On Sat, Apr 28, 2012 at 08:03:55AM +1000, NeilBrown wrote:

I'm afraid you've been bitten by a rather nasty bug which is present in 3.3
and got back ported to some -stable kernel.  The fix has been submitted and
should be appearing in -stable kernels soon (maybe already).

Do you happen to know if this bug was present in ubuntu 11.10, kernel
versions 3.0.0-15-server or 3.0.0-16-server ?

I saw failures to assemble RAID6 arrays after unclean shutdowns on both of
these, just in test environments.  If it happens again I'll send mdadm
--examine output. I just tried to replicate it and failed :-(

Regards,

Brian.