From: NeilBrown <neilb@suse.de>
To: Bart Kus <me@bartk.us>
Cc: linux-raid@vger.kernel.org
Subject: Re: Increasing maxsect of md devices?
Date: Thu, 3 Mar 2011 09:59:29 +1100 [thread overview]
Message-ID: <20110303095929.25b800da@notabene.brown> (raw)
In-Reply-To: <4D6EC3FA.4030809@bartk.us>
On Wed, 02 Mar 2011 14:26:02 -0800 Bart Kus <me@bartk.us> wrote:
> Hello,
>
> This seems contradictory:
>
> jo ~ # blockdev --getiomin /dev/md5
> 524288
> jo ~ # blockdev --getioopt /dev/md5
> 4194304
> jo ~ # blockdev --getmaxsect /dev/md5
> 255
> jo ~ # blockdev --getbsz /dev/md5
> 4096
> jo ~ # blockdev --getss /dev/md5
> 512
> jo ~ #
>
> Optimal IO size is reported as 4MB (and that is indeed the stripe size),
> but maximum sectors per request is only 128kB? How can software do
> optimal 4MB IOs with the maxsect limit? Does XFS care about this limit?
md/raid doesn't use 'requests' the any maximum is meaningless.
raid4/5/6 does have a 'stripe cache' which is a vaguely similar thing. There
can sometimes be value in changing that.
The devices that the array are built from may have a 'maximum sectors per
request', but that probably isn't particularly related to chunk size.
BTW, where do you find "maximum sectors per request in only 128kB" in the
details you quoted - I don't see it.
NeilBrown
next prev parent reply other threads:[~2011-03-02 22:59 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-03-02 22:26 Increasing maxsect of md devices? Bart Kus
2011-03-02 22:59 ` NeilBrown [this message]
2011-03-03 0:45 ` Bart Kus
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