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Friday, February 5, 2010

Implementation techniques and Remote File Access for Distributed File Systems

Implementation of transparent naming requires a provision for the mapping of a file name to the associated location. Keeping this mapping manageable calls for aggregating sets of files into component units, and providing the mapping on a component unit basis rather than on a single file basis. To enhance the availability of the crucial mapping information, methods like replication, local caching, or both can be used.
A non-transparent mapping technique:
name ----> < system, disk, cylinder, sector >
A transparent mapping technique:
name ----> file_identifier ----> < system, disk, cylinder, sector >
So, when changing the physical location of a file, only the file identifier need be modified. This identifier must be "unique" in the universe.

Remote File Access
In remote-service mechanism, requests for accesses are delivered to the server, the server machine performs the accesses, and their results are forwarded back to the user. The remote-service method is analogous to performing a disk access for each access request. To ensure reasonable performance of a remote-service mechanism, caching is used. In DFSs, the goal is to reduce both network traffic and disk I/O.

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