No YOU fail!

I trust you're not an IT prof. Duplicating disks (preferably at a remote site) is straightforward and great for disaster recovery (providing you think a disaster can't affect both sites simultaneously), but it can't handle the "Oh dear, I accidentally deleted my directory. I'm not sure when, but it was definitely there a month ago" problem (unless you're prepared to increase your total disk space by a factor of 20x or so). And off-siting hard disks is a pain compared to tape.

I confidently predict tape will be around for a long time yet.