When using Time Machine, do you need an empty hard drive (brand new) in order to back-up your mac?
I tried using my hubby's 3TB HD (which already has stuff on it) but it asks me to erase the data on it and when I hit no, nothing happens. I want to back my stuff up in case something happens but not really sure how the external hard drive works with TM. Thanks!
MacBook Pro, OS X Mountain Lion