Parallel NFS (pNFS) extends Network File Sharing version 4 (NFSv4) to allow clients to directly access file data on the storage used by the NFSv4 server. This ability to bypass the server for data access can increase both performance and parallelism@ but requires additional client functionality for data access@ some of which is dependent on the class of storage used. The main pNFS operations document specifies storage-class-independent extensions to NFS; this document specifies the additional extensions (primarily data structures) for use of pNFS with block- and volume-based storage.