The past few days have been where I realize that my solution for maximum data redundancy has failed to address maximum functional redundancy though. I think it's something I'll *have* to address for book 3... not sure how, though. I'll need to talk to an engineer friend of mine. Probably two servers that act like one virtual machine, where if one drops out, the other carries on... or something.
Don't. Mechanical parts break, and hard drives are 100% mechanical. Using two hard drives actually doubles the chance of a failure. And if one drive goes, there's a fair chance it'll take the rest of the system with it.
Use a flash drive; they're solid state and have no moving parts. Then find a cloud solution like Google Drive and let them manage the redundant hard drive solution. Work-system + flash drive + cloud = reasonably secure backup solution.