... just be sure to set up a RAID (redundant array of independent disks), I'd say a RAID-1, but there are better arrangements.
It'll cost more because the point is: making a duplicate of everything you write to disk. So, if you need 1TB of space, you'll need 2TB of disk space ... everything you backup will be written twice. If one disk fails, you can still recover from the other(s).
All enterprise backup systems use RAID.
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Fuck 'em all, we don't need 'em