Getting md0 to come back automatically

I'm running mdadm 1.9.0 on a Debian build (using coLinux 0.7.1), and
have the following for my /etc/mdadm/mdadm.conf:

ARRAY /dev/md0 level=raid5 num-devices=4
UUID=777b15e6:6791bb61:96a9c2f4:80e2f7bf
DEVICE /dev/cobd3,/dev/cobd4,/dev/cobd5,/dev/cobd6

I can rebuild the array manually after a restart using:

mdadm -A /dev/md0 /dev//cobd3 /dev/cobd4 /dev/cobd5 /dev/cobd6

but it doesn't come up automatically on it's own. Anything that y'all
can see that's wrong with this?

Thanks,
Ewan