Comment # 9 on bug 907738 from Neil Brown

The fact that "_0" is being appended to the name implies that:
1/ the array is not listed in /etc/mdadm.conf, and
2/ the host name stored in the metadata does not match the hostname of the
host.

Can you please report:
1/ mdadm --examine   of one of the component devices
2/ hostname
3/ content of /etc/mdadm.conf
4/ content of /etc/mdadm.conf in the initrd

My guess is that the hostname in the metadata is some sort of generic name, and
that the array is being assembled from the initrd.  If that is the case the
best fix is to make sure the initrd *only* assembles arrays listed in
/etc/mdadm.conf in the initrd.  I thought we did that already but I'm not sure.