linux-kernel - Re: Software RAID (non-preempt) server blocking question. (2.6.20.4)

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Date:	Thu, 29 Mar 2007 05:00:51 -0400 (EDT)
From:	Justin Piszcz <jpiszcz@...idpixels.com>
To:	Henrique de Moraes Holschuh <hmh@....eng.br>
cc:	Neil Brown <neilb@...e.de>, linux-kernel@...r.kernel.org,
	linux-raid@...r.kernel.org
Subject: Re: Software RAID (non-preempt) server blocking question. (2.6.20.4)



On Thu, 29 Mar 2007, Henrique de Moraes Holschuh wrote:

> On Thu, 29 Mar 2007, Justin Piszcz wrote:
>>> Did you look at "cat /proc/mdstat" ?? What sort of speed was the check
>>> running at?
>> Around 44MB/s.
>>
>> I do use the following optimization, perhaps a bad idea if I want other
>> processes to 'stay alive'?
>>
>> echo "Setting minimum resync speed to 200MB/s..."
>> echo "This improves the resync speed from 2.1MB/s to 44MB/s"
>> echo 200000 > /sys/block/md0/md/sync_speed_min
>> echo 200000 > /sys/block/md1/md/sync_speed_min
>> echo 200000 > /sys/block/md2/md/sync_speed_min
>> echo 200000 > /sys/block/md3/md/sync_speed_min
>> echo 200000 > /sys/block/md4/md/sync_speed_min
>
> md RAID1 resync reacts *extremely* badly to CFQ.  Just a data point, you may
> want to check on it.  Might mean other RAID types also get screwed, and also
> that md "check" is also disturbed by CFQ (or disturbs CFQ, whatever).
>
> I reverted everything here to non-CFQ while the RAID did its resync (which
> fixed all issues immediately), and we went back to 2.6.16.x later for other
> reasons.
>
> --
>  "One disk to rule them all, One disk to find them. One disk to bring
>  them all and in the darkness grind them. In the Land of Redmond
>  where the shadows lie." -- The Silicon Valley Tarot
>  Henrique Holschuh
>

I am using the AS scheduler; not CFQ.

$ find /sys 2>/dev/null|grep -i scheduler|xargs -n1 cat
noop [anticipatory]
noop [anticipatory]
noop [anticipatory]
noop [anticipatory]
noop [anticipatory]
noop [anticipatory]
noop [anticipatory]
noop [anticipatory]
noop [anticipatory]
noop [anticipatory]
noop [anticipatory]
noop [anticipatory]

Justin.
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