Is RDC true block-level replication?
No. RDC is a general purpose protocol for compressing file transfer. DFS Replication uses RDC on blocks at the file level, not at the disk block level. RDC divides a file into blocks. For each block in a file, it calculates a signature, which is a small number of bytes that can represent the larger block. The set of signatures is transferred from server to client. The client compares the server signatures to its own. The client then requests the server send only the data for signatures that are not already on the client.
