You're right about the 10 hard drives : if you've bought them identically at the same time, it's likely they all gonna fail in a short time span. I've recently heard about the "3,2,1" rule concerning backup :

  - 3 images of your data (1 original + 2 copies).
  - 2 types of media (e.g. extHD and DVD)
  - 1 offshore location (e.g. bank vault, your parents' house,etc.)

Of course it's not a golden rule, but it can prevent catastrophic failures.