Sigh. Windows managed to kill my RAID already. I sent it to hibernate, brought it back and it booted half-way before resetting itself. Two disks in a mirrored pair had now vanished from the array, rendering it dead. Much reconnecting of disks was performed in the vain hope that it was a spontaneous connection fault, but it seems not. This is worryingly similar to the Windows 2000 bug that Orac suffered from, whereby Windows cheerily turned off the power before the disks had time to flush their write-caches.
Happy New Year, everybody!