I have two external harddrives with all my data on it, my new desktop? HAS NOTHING.
What I do is simply unplug the drives if I am not using them, I have enough music on my desktop it gets me through.
I could throw the PC out the window, and wouldn't care, everything is safe. What happens if one drive goes bad? I replace it before turning on the other drive.
I did have one External book with just 1 backup copy of my stuff, fall off a desk and click, LOSS of everything - this is why I keep TWO copies, I paid $90 for pair of 750gb drives, they are not networked, as they are esata/USB (insurance in case a problem with 1 or other).
Ever since I started doing this back in 2000 I never had a problem, I did have one drive fail (early version of western digital black) otherwise its not worth taking the risk