Thanks Neil.
Thanks for the extra detail. Everything looks sensible so far.
Can you check the contents of mdadm.conf on the initrd please.
e.g.
cd /tmp
zcat /boot/initrd | cpio -idv
cat etc/mdadm/mdadm.conf
something like that.
NeilBrown
content of /boot/initrd.img-3.2.0-24-generic:
; egrep -v '^#|^$' etc/mdadm/mdadm.conf
CREATE owner=root group=disk mode=0660 auto=yes
HOMEHOST <system>
ARRAY /dev/md/0 metadata=1.2 UUID=4195aaa7:0ebd37ce:d4b9481e:1a68f4a8
name=disc:0