On Mon, May 6, 2013 at 8:44 AM, NeilBrown [off-list ref] wrote:

On Thu, 2 May 2013 13:56:09 +0200 Ole Tange [off-list ref] wrote:

:

quoted

I thought this would be enough:

  mdadm -v --grow /dev/md1 --raid-devices=10 --backup-file=/root/back-md1

:

quoted

The last command works, but the 2 first commands fail with:

  mdadm: Need to backup 7168K of critical section..
  mdadm: /dev/md2: Something wrong - reshape aborted

:

Very sensible to test first.  However to reshape a RAID6 from 9 to 10, you
need each device to be at least 7*8*chunksize*2 - possibly a bit more than
that.
Your script uses a chunksize of 128K, so you need at least 15Meg
Your script creates 1Meg devices.

Try your test with a  much smaller chunk size and a somewhat larger device
size.

Spot on. If I adjust the size of the loop-back devices to 30M instead
of 1M, then everything works.


/Ole