It's not about any of that. Unless you have a magic tape and tape drive, there is no parity or striping you can do that actually involves tape. Tapes aren't random access devices, but that is what RAID-style parity requires. So either you get as many tape drives as you have tapes, or you copy the contents of all the tapes one by one to on-line storage (not online as in the internet, but on-line as in: directly available). In the first case, that'd be extremely expensive, and in the second case, why not use those drives that hold the same data as the tapes in the first place...