29.7 NFS Version 3

During 1993 the specifications for version 3 of the NFS protocol were released [Sun Microsystems 1994]. Implementations are expected to become available during 1994.

Here we summarize the major differences between versions 2 and 3. We'll refer to the two as V2 and V3.

The file handle in V2 is a fixed- size array of 32 bytes. With V3 it becomes a variable-length array of up to 64 bytes. A variable-length array in XDR is encoded with a 4-byte count, followed by the actual bytes. This reduces the size of the file handle on implementations such as Unix that only need about 12 bytes, but allows non-Unix implementations to maintain additional information.
V2 limits the number of bytes per READ or WRITE RPC to 8192 bytes. This limit is removed in V3, meaning an implementation over UDP is limited only by the IP datagram size (65535 bytes). This allows larger read and write packets on faster networks.
File sizes and the starting byte offsets for the READ and WRITE procedures are extended from 32 to 64 bits, allowing larger file sizes.
A file's attributes are returned on every call that affects the attributes. This reduces the number of GETATTR calls required by the client.
WRITEs can be asynchronous, instead of the synchronous WRITEs required by V2. This can improve WRITE performance.
One procedure was deleted (STATFS) and seven were added: ACCESS (check file access permissions), MKNOD (create a Unix special file), READDIRPLUS (returns names of files in a directory along with their attributes), FSINFO (returns the static information about a filesystem), FSSTAT (returns the dynamic information about a filesystem), PATHCONF (returns the POSIX.1 information about a file), and COMMIT (commit previous asynchronous writes to stable storage).