Media libraries grow large, and hard drives can seem to shrink, as you add thousands of songs and hundreds of videos to iTunes. You may, in fact, think about using a big external drive for iTunes storage (and more iPad videos). That’s just dandy, but you need to make sure that iTunes knows what you intend to do.

If you rudely drag your iTunes Music (or Media) folder to a different place without telling iTunes, it thinks the songs and videos in your collection are gone. The next time you start the program, you’ll find a newly created, empty Music folder. (While iTunes remains empty but calm, you may be having heart palpitations as you picture your media collection vanishing in a puff of bytes.)