AW: Locking md device and system for several seconds

["Miro Dietiker, MD Systems" <info@md-systems.ch>]

:-)

>Can you check which IO scheduler the drives are using, try different
>schedulers, and see if it makes a different.

there was [anticipatory] selected.

ORIGINAL:
tiger:~#  grep . /sys/block/*/queue/scheduler
/sys/block/fd0/queue/scheduler:noop [anticipatory] deadline cfq
/sys/block/hdd/queue/scheduler:noop [anticipatory] deadline cfq
/sys/block/sda/queue/scheduler:noop [anticipatory] deadline cfq
/sys/block/sdb/queue/scheduler:noop [anticipatory] deadline cfq

NEW:
tiger:~#  grep . /sys/block/*/queue/scheduler
/sys/block/fd0/queue/scheduler:noop anticipatory deadline [cfq]
/sys/block/hdd/queue/scheduler:noop anticipatory deadline [cfq]
/sys/block/sda/queue/scheduler:noop anticipatory deadline [cfq]
/sys/block/sdb/queue/scheduler:noop anticipatory deadline [cfq]

System seems to work, but I need some testing time to check that
behaviour. (Any suggestion of a testing tool to generate disk
traffic and reporting response-times and throughput?)

Which is the right way / position on bootup to set this field
permanent to this value and what exactly did I change with this
modification? (Performance issues?)
I'm using debian..

I also need to check this on the other (identical) machines.

Thanks! Miro Dietiker

-----Ursprüngliche Nachricht-----
Von: Neil Brown [mailto:neilb@suse.de] 
Gesendet: Sonntag, 13. November 2005 11:41
An: Miro Dietiker, MD Systems
Cc: linux-kernel@vger.kernel.org
Betreff: Re: Locking md device and system for several seconds

On Sunday November 13, info@md-systems.ch wrote:
> Hi!
> 
> I'm using kernel 2.6.14.2 with md (RAID1 static) as bootable.
> 
> While md synching (initial creation or after marked one as failed,
> removed and re-added) there are some locking problems with the
> complete system/kernel.

Can you check which IO scheduler the drives are using, try different
schedulers, and see if it makes a different.

     grep . /sys/block/*/queue/scheduler

will show you (the one in [brackets] is active). 
Then just echo a new value out to each file.

I've had one report that [anticipatory] causes this problem and [cfq]
removes it.  Could you confirm that?

Thanks,

NeilBrown