[Brutus2600]

As others have said, but redundancy is the name of the game.

For my personal backup, I have everything on the computer I'm using. Then every month or two I make a backup on an external drive. I also have ANOTHER identical external drive that I copy that drive onto.

I haven't done this yet, but ideally you would take that second external drive and put it somewhere else. Say at your parents house, at work (if it's secure), or a bank lock box. That way if your house ever burned down you still have all your data backed up.

Yes, it's inconvenient, but it will reduce your risk of losing your data to a very very small percentage.

You should also consider the media you're using to backup your data.

CD/DVD's can go bad, but if you keep them out of sunlight, heat, and keep them unscratched, they'll last a long time.

Hard drives can last anywhere from one week after you bought them to years and years. I've had hard drives die within a month of buying them and others that have worked for close to a decade. Consider them disposable items though, and that they will need to be replaced every couple years and never rely on just one copy.

Solid state media (SSD hard drives or thumb drives) don't have any moving or mechanical parts like regular hard drives do and can't be scratched like CD/DVD's can, but these can still get corrupted. Thumb drives are so large and have come down in price so much now days that if you have a small enough amount of data (<64gigs of data) it's quite easy to make a couple of quick copies of your data on these and have a quick and convenient backup available.