Configured Studio II and it erased other HDD!

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!

YIKES.

I ejected, reconnected.  No change.  Still renamed, still empty.

Restarted.  No change.  Still renamed, still empty.

Any suggestions?

Try a data recover software. Disk Warrior is powerful but is not free.