Re: Spin down

[NeilBrown <neilb@suse.de>]

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On Mon, 5 Dec 2011 08:49:03 +0100 Vincent Pelletier <plr.vincent@gmail.com>
wrote:

> On Mon, Dec 5, 2011 at 7:11 AM, NeilBrown <neilb@suse.de> wrote:
> > 5 seconds suggests a bitmap update.  Do you have an internal bitmap?
> 
> I don't, but I enabled it on those arrays before with default delay.
> I then removed it when I suspected (with help of block_dump) it to
> cause spin-ups, and I noticed an improvement. Recently, the machine
> was restarted (once on 3.0 kernel, and again to update to 3.1), and
> after both restarts those 5s periodic writes occurred.
> 
> > Then try adding it back with a longer delay
> >  mdadm --grow /dev/md0 --bitmap=internal --delay=60
> 
> Adding bitmaps on both arrays (md0 and md1), 5s periodic writes disappear.
> Removing bitmaps seems to preserve the improvement.
> 
> Could the delay setting have survived on-disk and be used when
> initializing the array, but cleared when mdadm later disables bitmap
> usage ?
> 
> > What kernel version are you running?
> 
> 3.1.4, according to dpkg:
> ii  linux-image-3.1.0-1-amd64                   3.1.4-1
>                      Linux 3.1 for 64-bit PCs
> 
> Regards,


Hmm... I cannot reproduce this which makes it harder.

Can you enable dynamic debugging on md?
Make sure CONFIG_DYNAMIC_DEBUG is set, mount debugfs on /sys/kernel/debug and

 echo module md_mod +p > /sys/kernel/debug/dynamic_debug/control

then look for extra messages in the kernel logs, starting "md:" most likely.

You'll almost certainly see something like

[ 1851.559629] md: waking up MD thread md0_raid1.
[ 1851.625819] md: updating md0 RAID superblock on device (in sync 1)
[ 1851.656878] md: (write) sdb's sb offset: 8
[ 1851.656915] md: (write) sda's sb offset: 8


every 5 seconds.  If you could confirm that and report if there is anything
else reported that might help.

NeilBrown

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