From: Jiri Horky <jiri.horky@cesnet.cz>
To: Erwan MAS <erwan@mas.nom.fr>
Cc: Caspar Smit <c.smit@truebit.nl>,
linux-raid@vger.kernel.org, fio@vger.kernel.org
Subject: Re: Striping does not increase performance.
Date: Mon, 12 Mar 2012 15:34:11 +0100 [thread overview]
Message-ID: <4F5E0963.6080708@cesnet.cz> (raw)
In-Reply-To: <20120312135847.GM4558@voyageur.mas.nom.fr>
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Hi,
as for alignment, please also check md metadata format version (-e
switch of mdadm). The version that ensures alignment is 1.0, which
places the metadata information to the back of the drive. I am not an
expert to LVM but I would suspect that there might be similar
problems/options to check.
I would first verify physical sector size of the drives you use. Please
have a look at the utility at
http://www.farm.particle.cz/blksztester.tar.gz. It randomly directly
writes e.g. 4K blocks to a block device at choosen alignment. Run it
with no arguments to get some help in English (README is in Czech :).
If you get similar speeds for 4k-align and 4k-misalign writes, the disk
use 512b physical sector size. The difference should be around 300% in
case of 4K sectors. You may try to google for sector size according to
product number, but I have seen cases where official vendor websites
were wrong. Please note that you shold not connect the drive under test
through RAID controller with its own logic and/or cache, which may skew
the results, but rather to a stupid motherboard.
I had several headaches with 4k-block drives in the past as well...
Cheers
Jiri Horky
On 03/12/2012 02:58 PM, Erwan MAS wrote:
> On Mon, Mar 12, 2012 at 02:02:36PM +0100, Caspar Smit wrote:
>> Hi Erwan,
>>
>> I do not use partitions on the drives so the whole disk /dev/sdb is
>> used as md component device, i was in the understanding that if not
>> using partitions the alignment is correct or am i wrong?
>>
> For me it's correct .
>
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next prev parent reply other threads:[~2012-03-12 14:34 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-03-12 12:34 Striping does not increase performance Caspar Smit
2012-03-12 12:57 ` Erwan MAS
2012-03-12 13:02 ` Caspar Smit
2012-03-12 13:58 ` Erwan MAS
2012-03-12 14:34 ` Jiri Horky [this message]
2012-03-12 16:23 ` John Robinson
2012-03-12 14:33 ` Peter Grandi
2012-03-13 11:44 ` Caspar Smit
2012-03-12 14:20 ` David Brown
2012-03-13 11:55 ` Caspar Smit
2012-03-13 14:12 ` David Brown
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