Alternatives Of Network File System Essay Research — страница 3

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internet architecture .As such ,it is the principal body engaged in the development of anew internet standards and procedures. 2.1 The relation between the NFS server and Client file systems NFS consists of the NFS server and the NFS client software. The NFS server is implemented as a daemon, waiting for requests from clients. The NFS server does not retain the state of the NFS client. The NFS server daemon is multithreaded; it processes multiple NFS client calls, in parallel. The NFS server daemon is also an event-driven, asynchronous process. Each NFS client call contains all the information necessary to complete the request see Figure ( 1 ) . The NFS client software implements a state mechanism that maintains all information required for processing client requests. Each client

operation can be requested more than once and contains all the information necessary to complete the request. This model presumes no file open and close requests because these require saving the state of the object and that the server write data to the disk before returning the reply message to the user. When mounting a remote file system, an NFS client sends a message that makes the remote file system part of the local file directory. The remote host redirects operations that access files on the remote file system to the NFS client software. The NFS client and NFS server then exchange messages. Figure 1 The division of NFS between client and server NFS Follows the Client ?server model, in which the server is the system that owns the file system resource and is configured to

share it with other systems .An NFS-shareable resource is usually referred to as an exported file system. The client is the resource user .It uses the exported file system as if it were part of the local file system .To achieve this transparency, the client is said to mount the exported directory to the local file system. In Figure(2) , /efs is the exported directory on host netrix (the NFS server). To access that directory from client jade, it must be mounted first. To do that ,the administrator creates the /ifs directory to use as the mount directory and issues the appropriate mount command . Consecuently, to access the file budget.rpt from host jade, the user must specify /ifs/reports/budget.rpt as the path to that file. Figure 2 The relationship between the NFS server and

client file systems. To transparently access the file budget.rpt from host jade, the user mounts the exported directory /efs on NFS server netrix and specifies / ifs/report/budget.rpt as the path to the command. 3.1 Architecture of NFS NFS is designed to give users high performance, transparent access to server file systems on global networks. Some of the most important design principles are summarized below: Transparent Access: Users and applications can access remote files as if they were local. They are not required to know whether the files reside on the local disk or on remote servers. Portability: NFS is machine and operating system independent. This allows it to be ported easily to multiple OS and hardware platforms from PCs to mainframes. Fast Recovery From Failure: NFS

is designed to recover quickly from system failures and network problems, causing minimal disruption of service to users. Network Protocol Independence: NFS has the flexibility to run on multiple transport protocols instead of being restricted to just one. This allows it to utilize existing protocols today as well as new protocols in the future. Performance: NFS is designed for high performance so that users can access remote files as quickly as they can access local files. Security: The NFS architecture enables the utilization of multiple security mechanisms. This allows system administrators to choose the security mechanism that is appropriate for their distributed file sharing environment instead of being restricted to one solution. This also allows NFS to utilize new security

mechanisms in the future. These features are implemented within the NFS client/server framework which reduces costs by enabling heterogeneous resource sharing across the global enterprise. Servers make their file systems sharable through a process called exporting. Clients gain access to these file systems by adding them to their local file “tree” via the mount process. The NFS protocol provides the medium for communication between client and server processes over the network. 1.2 Alternative for NFS Naturally ,as a mechanism ,NFS has competitors .In particular ,integration of MS_DOS systems with file servers will certainly not be achieved by equipping all PCs with PC-NFS . For examples Remote File System (RFS), Open Software Foundation?s Distributed Computing Environment