From: Luke Lonergan <llonergan@greenplum.com>
To: Albert Cervera Areny <albert@sedifa.com>
To: pgsql-performance@postgresql.org
Subject: Re: Bad RAID1 read performance
Date: Wed, 30 May 2007 07:09:02 -0700
Message-ID: <C282D38E.31B6B%llonergan@greenplum.com> (raw)
In-Reply-To: <200705301135.32236.albert@sedifa.com>
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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To: pgsql-performance@postgresql.org
Cc: llonergan@greenplum.com, albert@sedifa.com
Subject: Re: Bad RAID1 read performance
In-Reply-To: <C282D38E.31B6B%llonergan@greenplum.com>
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