Recovering nested raid (was LSI MegaRAID SAS 9240-4i hangs system at boot)

[Ramon Hofer <ramonhofer@bluewin.ch>]

On Mon, 18 Jun 2012 00:46:55 +0200
Ramon Hofer <ramonhofer@bluewin.ch> wrote:

> I'm again having problems with the disks getting kicked out of the
> array :-o

I've already asked this before on the debian list and got an answer.
But I'm not sure if I should do this.

Here's a link to my old problem:
http://lists.debian.org/debian-user/2012/04/msg01290.html

The answer from Daniel Koch (thx again) was:

> - Zero all the superblocks on all the disks.
> ~$ mdadm --zero-superblock /dev/sd{b..d}
> 
> - Recreate the array with the "--assume-clean" option.
> ~$ mdadm --create --verbose /dev/md0 --auto=yes --assume-clean
> --level=5 --raid-devices=3 /dev/sdb /dev/sdc /dev/sdd
> 
> - Mark it possibly dirty with:
> ~$ mdadm --assemble /dev/md0 --update=resync"
> 
> - Let it resync
> 
> - Mount it and see if it is restored

I'm not sure if this is the correct way here too because I have a
nested raid.

If yes then this should work for me now:

~$ mdadm --zero-superblock /dev/sd[abcd]
~$ mdadm --zero-superblock /dev/sd[efgh]

~$ mdadm --create --verbose /dev/md1 --auto=yes --assume-clean
--level=5 --raid-devices=4 /dev/sd[abcd]
~$ mdadm --create --verbose /dev/md2 --auto=yes --assume-clean
--level=5 --raid-devices=4 /dev/sd[efgh]

~$ mdadm --assemble /dev/md1 --update=resync
~$ mdadm --assemble /dev/md2 --update=resync

Now md0 should have it's members back and I can start it again
~$ mdadm -A /dev/md0 /dev/md[12]

And if I'm very lucky this time I still have my data on the array :-)


I wanted to ask you before I try this if this could help.
Maybe I should ask in the linux raid mailing list too?


Cheers
Ramon