Протокол распределенной файловой системы NFS: история и развитие

Distributed file system protocol

a specific protocol

Network File System (NFS) is a distributed file system protocol originally developed by Sun Microsystems (Sun) in 1984, allowing a user on a client computer to access files over a computer network much like local storage is accessed. NFS, like many other protocols, builds on the Open Network Computing Remote Procedure Call (ONC RPC) system. NFS is an open IETF standard defined in a Request for Comments (RFC), allowing anyone to implement the protocol.

Sun used version 1 only for in house experimental purposes. When the development team added substantial changes to NFS version 1 and released it outside of Sun, they decided to release the new version as v2, so that version interoperation and RPC version fallback could be tested. The Virtual File System interface allows a modular implementation, reflected in a simple protocol. By February 1986, implementations were demonstrated for operating systems such as System V release 2, DOS, and VAX/VMS using Eunice. and attributes along with file names when scanning a directory;
assorted other improvements. The first NFS Version 3 proposal within Sun Microsystems was created not long after the release of NFS Version 2. The principal motivation was an attempt to mitigate the performance issue of the synchronous write operation in NFS Version 2. By July 1992, implementation practice had solved many shortcomings of NFS Version 2, leaving only lack of large file support (64 bit file sizes and offsets) a pressing issue. This became an acute pain point for Digital Equipment Corporation with the introduction of a 64 bit version of Ultrix to support their newly released 64 bit RISC processor, the Alpha 21064. At the time of introduction of Version 3, vendor support for TCP as a transport layer protocol began increasing. While several vendors had already added support for NFS Version 2 with TCP as a transport, Sun Microsystems added support for TCP as a transport for NFS at the same time it added support for Version 3. Using TCP as a transport made using NFS over a WAN more feasible, and allowed the use of larger read and write transfer sizes beyond the 8 KB limit imposed by User Datagram Protocol.

WebNFS was an extension to NFSv2 and NFSv3 allowing it to function behind restrictive firewalls without the complexity of Portmap and MOUNT protocols. WebNFS had a fixed TCP/UDP port number (2049), and instead of requiring the client to contact the MOUNT RPC service to determine the initial filehandle of every filesystem, it introduced the concept of a public filehandle (null for NFSv2, zero length for NFSv3) which could be used as the starting point. Both of those changes have later been incorporated into NFSv4.

Version 4 (RFC 3010, December 2000; revised in RFC 3530, April 2003 and again in RFC 7530, March 2015), influenced by Andrew File System (AFS) and Server Message Block (SMB, also termed CIFS), includes performance improvements, mandates strong security, and introduces a stateful protocol. Version 4 became the first version developed with the Internet Engineering Task Force (IETF) after Sun Microsystems handed over the development of the NFS protocols. NFS version 4.1 (RFC 5661, January 2010; revised in RFC 8881, August 2020) aims to provide protocol support to take advantage of clustered server deployments including the ability to provide scalable parallel access to files distributed among multiple servers (pNFS extension). Version 4.1 includes Session trunking mechanism (Also known as NFS Multipathing) and available in some enterprise solutions as VMware ESXi. NFS version 4.2 (RFC 7862) was published in November 2016 with new features including: server side clone and copy, application I/O advise, sparse files, space reservation, application data block (ADB), labeled NFS with sec label that accommodates any MAC security system, and two new operations for pNFS (LAYOUTERROR and LAYOUTSTATS). One big advantage of NFSv4 over its predecessors is that only one UDP or TCP port, 2049, is used to run the service, which simplifies using the protocol across firewalls.

NFS is often used with Unix operating systems (such as Solaris, AIX, HP UX), Apple's macOS, and Unix like operating systems (such as Linux and FreeBSD). It is also available to operating systems such as Acorn RISC OS, AmigaOS, the classic Mac OS, OpenVMS, MS DOS, Microsoft Windows, OS/2, ArcaOS, Novell NetWare, and IBM i. Alternative remote file access protocols include the Server Message Block (SMB, also termed CIFS), Apple Filing Protocol (AFP), NetWare Core Protocol (NCP), and OS/400 File Server file system (QFileSvr.400). SMB and NetWare Core Protocol (NCP) occur more often than NFS on systems running Microsoft Windows; AFP occurs more often than NFS in Apple Macintosh systems; and QFileSvr.400 occurs more often in IBM i systems. Haiku in 2012 added NFSv4 support as part of a Google Summer of Code project.

During the development of the ONC protocol (called SunRPC at the time), only Apollo's Network Computing System (NCS) offered comparable functionality. Two competing groups developed over fundamental differences in the two remote procedure call systems. Arguments focused on the method for data encoding — ONC's External Data Representation (XDR) always rendered integers in big endian order, even if both peers of the connection had little endian machine architectures, whereas NCS's method attempted to avoid byte swap whenever two peers shared a common endianness in their machine architectures. An industry group called the Network Computing Forum formed (March 1987) in an (ultimately unsuccessful) attempt to reconcile the two network computing environments. In 1987, Sun and AT&T announced they would jointly develop AT&T's UNIX System V Release 4. This caused many of AT&T's other licensees of UNIX System to become concerned that this would put Sun in an advantaged position, and ultimately led to Digital Equipment, HP, IBM, and others forming the Open Software Foundation (OSF) in 1988. Ironically, Sun and AT&T had formerly competed over Sun's NFS versus AT&T's Remote File System (RFS), and the quick adoption of NFS over RFS by Digital Equipment, HP, IBM, and many other computer vendors tipped the majority of users in favor of NFS. NFS interoperability was aided by events called "Connectathons" starting in 1986 that allowed vendor neutral testing of implementations with each other. OSF adopted the Distributed Computing Environment (DCE) and the DCE Distributed File System (DFS) over Sun/ONC RPC and NFS. DFS used DCE as the RPC, and DFS derived from the Andrew File System (AFS); DCE itself derived from a suite of technologies, including Apollo's NCS and Kerberos.

Sun Microsystems and the Internet Society (ISOC) reached an agreement to cede "change control" of ONC RPC so that the ISOC's engineering standards body, the Internet Engineering Task Force (IETF), could publish standards documents (RFCs) related to ONC RPC protocols and could extend ONC RPC. OSF attempted to make DCE RPC an IETF standard, but ultimately proved unwilling to give up change control. Later, the IETF chose to extend ONC RPC by adding a new authentication flavor based on Generic Security Services Application Program Interface (GSSAPI), RPCSEC GSS, to meet IETF requirements that protocol standards have adequate security. Later, Sun and ISOC reached a similar agreement to give ISOC change control over NFS, although writing the contract carefully to exclude NFS version 2 and version 3. Instead, ISOC gained the right to add new versions to the NFS protocol, which resulted in IETF specifying NFS version 4 in 2003.