Hello everyone, I have a 2011 13' Macbook Air (with 128gb flash storage). I also have a 500gb external hard drive, which is the size of a brick. I would like to backup all of my files on my laptop onto an external hard drive using the time machine application. Though I would also like this external hard drive to be extra storage. So part back-up, part extra storage (as I have over 150gb of other files that don't fit on my mac). I'm thinking for a new hard drive it will need to be 1gb minimum, I would like one that doesn't need its own power supply. I guess it would plug into the existing USB2.0, I don't know if I could use the thunderbolt to transfer faster. Would anyone be able to help me here? Thank you. Cheers, Chris P.S. Are these drives and time machine able to backup my dropbox folder. I currently use dropbox to back up all my PhD files.