparm. However, it seems to me that being it a RAID1
> read speed could be much better. These are SATA disks with 3Gb of RAM so I
> did 'time bash -c "dd if=/dev/zero of=bigfile bs=8k count=786432 && sync"'.
> File system is ext3 (if read many times in the list that XFS is faster), but
> I don't want to change the file system right now. Modifing the readahead from
> the current 1024k to 2048k doesn't make any difference. Are there any other
> tweaks I can make?
>  
> 
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