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

I have a RAID60 that I want to expand.

The current setup is: 2 axles each having 9 disks + 2 spares.

The future wanted setup is: 4 axles each having 10 disks + 1 spare.

So I need to do some --grow to reshape the drives.

I thought this would be enough:

  mdadm -v --grow /dev/md1 --raid-devices=10 --backup-file=/root/back-md1
  mdadm -v --grow /dev/md2 --raid-devices=10 --backup-file=/root/back-md2
  mdadm -v --grow /dev/md0 --raid-devices=4 --add /dev/md3 /dev/md4

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

I assume you are getting this error when running a test with small loop-back
devices - yes?
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.

NeilBrown

How can I --grow a RAID6 to use more devices?

Info about the system:

  $ mdadm --version
  mdadm - v3.2.5 - 18th May 2012
  $ uname -r
  3.5.0-17-generic

This URL includes a Makefile to reproduce the problem:
http://serverfault.com/questions/503832/linux-mdadm-grow-raid6-something-wrong-reshape-aborted


/Ole
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