I just received my 2TB My Book Studio Pro II and installed the software.
I opened the WD Manager and told it configure the two 1TB drives to a RAID 1 (mirrored).
In the middle of that process I connected a second external HDD (that contained my iTunes, etc).
The mounting icon for my 2nd HDD appeared, then disappeared briefly, and reappeared, renamed and EMPTY!
I ejected, reconnected. No change. Still renamed, still empty.
Restarted. No change. Still renamed, still empty.