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Unformatted text preview: ilesystems on a server. This
differs from FTP (Chapter 27), which provides file transfer. With FTP a complete copy of
the file is made. NFS accesses only the portions of a file that a process references, and a
goal of NFS is to make this access transparent. This means that any client application that
works with a local tile should work with an NFS file, without any program changes
NFS is a client-server application built using Sun RPC. NFS clients access tiles on an NFS
server by sending RPC requests to the server. While this could be done using normal user
processes - that is, the NFS client could be a user process that makes explicit RPC calls to
the server, and the server could also be a user process-NFS is normally not implemented
this way for two reasons. First, accessing an NFS tile must be transparent to the client.
Therefore the NFS client calls are performed by the client operating system, on behalf of
client user processes. Second, NFS servers are implemented within the operating system
on the server for efficiency. If the NFS server were a user process, every client request
and server reply (including the data being read or written) would have to cross the
boundary between the kernel and the user process, which is expensive.
In this section we look at version 2 of NFS, as documented in RFC 1094 [Sun
Microsystems 1988b]. A better description of Sun RPC, XDR, and NFS is given in
[X/Open 1991]. Details on using and administering NFS are in [Stern 1991]. The
specifications for version 3 of the NFS protocol were released in 1993, which we cover in
Figure 29.3 shows the typical arrangement of an NFS client and an NFS server. There are
many subtle points in this figure. file:///D|/Documents%20and%20Settings/bigini/Docu...homenet2run/tcpip/tcp-ip-illustrated/nfs_netw.htm (7 of 23) [12/09/2001 14.47.56] Chapter 29. NFS: Network File System Figure 29.3 Typical arrangement of NFS client and NFS server.
1. It is transparent to the client whether it's accessing a local file or an NFS...
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