hi, i use time machine on an OLD usb external for backing up my macbook. I want to buy a new external for backing up now. Does time machine only work with USB external?? ALot of people say to use carbon copy cloner which only works on firewire external. So shall i jsut buy a 1TB external which has USB and Firewire connections? (my mac drive is 250gb....but i will buy a new bigger internal soon 300to500gb probably) thanks.