Wrapping HASHBYTES with CHECKSUM is not a good idea. CHECKSUM generates a 32 bit hash using a simple bit-shift+XOR algorithm. So it provides very poor uniqueness with the first collision expected at 2^16. HASHBYTES generates 128 or 160 bit hashes. For more uniqueness you can use CLR or SSIS script components/custom components to generate SHA-256, 384 or 512 bit hashes.