A computer has access to a system-formatted data storage unit (DSU) containing a file system and to a raw DSU. A file within the file system constitutes a raw DSU mapping that facilitates access to the raw DSU. The raw DSU mapping appears to be an ordinary file to a storage user, but with the size of the raw DSU. An attempted access to the raw DSU mapping is translated into a corresponding access to the raw DSU. Access to the raw DSU by the storage user may be restricted to a specified region of the raw DSU, by defining an extent within the raw DSU mapping. The raw DSU mapping provides access to the raw DSU with many of the advantages of using a file system, including name persistency, permissions, persistent attributes, locking information for a distributed file system and other extended metadata.