A single backup is NOT good enough.
When I was about 8 years old I accidently overwrote this huge game I was programming on my Tandy. I was smart enough to have a backup, but on that particular day I decided to overwrite it with my newest program code.
Stupid me didn't realize that the newest update was broken!
Yeap, I just overwrote my backup with a bad copy . . .
But I was a pretty smart 8 year old . . . I had a secondary backup! bite you, Murphy
! hehe. Unfortunately, that secondary backup was a month old and missing tons of code . . .
However a secondary backup still isn't good enough . . . I lived in louisiana and there was a flood in '93 that destroyed a lot of my stuff. So to my next point . . . put your backups OUTSIDE your home and in another location. A bank safety deposit box, your work office, a friends house, etc.
What if your house has a fire and your computer and everything in the house is destroyed? Exactly.
Backups I have for SoR:
my external harddrive
an off site cd in my office
And for my robot code, I even backup older versions of my code, dated and all . . . just in case . . . and its saved me several times too.