A system and method for mapping file block numbers (FBNs) to logical block addresses (LBAs) is provided. The system and method performs the mapping of FBNs to LBAs in a file system layer of a storage operating system, thereby enabling the use of clients in a storage environment that have not been modified to incorporate mapping tables. As a result, a client may send data access requests to the storage system utilizing FBNs and have the storage system perform the appropriate mapping to LBAs.