Bug#784070: mdadm Software RAID1 with GPT on Debian 8.0.0 amd64 - Does not mount/boot on disk removal

[Pascal Hambourg]

I can reproduce the problem, which did not happen with Wheezy.
UEFI boot, fresh Debian 8 amd64, RAID 1 on two GPT disks.

Another person experienced it too on disks with legacy MBR/MSDOS
partition scheme, so I do not think it is related to GPT.

Note that this does not happen when the missing member was previously
recorded as faulty.

The problem seems to be caused by the incremental assembly performed by
udev in /lib/udev/rules.d/64-md-raid-assembly.rules. When a member is
missing, it leaves the array in an "inactive" state. The classic
assembly performed in the mdadm initramfs script
(/usr/share/initramfs-tools/scripts/local-top/mdadm) does not activate
it, probably because the array already exists.

Should the mdadm script force activation of required degraded arrays
with mdadm --run ?