At home, I keep all my important stuff on an external hard drive as well as a flash drive.

At work, I am the network admin and all my 12 servers' OS drives are mirrored, and all data drives are running RAID5. I also have 2 backup servers in different locations for backups of my backups. All servers are running on their own UPS. If a hard drive or UPS battery fails, I get an email from the offending device and can generally fix it without having to power down.