Good post by George Crump (thank you)
Short of buying a new storage system with storage efficiency (deduplication and compression) built in, it is difficult to add the technology to an existing storage array. Today there are two ways to accomplish this. First, you can wait for your storage vendor to add the capability and hope it is backward compatible. Second, you can add a software defined storage layer to replace your current storage software, but leverage your existing storage hardware. Now there is a third option, retroactive deduplication, which adds storage efficiency to the existing storage hardware but does not replace its software.
Read on here