That said, it reduces risk of loss when an actual full backup solution is impractical... I have about 10TB of media on my current 12tb (4x4 raid5) nas box. My next plan is a 6-drive raid z2 with 8-12tb drives early next year. I can't justify doubling the cost or more to ensure it's all backed up. The important bits (to me) are in various redundant places... that doesn't mean I want to lose it and the parity options allow for some safety without too much lose of storage space.