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NETWORK FILE SYSTEM

Nisarg Patel

08BCE056

Guided by:

Mr. Tejas Mehta

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TOPICS COVERED

1. NFS Introduction

2. Versions of NFS

3. Overview of NFSv2, NFSv3, NFSv4

4. NFSv2 detailed study

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INTRODUCTION

Network File System (NFS) is a network file system protocoloriginally developed by Sun Microsystems in 1984, allowing a

user on a client computer to access files over a network in amanner similar to how local storage is accessed.

NFS, like many other protocols and it works with RemoteProcedure Call.

The Network File System is an open standard defined in RFCs,allowing anyone to implement the protocol.

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HOW AN NFS WORKS?

A Network File System has mainly two parts- a client & a

server.A client is a remote user who has a directory on a

server, which is connected through a network.

Every user makes an Remote Procedure Call from their local

machine to the network server. This call is processed by

various daemons loaded on the server, and an appropriate

response is given to the client.

Thus a user can access their files & directories stored on the

server.

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REMOTE PROCEDURE CALL

Remote Procedure Callspecification provides a procedure-oriented interface to remote services.

Each consists of a program that is a set of procedures. NFS isone such "program".

The combination of host address, program number, and

procedure number specifies one remote service procedure.

RPC is Protocol Independent, so it can be used with anyunderlying transport protocol.

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VERSIONS OF NFS

Mainly there are three versions of Network File Systems used

till date version 2, version 3 & version 4.

Sun used version 1 only for in-house experimental purposes.

When the development team added substantial changes to

NFS version 1 and released it outside of Sun, they decided torelease the new version as version 2.

Well study version 3 & 4 later in detail

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NFSv2 Detailed Study

Following topics are discussed under NFSv2:

External Data Representation & Remote Procedure Call

Stateless Servers

File System Model

RPC Information

Size Of XDR Structures Basic Data Types

Server Procedures

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OVERVIEW

The NFS protocol is designed to be machine, operating system,network architecture, and transport protocol independent.

This independence is achieved through the use of RemoteProcedure Call (RPC) primitives built on top of an eXternalData Representation (XDR).

It performs the operating system-specific functions that allow,

for example, to attach remote directory trees to some local filesystem.

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XDR & RPC

The External Data Representation (XDR) standard provides acommon way of representing a set of data types over a

network.

Sun provides implementations of XDR & RPC, but NFS doesnot require their use.

Any software that provides equivalent functionality can be used,

and if the encoding is exactly the same it can interoperate withother implementations of NFS.

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STATELESS SERVERS

The NFS protocol is stateless. That is, a server does not needto maintain any extra state information about any of its clients in

order to function correctly.

With stateless servers, a client need only retry a request untilthe server responds; it does not even need to know that theserver has crashed, or the network temporarily went down.

The client of a stateful server, on the other hand, needs toeither detect a server crash and rebuild the servers state whenit comes back up, or cause client operations to fail.

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FILE SYSTEM MODEL

NFS assumes a file system that is hierarchical, with directoriesas all but the bottom-level files.

Each entry in a directory (file, directory, device, etc.) has astring name. Pathname is the concatenation of all the"components" (directory and file names) in the name.

A "filesystem" is a tree on a single server(usually a single diskor physical partition) with a specified "root".

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RPC Information

Authentication

The NFS service usesAUTH_UNIX,AUTH_DES, or

AUTH_SHORTstyle authentication, except in the NULLprocedure whereAUTH_NONEis also allowed.

Transport Protocols

NFS currently is supported on UDP/IP.

Port NumberThe NFS protocol currently uses the UDP port number 2049.

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Size OfXDR Structures

These are the sizes, given in decimal bytes, of various XDR structuresused in the protocol:

//The maximum number of bytes of data in a READ or WRITE request

const MAXDATA = 8192;

// The maximum number of bytes in a pathname argument

const MAXPATHLEN=1024;

// The maximum number of bytes in a file name argument

const MAXNAMLEN= 255;

// The size in bytes of the opaque "cookie" passed by READDIR

const COOKIESIZE= 4;

// The size in bytes of the opaque file handle

const FHSIZE= 32;

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BASIC DATA TYPES

enum stat;

The stattype is returned with every procedures results & it

indicates the state of procedure.

enum ftype;

The enumeration ftype gives the type of a file.

typedef opaque fhandle[FHSIZE];

The fhandle is the file handle passed between the server and

the client.

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BASIC DATA TYPES

struct timeval

The timevalstructure is used to pass the time and date

information.

struct fattr

The fattrstructure contains the attributes of a file like -"type,

"nlink, "uid, "gid, "size, "rdev, etc.

struct sattr

The sattrstructure contains the file attributes which can be set

from the client.

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BASIC DATA TYPES

typedef string filename;

The type filename is used for passing file names or pathname

components.

typedef stringpath;

The typepath is a pathname.

struct diropargs

The diropargs structure is used in directory operations.

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CONCLUSIONS

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TOPICS THAT WILL BE COVERED

NFSv3 Detailed Study

NFSv4 Detailed Study