Date: Tue, 22 Nov 2005 09:29:47 +0100
To: Lars Roland <lroland@gmail.com>
Cc: Linux-Kernel <linux-kernel@vger.kernel.org>
Subject: Re: Poor Software RAID-0 performance with 2.6.14.2
Message-ID: <20051122082947.GA10890@aitel.hist.no>
References: <4ad99e050511211231o97d5d7fw59b44527dc25dcea@mail.gmail.com>
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From: Helge Hafting <helgehaf@aitel.hist.no>
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On Mon, Nov 21, 2005 at 09:31:14PM +0100, Lars Roland wrote:
> I have created a stripe across two 500Gb disks located on separate IDE
> channels using:
> 
> mdadm -Cv /dev/md0 -c32 -n2 -l0 /dev/hdb /dev/hdd
> 
> the performance is awful on both kernel 2.6.12.5 and 2.6.14.2 (even
> with hdparm and blockdev tuning), both bonnie++ and hdparm (included
> below) shows a single disk operating faster than the stripe:
> 
To rule out hardware problems (harware not as parallel as you might think):

Try running the performance test (bonnie++ or hdparm)
on both /dev/hdb and /dev/hdd at the same time. 

Two hdparms on different disks should not take longer time than one,
unless you have bad hardware.

One bonnie with size x MB takes y minutes to run.
Two bonnies, each of size x/2 MB should take between
y/2 an y minutes to run. If they need more, then something
is wrong again, explaining bad RAID performance.

Helge Hafting


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