Network File System (NFS)
Sun Microsystems Inc. created NFS as an answer to problems with working in harmony across networks supporting many operating systems. NFS supports file sharing only and is now an integral part of many Unix-based operating systems. It is also well supported by most other operating systems.
NFS versions 1 and 2 used UDP as the primary transport protocol. Because UDP does not provide reliable delivery, reliable delivery had to be handled by NFS itself for unreliable links. Some of the early implementations of NFS had file corruption problems. Starting with NFS version 3, NFS can alternatively use TCP as the transport protocol. Actually, TCP support was available in NFS version 3 but was not optimized. With TCP as the transport protocol, NFS can use the reliability of TCP to provide better delivery over unreliable links. Consequently, NFS version 3 works better over WAN links and the Internet.
An NFS version 4 has been proposed but most commercial implementations either implement NFS version 2 or version 3.
Pure NFS has no way of preventing various users from writing to a single file at the same time, allowing users to easily corrupt files at will without knowledge of other file activity. However, a file-locking mechanism implemented by a Network Lock Manager (NLM) protocol can be used in conjunction with NFS to enable file sharing and overwriting between multiple users.
NFS file access is seamless and transparent. After an NFS volume is mounted, it becomes part of the end user's system. There are no additional steps, beyond the export process, of course. Exporting is required to synchronize both server and clients to the NFS configuration. This system is neither simple nor administrator friendly.