3dfsdesign - File Service versus File Server File service:...

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File Service versus File Server File service: The file service is the specification of what the file system offers to its clients. It describes the primitives available, what parameters they takes, and what actions they perform. To clients, the file service defines precisely what service they can count on, but says nothing about how it is implemented. The file service specifies the file system’s interface to the clients. File server: A file server is a process that runs on some machine and helps implement the file service. A system may have one or more file servers, but don’t know what their location or function of each one. The clients should not even know that the file service is distributed. All the system knows is that when they call the procedures specified in the file service, the required work is performed and the required results are returned.
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Distributed File Servers Since file server is just a user process, a system can have one or more file server running at the same time with each of them offering a different file service. For example, a distributed system may have two file servers that offer UNIX file service and MS-DOS file service, with each user process using the one appropriate for it. So it is possible to have a terminal with multiple windows, with UNIX programs running in some windows and MS-DOS programs running in other windows, with no conflicts. Whether the servers offer specific file services, such as UNIX or MS-DOS, or more general file services is up to the system designers. The type and number if file services available may even change as the system evolves.
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Distributed File System Design A distributed file system typically has two reasonably distinct components: True file service: concerned with the operations on individual files, such as reading, writing, and appending. Directory service: concerned with creating and managing directories, adding and deleting files from directories, and so on. In many systems, such as UNIX and MS-DOS, a file is an un-interpreted sequence of bytes. The meaning and structure of the information in the files is entirely up to the application programs; the operating system is not interested. On mainframes, many types of files exist, each with different properties. A file can be structured as a sequence of records, for example, with operating system calls to read or write a particular record. The record can usually be specified by giving either its record number or the value of some field. The OS either maintains the file as a B-tree or other suitable data structure, or uses hash tables to locate records quickly. Since most distributed systems are intended for UNIX or MS-DOS environments, most file
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This note was uploaded on 09/17/2009 for the course IT it771 taught by Professor Jenisha during the Fall '09 term at University of Advancing Technology.

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3dfsdesign - File Service versus File Server File service:...

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