Network File System
(NFS)
Chunyan Zhu
08/16/2000
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Introduction
File system is a component of OS. Organization,
storage, retrieve, naming,sharing, protection...
NFS is designed to be portable across different
machine, OS, network architecture, and
transport protocols.
Three topic : NFS design principles, NFS
architecture, Implementation issues.
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NFS design principle
Transparent Access: Users and applications can
access remote files as if they were local.
Portability: NFS is machine and operating system
independent.
Fast Recovery From Failure: NFS is designed to
recover quickly from system failures and network
problems.
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NFS design principle
Network Protocol Independence: NFS has the
ability to run on multiple transport protocols instead of
being restricted to just one. This means new protocol in
the future will not be a problem for NFS.
Performance: NFS is designed for high performance.
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NFS architecture
The NFS protocol provides the medium for
communication between client and server
processes over the network.
Virtual file system.
NFS server.
NFS client.
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NFS architecture
Client
Computer
Server
Computer
UNIX Kernel
UNIX Kernel
Virtual
File System
Virtual
File System
User Processes
UNIX File
System
Disks
NFS Client
NFS
Server
UNIX File
System
Disks
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Virtual file system
A Virtual File System (VFS) module has been
added to the UNIX kernel to distinguish local
and remote files. And translate the UNIXindependent file identifiers used by NFS and the
internal file identifiers used in UNIX.
The file identifiers used in NFS are called file
handlers.
( File system identifier + i-node
number of file + i-node generation number)
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NFS server
The role of the NFS server is to allow its disk file
systems to be shared by other machines. The
process is called exporting.
To export a file system :
The full pathname of the directory to be exported
The client machines that will have access to the
exported directory
Any access restrictions
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NFS client
To access the remote file system in the server,
the client needs to specify:
The remote host name
pathname of a directory in the remote file
system
The local name with which it is to be
mounted
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NFS client
Client
Server
/ (root)
/ (root)
home
export
students
people
ann
bob
Local and remote file systems
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Implementation issues
Stateless server.
A server should not need to maintain any protocol
state information about it’s client
A client need only retry a request until the server
responds
Caching. Temporary storage of file data in a
fast access local storage called cache.
Once file data is cached, client requests go directly to
the cache and do not require a data transfer over the
network.
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Implementation issues
The NFS client can anticipate future data
requirements through a process called "read- ahead"
Security model
The server must check the user’s identity against the
file’s access permission
Sun RPC requires clients to send UNIX user ID.
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An NFS example on Solaris
Assume the server name is earth.cs.seu.edu and the
client name is moon.cs.seu.edu
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An NFS example on Solaris
NFS Server Processes
mountd: Mount requests are handled by the
mountd daemon
nsfd: Once a client’s mount request has been valid
by mountd, it is allowed to request various file
system operations
NFS Client Process
automountd: Attach a remote file system to the local
file system
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An NFS example on Solaris
Exporting file system on server machine
Editing file: /etc/dfs/dfstab
share -F nfs -o rw=moon.cs.seu.edu
/export/people
Mounting file system on client machine
Editing file: /etc/vfstab
earth.cs.seu.edu:/export/people /home/student nfs 0 yes rw
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Summary
Client-server architecture
Location and access transparency
Stateless server
High performance by client caching
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