Amazon EBS claims five nines. I'm not sure how you convert AFR to uptime (you can't, I think is the quick answer), but it's interesting to think about how long it takes to come back from a busted drive. And 4% seems low. Guess that's if they're in striped RAIDs and rotated out pretty regularly.

I've got giant folders called "AppsToInstall", one in DropBox (Mac) and in OneDrive (Windows) that makes it a lot quicker to go from hd death to coding, and most of my stuff is in some git repo in the cloud somewhere, but it's still more time than I should spend. Backups for home boxen are under-utilized.