An analogy for teaching, useful primarily for those over about 30 or so. Feel free to borrow.
The subject is RAID, backups, and off-site backups.
Let’s start with RAID. You’ve seen carbonless copies, where you write on one page and it immediately comes through on the page below. Every mark you make goes there. RAID works like magic carbonless copies for your hard drive. It’s magic because it doesn’t have to be touching. In fact that’s part of why it’s so useful. Since it isn’t touching, the coffee you spill on the original won’t touch the copy.
Now, backups are more like copy machines and faxes. You actually have to take what you’ve got and do the copying and sending. If you make a change on the original it’s not going to be on the copy — you need another copy to get the changes.
Why faxes and copy machines? Well, faxes are when you’re saving at a remote location, and copy machines are when you’re saving where you are. You can save it in the same file cabinet (same drive), or you can put it in another file cabinet (different drive) which can be next to the other or separated (external drive). The fax is for when you’re using what’s called off-site. There are a lot of ways to do that, but for the analogy all you need to know is that it’s easier to fax than to drive over or mail the copy.
As with most analogies it’ll break if carried too far. But to comprehend what’s going on, it works well. Feel free to use when you’re trying to explain it to someone who need to understand.