mdadm RAID problem -- won't boot

[Tom H]

On Mon, Aug 20, 2012 at 1:36 PM, Rick Bragg <rbragg at gmnet.net> wrote:
>
> I am having a problem booting my system.  My boot disk is not a raid array,
> however, I do have 4 other disks making a raid 10 array that I mount at /mnt/md0.
> My problem is that when I boot my system, I get to a point where it says it
> it can't start the degraded array, and asks me if I want to start the degraded
> array.  If I say yes or no, it always drops me to a shell.  At the shell, I do a
> "cat /proc/mdadm" and I can see 2 arrays!  One is /dev/md0 started, degraded with
> only 3 of my disks (sda1, sdc1, sdd1.)  The other array is /dev/md127 with the
> other disk all by itself (sdb1) and not started.  Again, I am booting from a
> different disk entirely (sde1.)  I tried to remove the md127 array altogether, and
> re-add sdb1 into the md0 array, and it syncs up fine.  After syncing and seeing
> that the md0 array is fine, I reboot.  After rebooting, I get the same problem over
> and over again.
> My question is:
> How can I fix this so that I only have one array at /dev/md0 with all 4 disks
> synced?  Also, how can I bypass this and boot my system without any raid at all so
> I can fix that later?  I am using ubuntu server 10.04 LTS.

The use of md127 usually means that the array's recognized as a
foreign array. Does "mdadm --examine" on sda1 and sdb1 return the same
"local to host" value on the "Name" line?

Did you zero the superblock before re-adding sdb1?