mdadm failed to autocreate md /dev entries

[m0sia]

I've just upgraded from 10.11 to 11.04

I have the following mdadm.conf(worked like a charm for 10.11):

DEVICE partitions

CREATE owner=root group=disk mode=0660 auto=yes

HOMEHOST <system>

MAILADDR root

ARRAY /dev/md0 level=raid1 num-devices=2 UUID=78bab575:75f15162:d7535677:b830ce1f

After upgrade i have the following mdstat:

$ cat /proc/mdstat
Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10]
md0 : inactive md127p1[0](S)
      488383936 blocks

md127 : active (auto-read-only) raid1 sdc[1] sdb[0]
      488386496 blocks [2/2] [UU]
       resync=PENDING

unused devices: <none>

Two get my raid1 up and running i have to do the following:

 $sudo mdadm --stop /dev/md0
 $sudo mdadm --stop /dev/md127
 $sudo mdadm --assemble /dev/md0 /dev/sdb1 /dev/sdc1
 $sudo mount /dev/md0 /mnt/raid

cat /proc/mdstat
Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10]
md0 : active raid1 sdb1[0] sdc1[1]
      488383936 blocks [2/2] [UU]

unused devices: <none>

$ sudo mdadm --detail --scan --verbose
ARRAY /dev/md0 level=raid1 num-devices=2 metadata=0.90 UUID=78bab575:75f15162:d7535677:b830ce1f
   devices=/dev/sdb1,/dev/sdc1

How can I get mdadm autodetection work as expected?

Best regards,
Dmitry

[m0sia (m0sia)]

It seems i found the root cause of the initial problem: there were a pair of raid superblocks on each hard drive(ex in both /dev/sdb and /dev/sdb1). Until 11.04 it somehow worked for me.

Now i've removed the unnecessary raid superblocks and everything works.
sudo mdadm --zero-superblock /dev/sdb
sudo mdadm --zero-superblock /dev/sdc

But i still wonder if it is a bug or a feature.