You are speaking of NAS device and I am speaking strictly about some pretty good, low-cost NVR's. You can buy a Hikvision NVR (just for example) and get the software for free. It is purpose-built to store and retrieve video. Sanyo, Samsung and others have good machines too by the way.
Just my opinion only, but to purchase a NAS for the sake of doing it is cutting your nose off to spite your face, respectfully. Don't get so hung up looking at the trees that you miss the forest. Enough metaphors probably.
My point is there are some really good, sound, purpose-built devices that will accomplish what you are looking to accomplish; and they are virtually plug and play. My advice would be more specific if I knew the camera models you want to employ. That makes it easy. I would research the NVR's that are actually tested with your camera models and go from there. I don't think you will save significant dollars, and your headaches could be compounded.
While Razberi is a good device, you would need to purchase an NVR software package with licenses and that is not what you are going for, as I read.