Comment 2 for bug 645575

Instead of applying Adalberto's patch

I found this http://ubuntuforums.org/showthread.php?p=11388915 and it works for me
tl;dr there is a race condition between assemble of the raid array and the check on the health of the array.

In file, /usr/share/initramfs-tools/scripts/mdadm-functions

Modify function from:
degraded_arrays()
{
        mdadm --misc --scan --detail --test >/dev/null 2>&1
        return $((! $?))
}

To:
degraded_arrays()
{
        udevadm settle
        mdadm --misc --scan --detail --test >/dev/null 2>&1
        return $((! $?))
}