Explain File Access Models. (December 2017) (10 Marks).

Q. Explain File Access Models. (December 2017) (10 Marks ).

Ans - The specific client's request for accessing a particular file is serviced on the basis of the file accessing model used by the distributed file system.The file accessing model basically depends on 

1. the unit of data access and 
2. the method used for accessing remote files.

On the basis of the unit of data access, following file access models might be used in order to access the specific file.

1.     File-level transfer model
2.     Block-level transfer model
3.     Byte-level transfer model
4.     Record-level transfer model

1.File-level transfer model: In file-level transfer model, the complete file is moved while a particular operation necessitates the file data to be transmitted all the way through the distributed computing network amongst client and server. This model has better scalability and is efficient.

2.Block-level transfer model: In block-level transfer model, file data transfers through the network amongst client and a server is accomplished in units of file blocks. In short, the unit of data transfer in block-level transfer model is file blocks. The block-level transfer model might be used in distributed computing environment comprising several diskless workstations.

3.Byte-level transfer model: In byte-level transfer model, file data transfers the network amongst client and a server is accomplished in units of bytes. In short, the unit of data transfer in byte-level transfer model is bytes. The byte-level transfer model offers more flexibility in comparison to the other file transfer models since, it allows retrieval and storage of an arbitrary sequential subrange of a file. The major disadvantage of byte-level transfer model is the trouble in cache management because of the variable-length data for different access requests.

4.Record-level transfer model: The record-level file transfer model might be used in the file models where the file contents are structured in the form of records. In record-level transfer model, file data transfers through the network amongst client and a server is accomplished in units of records. The unit of data transfer in record-level transfer model is record.