On Friday December 12, jura@xxxxxxxxxx wrote:
> Hello.
>
> I've run into next problem:
>
> there was raid5 md11( 3 of 3) from sdb4,sdg1,sdd1
> i've run
> mdadm /dev/md11 -a /dev/sdc1
> mdadm /dev/md11 -a /dev/sde1
> mdadm /dev/md11 -a /dev/sdf1
> mdadm --grow /dev/md11 --raid-devices=6
> reshape started
> shortly after i realized that sdd1 was too slow , and removed it
> mdadm /dev/md1 -f /dev/sdd1 -r /dev/sdd1
> and rebooted in hope to fix sdd speed
>
> after that md11_reshape stalled and md11 unaccessible
> and programms tried to access md11 stuck in D state too
> also strange to see
> Delta Devices : 2, (4->6)
Why is this strange? You are reshaping an array from 4 drives to 6
devices. The difference (delta) between those numbers is 2. Hence
the message.
>
> Any chance get to complete reshape or receive access to md11 at least read-only?
>
>
>
> Below different outputs that might help to identify problem.
> cat /proc/mdstat
> md11 : active raid5 sdb4[0] sde1[5] sdf1[3] sdg1[2] sdc1[1]
> 586073088 blocks super 0.91 level 5, 1024k chunk, algorithm 2 [6/5] [UUUU_U]
^^^^^
That is a useful clue, together with the stack traces.
To reshape an array, md needs to cache at least 4 full stripes. With
a chunk size of 1024K, that is 1024 4K pages.
The stripe_cache_size defaults to 256 which is too small.
When you start a reshape, mdadm increases the size of the stripe_cache
to whatever you need. However when you assemble the array after
a reboot in the middle of a reshape, mdadm doesn't fix the
stripe_cache_size. I need to fix that.
You can do it by hand with the command
echo 1024 > /sys/block/md11/md/stripe_cache_size
That should cause the reshape to start running smoothly.
Thanks,
NeilBrown
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