Ok, I went out and purchased a 1TB My Book, to backup my Macbook Pro and External 750GB My Book. The initial backup was about 58GB. My music collection sits on my external 750GB drive and is about 250GB of music. Time Machine does not appear to be backing it up. Does Time Machine not support backing up external drives or am I doing something wrong? FWIW- I did make sure the external drive was not in the "exclude" list, but its still not working.