If you only have one location but a decent link to the net then Scott's answer is the way to go. Do it during off hours. Use one of the cloud backup services. Carbonite and Mozy come to mind first for a small business. Simple, reliable and reasonably inexpensive. A hard drive attached to a computer that you swap out and carry around is a bad idea for many reasons. You will forget, you will drop it or some crack head will steal it out of your car when you stop for beer on the way home. As for frequency, weekly is also a bad idea. If you need this backup, it is going to be because something really bad happened. You don't want to add to that by having to say "It's going to take a week to rebuild our network and then we will also lose a weeks worth of data, so ummm yea this is basically a two week loss for the company'. That would be a resume generating event, as it should be. Neither Mac Automator or Time Machine are acceptable for this job. If you go cloud you will get software from them for this. If you have multiple locations speak up, then my answer changes.