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Re: XFS blocked task in xlog_cil_force_lsn

To: xfs@xxxxxxxxxxx, xfs@xxxxxxxxxxx
Subject: Re: XFS blocked task in xlog_cil_force_lsn
From: Arkadiusz MiÅkiewicz <arekm@xxxxxxxx>
Date: Fri, 20 Dec 2013 23:43:47 +0100
Cc: stan@xxxxxxxxxxxxxxxxx, linux-raid@xxxxxxxxxxxxxxx
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On Friday 20 of December 2013, Kevin Richter wrote:

> >> $ cat /sys/block/md2/md/stripe_cache_size
> >> 256
> > 
> > 256 is the default and it is way too low.  This is limiting your write
> > througput.  Increase this to a minimum of 1024 which will give you a
> > 20MB stripe cache buffer.  This should become active immediately.  Add
> > it to a startup script to make it permanent.

> > $ echo 256 > /sys/block/md2/md/stripe_cache_size
> > $ time cp -a /olddisk/testfolder /6tb/foo1/
> > real    25m38.925s
> > user    0m0.595s
> > sys     1m23.182s
> > 
> > $ echo 1024 > /sys/block/md2/md/stripe_cache_size
> > $ time cp -a /olddisk/testfolder /raid/foo2/
> > real    7m32.824s
> > user    0m0.438s
> > sys     1m6.759s
> > 
> > $ echo 2048 > /sys/block/md2/md/stripe_cache_size
> > $ time cp -a /olddisk/testfolder /raid/foo3/
> > real    5m32.847s
> > user    0m0.418s
> > sys     1m5.671s
> > 
> > $ echo 4096 > /sys/block/md2/md/stripe_cache_size
> > $ time cp -a /olddisk/testfolder /raid/foo4/
> > real    5m54.554s
> > user    0m0.437s
> > sys     1m6.268s
> 
> The difference is really amazing! So 2048 seems to be the best choice.
> 60GB in 5,5minutes are 180MB/sek. That sounds a bit high, doesnt it?
> The RAID only consist of 5 SATA disks with 7200rpm.

I wonder why kernel is giving defaults that everyone repeatly recommends to 
change/increase? Has anyone tried to bugreport that for stripe_cache_size 
case?

-- 
Arkadiusz MiÅkiewicz, arekm / maven.pl

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