I bought an IOMega 2T USB 3.0 ext drive to do a backup. Got SuperDuper! and a few hours later I have a backup. I've looked at the files and all seems to be intact. I did my OS upgrade SL 10.6.8 So that I can now buy ML for the next upgrade. I wanted a HDD backup that I can boot to whenever I want/need to. How to I make the USB drive bootable? I see nothing in Disk Utilities or in SuperDuper!