What is NFS?
Network File System (NFS) is a protocol originally developed by Sun Microsystems in 1984.
“A distributed file system where data is held on a central server and served to end users so it appears as if it is on the local system”.
This allows data sharing across multiple platforms without copying.
It is the most common distributed file system in use on Unix/Linux systems.

Why NFS?
Machine and Operating System Independence
Fast Crash Recovery
o When a server crashes, client just resends request until it gets an answer from the rebooted server
o Client cannot tell difference between a server that has crashed and recovered and a slow server
Transparent Access
o Remote files should be accessed in exactly the same way as local files
UNIX semantics should be maintained on client
“Reasonable” performance.

Platforms
Though the use of NFS occurs most commonly with UNIX systems, other software platforms such as the classic Mac OS, Microsoft Windows, Novell NetWare, and IBM AS/400 operating systems can also use the protocol. (Alternative remote file access protocols include the Server Message Block (SMB, also known as CIFS) protocol, 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 commonly than NFS on systems running Microsoft Windows; AFP occurs more commonly than NFS in Macintosh systems; and QFileSvr.400 occurs more commonly in AS/400 systems.)

NFS Architecture:

Basic design For NFS:
Three important parts
o The protocol
o The server side
o The client side

The protocol
Uses the Sun RPC mechanism and Sun eXternal Data Representation (XDR) standard
Defined as a set of remote procedures
Protocol is stateless
o Each procedure call contains all the information necessary to complete the call
o Server maintains no “between call” information

Server side
The server side is represented by the local VFS actually storing the data
Plus Various daemons (as shown in Table 1)
NFS is stateless—servers do not keep track of clients
Each NFS operation must be self-contained
o From server’s point of view

Daemon Description
nfsd The NFS daemon which services requests from the NFS clients.
mountd The NFS mount daemon which carries out the requests that nfsd(8) passes on to it.
rpcbind This daemon allows NFS clients to discover which port the NFS server is using.
biod biod daemon does readahead for clients
rpc.lockd rpc.lockd provides locking.rpc.lockd handles lock recovery when server crashes

[Table 1]

Client Side
Provides transparent interface to NFS
Mapping between remote file names and remote file addresses is done a server boot time through remote mount
o Extension of UNIX mounts
o Specified in a mount table
o Makes a remote subtree appear part of a local subtree

Practical Uses
Set several machines to share a CDROM or other media among them. This is cheaper and often a more convenient method to install software on multiple machines.
On large networks, it might be more convenient to configure a central NFS server in which to store all the user home directories. These home directories can then be exported to the network so that users would always have the same home directory, regardless of which workstation they log in to.
Several machines could have a common /usr/ports/distfiles directory. That way, when you need to install a port on several machines, you can quickly access the source without downloading it on each machine.

Operations supported by NFS

Hard Issues
Performance is average at best and doesn’t scale well.
Maintaining a truly distributed file system can be
omplicated if many machines supply data.
Locking is not good and can cause problems when used simultaneously by multiple applications.
NFS root file systems cannot be shared
NFS tries to preserve UNIX open file semantics but does not always succeed
Not Secure.