You could do that, but doesn't it seem easier to: 1) initialize a CSPRNG to a known seed; 2) generate random numbers and write them sequentially; 3) initialize a new RNG to the same seed and compare numbers you generate to numbers you read from the storage? That way, you even get to point at the exact byte where the first divergence happens, which might let you say, "this drive which claims to be 30TB seems to be 1GB".