On Tue, May 01, 2012 at 08:18:54PM +1000, NeilBrown wrote:

To replicate:

 - create an array.
 - stop the array
 - assemble the array with at least one missing device e.g.:
    mdadm -A /dev/md0 /dev/sda1 /dev/sdb1
   if it was a 3-device array
 - check in /proc/mdstat that it is listed as "inactivate"
 - reboot
 - now "mdadm -E" the devices.  If the raid level is -unknown- then the bug
   has hit.

Thank you for this info.

After reboot the array came up as active again, and mdadm -E showed "Raid
Level : raid6" for all drives, so that's not the problem I had before.

Regards,

Brian.