From: Peter Rabbitson <rabbit+list@rabbit.us>
To: "Keld Jørn Simonsen" <keld@dkuug.dk>
Cc: thomas62186218@aol.com, soltys@ziu.info, mauermann@gmail.com,
linux-raid@vger.kernel.org
Subject: Re: LVM on raid10,f2 performance issues
Date: Mon, 19 Jan 2009 13:24:39 +0100 [thread overview]
Message-ID: <49747107.8020607@rabbit.us> (raw)
In-Reply-To: <20090119121724.GA23623@rap.rap.dk>
Keld Jørn Simonsen wrote:
> Hmm,
>
> Why is the command
>
> blockdev --setra 65536 /dev/md0
>
> really needed? I think the kernel should set a reasonable default here.
The in-kernel default for a block device is 256 (128k) which is way too
low. the MD subsystems tries to be a bit smarter and assigns the md
device readahead according to the number of devices/raid level. For
streaming (i.e. file sever) these values are also too low. LVs can take
a readahead specification at creation time and use that, but this is
manual.
It is arguable what the typical workload is, but I would lean towards
big long linear reads (fileserver) vs short scattered ones (database).
The real solution to the problem was proposed a long time ago, and it
seems it got lost in the attic: http://lwn.net/Articles/155510/
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next prev parent reply other threads:[~2009-01-19 12:24 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-12-01 0:00 LVM on raid10,f2 performance issues Holger Mauermann
2008-12-01 16:42 ` Keld Jørn Simonsen
2008-12-02 23:28 ` Holger Mauermann
2008-12-03 7:15 ` Keld Jørn Simonsen
2008-12-03 9:43 ` Michal Soltys
2009-01-19 1:24 ` thomas62186218
2009-01-19 7:28 ` Peter Rabbitson
2009-01-26 19:06 ` Bill Davidsen
2009-01-19 7:30 ` Michal Soltys
2009-01-19 12:17 ` Keld Jørn Simonsen
2009-01-19 12:24 ` Peter Rabbitson [this message]
2009-01-19 13:59 ` Keld Jørn Simonsen
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