Re: AW: Locking md device and system for several seconds

[Philippe Pegon <Philippe.Pegon@crc.u-strasbg.fr>]

Miro Dietiker, MD Systems wrote:
> :-)
> 
> 
>>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..

you can use the kernel argument elevator=cfq in your lilo or grub boot 
config file.

you can read this article about cfq :

http://lwn.net/Articles/143474/

for information, it seems cfq is used in the default kernel in some 
distributions.

> 
> I also need to check this on the other (identical) machines.
> 
> Thanks! Miro Dietiker

--
Philippe Pegon