1. Network File System (NFS)
Chunyan Zhu
08/16/2000

2. 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.

3. 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.

4. 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.

5. 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.

6. NFS architecture Client Computer Server Computer User Processes
UNIX Kernel
UNIX Kernel
Virtual
File System
Virtual
File System
UNIX File System
NFS Client
NFS
Server
UNIX File
System
Disks
Disks

7. 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 UNIX-independent 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)

8. 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

9. 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

10. NFS client Client Server / (root) / (root) home export students people
ann
bob
Local and remote file systems

11. 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.

12. 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.

13. An NFS example on Solaris
Assume the server name is earth.cs.seu.edu and the client name is moon.cs.seu.edu

14. 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

15. 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

16. Summary Client-server architecture Location and access transparency
Stateless server
High performance by client caching