[don-o]

Use a "ghost" program and a USB drive. I won't suggest a program because that would start an argument, but google the terms "ghost backup" and you'll find what you need. I use a 400gb USB drive and partition it for 3 different OSes.

I have two internal HD's already. Will that work if I reformat the slaves?

[Glenn]

have two internal HD's already.

A USB drive is external and plugs into your USB port. Handy for multiple computers. I couldn't live without it.

[Fresh Wind]

You want your backup drive to be physically and electrically separate from your computer. Depending on how critical your data is, you might want to store it in a fire safe or in another building.

[DB]

The reason to use an external USB or Firewire drive for backup is that if you get a virus or other destructive program, it can wipe out data on all the hard drives currently running on your computer - back ups and all.

Because the backup device is off line normally (disconnected or powered down) it is unaffected and can be used to recover everything regardless of what happened.

Another reason is that since it is normally not powered up it is much less likely to fail and therefore more likely to be around when you need it.