dhicks: dont get me wrong, I love your model and it would certainly be one of the option I would consider, but it isnt something you can plough into without being confortable with the concept and the workings of it. rsync is capible of duplicating block devices now isnt it? I assume this is what you are talking about? Or are you referring to file level with LVM taking a snapshot, rsync mirroring it off, and then deleting the snapshot?
Either way its not masively complicated but IME it is way above alot of peoples heads and is certainly not something our LEA would be happy with for the reasons localzuk has mentioned.
Localzuk: you are certainly heading down the right path as far as your requirements. You do need to consider my point on how your fileserver will work. Does the Overland handle this well? Also how does the Overland handle HA? It seems that good HA is one of the big things you pay for with the expensive SANs. Dont just assume that you can buy a Overland and then the QNAP for a backup SAN as depending on the protocols used this may not be possible.