Comment 3 for bug 945786

The disk was /dev/sdc in the first instance because it was plugged after cd-rom took /dev/sdb. In the second instance it was left plugged in on boot, taking /dev/sdb and leaving /dev/sdc for the cd-rom.

Subsequent reboots with both disks plugged in, and removing my mdadm udev override (removed just in case) have had no change on the outcome.