So given this one has to ask what that means? My answer is "not much."

But let's be clear here that such is not "backup." It lacks too many items what a backup is.

Backup is:

a. Write protected media.
b. Multiple copies (on and off site.)

Having said that, hard disks in USB and firewire cases are FINE copies but fail as backup systems since they have the same foibles as your internal hard disk.

Bob