Re: mdadm error - superfluous RAID member

[Tom H <tomh0665@gmail.com>]

On Wed, Jun 13, 2012 at 12:40 PM, Christofer C. Bell
<christofer.c.bell@gmail.com> wrote:
> On Wed, Jun 13, 2012 at 3:47 AM, Steve Dowe <sd@warpuniversal.co.uk> wrote:
>>
>> I'm trying to re-use an older server, installing squeeze (6.0.5).  I'm using
>> software RAID and LVM on the machine (details below).  But I must be doing
>> something wrong with the disk set up stage in the installer, as when it
>> boots I see an error flash up quickly:
>>
>>  error: superfluous RAID member (5 found)
>>
>> It appears that the initramfs then gets loaded, the RAID detection fails and
>> it then looks for the LVM volume group, which it can't find (as the LVM
>> group exists on the RAID device).
>
> I don't believe you can boot from a striped volume (raid5 being a
> stripe + parity).  I found some instructions that may allow this to
> work but requires packing a non-standard initrd:
>
> http://nil-techno.blogspot.com/2009/02/booting-fakeraid-raid5-linux-half-assed.html

grub2 can handle "/boot" on mdraid raid5 (and possibly dmraid raid5 too).

>From a raid5 VM:

[root]# grep md0 /proc/mdstat
md0 : active raid5 sdc1[2] sdb1[1] sda1[0]
[root]#
[root]#
[root]# mount | egrep -v 'udev|sys|run|pts|proc'
/dev/md0 on / type ext4 (rw)
[root]#
[root]#
[root]# cat /etc/fstab
UUID=4b202d73-d5e4-4678-916c-6220eddb1b60 / ext4 defaults 0 1
[root]#
[root]#
[root]# grub-probe -t drive /
(mduuid/53da4b0e979e6faa68401fe357f506a3)
[root]#
[root]#
[root]# grub-probe -t drive /boot
(mduuid/53da4b0e979e6faa68401fe357f506a3)
[root]#