Works out fine....they record much like todays new server disaster recovery/nearly continuous backup services to....only the changed bits, not everything. Events makes note from the recordings. So it's efficient in space consumption.
I just went to check to see how much storage is used...but noticed they removed that in newer versions...I can't see a bar of how much of the storage is used. Anyways, with our 8 cams...I have it at 30 days and I don't recall it being very full in the past.