Herman,
While the likelyhood of hard drive failures is slim, it can and does happen, and at the worst time... and can and does happen to backups as well.
I will tell you of the time I screwed up restoring from a back up drive and ruined both of them.... unfortunately it was at my fathers store while he was in the hospital so I basically lived there reentering all the data I screwed up.....
Yes, this ws caused by my stupidity, but I am not a dumb man... at least I don't think so, but the moral is you never have enough backup. I have all my and my wifes cd's on a HD, and I have elected to throw out all the jewel cases and store them in large CD books, they only take up a shelf in the closet and are always there should I need them.
Just my 0.02.