"a bit by bit comparison if the hash matches, and store the blocks separately if it they are different."
Surely doing that (and the other unmentioned but essential bits) isn't a sign of paranoia, it's a sign that doing otherwise is stupid?
A storage system that returns some largely unexpected data with no relationship to the original except it has the same hash isn't really much of a storage system, in my book. But then maybe I'm a dinosaur. Dinosaurs are extinct. Marketing people and their equivalents on the purchasing side (techno-hipsters?) are still with us.