If you already got RAID redundancy, why not just create a separate partition in your existing drive(s) and store your backups there?
Well there's your problem! Getting ConfigServer to harden your server!
Just kidding ...
Actually, although technically competition Chirpy is one of the very few people outside myself who I would have confidence in enough to harden a server at least half adequately and coming from me, that is very high praise indeed.
Actually my real point of commenting on the above quote is to mention that The Planet also offers NAS backups (network backup setup to operate as a mounted partition on your server) and I know this first hand as several of my clients are using that service from them.