My music collection sits on a server hooked up to my stereo. I had the disks in RAID-Z1, but when one of the disks pulled a Seagate I accidentally made the disks striped vedvs. To back this up, I boot up a rackmount server with larger disks in RAID-Z1 and use rsync.
This is the only data that I really care about preserving. I found this out through changing my operating system a lot and having my laptop stolen.