Hi, I've got the basic 21.5" iMac with the 500GB HDD. I've only got 50GB free so was going to turn my old laptops HDD into an external HDD by putting it in an enclosure. No doubt that it will get full before long as it's only 250GB in size. (I take lots of photos and videos) so I have 2 questions. 1) When my iMacs internal HDD gets full, will the other files I add just spill into the next available HDD? e.g. importing photos into aperture, will it refuse to do it or like I say, spill into the external drive? 2) I was thinking about getting a 3rd external HDD of quite a large capacity (probably 2 or 3TB) and using time machine to back up all of the external drives I add on as and when I need them. Is it possible to backup data onto one drive that is stored on multiple drives?