One of my WD WDP drives died and the only option seemed to be was to replace the PWB which is $40.00 online. So I have two new 1TB WD Black drives and I tried them and they worked, it seems unlike true raid where the drive are different sizes the smaller size of the two is accessible so mixing a 500g with a 1tb result in a software error. Since 2tb drives are similarly price I will try two 2tb drive to see if they will work; Im not sold on having to use WD brand as well since someone claimed they use a Toshiba in a WD device. Once the price drop on the 2tbs I will look into testing the theory.
We don’t recommend using larger drives or different models to replace the internal drives from a My Book World, since this could make your drive unusable.