That's good news! I am backup crazy too. The My Book II is also RAID 1 and recently I replaced one of the drives with a new one. The extra darn near up to date drive is sitting in a secure location.
Transfer of Library to a back-up External HD
My iTunes library (about 500 gigs) is loaded on a Raid-1 Cavalry external HD. In an attempt to get additional back-up I purchased a new FreeAgent Desk 1 TB external HD. The Mac recognizes both HDs, however when I attempt to click and drag from the Cavalry to the FreeAgent the response on the monitor is, in so many words, the transfer can not be completed because the FreeAgent cannot be modified. This was supposed to be super simple according to the Geek at Best Buy. Am I doing something wrong here? The Cavalry is connected to the Mac via Firewire, the FreeAgent is connected via USB.