Mdadm

minor number

if something messes up because the mdadm (suddenly) changed
minor number of my md-devices make a backup of your data and follow these steps...
why this changed suddenly ... i have no idea.
i created it using md0, md1, a.s.o.
my system began to throw write-errors, while running...
after reboot it didn't come up again...

# mdadm --detail /dev/md127

/dev/md127:
        Version : 0.90
  Creation Time : Wed Sep 14 10:14:13 2011
     Raid Level : raid1
     Array Size : 475788992 (453.75 GiB 487.21 GB)
  Used Dev Size : 475788992 (453.75 GiB 487.21 GB)
   Raid Devices : 2
  Total Devices : 2
Preferred Minor : 127
    Persistence : Superblock is persistent
[...]

shows you the preferred minor: 127 (which is stored in the superblock)

mdadm --stop /dev/md127
mdadm --assemble --update=super-minor /dev/md1 /dev/sdb8 /dev/sda8 

tell your initrd about the new setting:

update-initramfs -u