Chapter 19 – Service-oriented Architecture Lecture 1 1Chapter 19 Service-oriented architecture.
4.file service architecture (1)
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Transcript of 4.file service architecture (1)
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DISTRIBUTED FILE SYSTEMS(DFS)
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DISTRIBUTED FILE SYSTEMS
• Including1.Introduction2.File Service Architecture3.Case Study: Sun NFS
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1. Introduction
1. Characteristics of file system
2. Distributed File system requirements
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2. File service architecture providing access to files is obtained by structuring
the file service as three components:
1. Flat file service2. Directory service3. Client module.
The relevant modules and their relationship is shown in Figure
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File Service Architecture
Client computer Server computer
Applicationprogram
Applicationprogram
Client module
Flat file service
Directory service
LookupAddNameUnNameGetNames
ReadWriteCreateDeleteGetAttributesSetAttributes
*
Figure 8.5
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• Responsibilities of various modules can be defined as follows:
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1. Flat file service
• Concerned with the implementation of operations on the contents of file.
• Unique File Identifiers (UFIDs) are used to refer to files in all requests for flat file service operations.
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Flat file service operations
1. Read
2. Write
3. Create
4. Delete
5. GetAttributes
6. SetAttributes
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1. Read(FileId, i, n) :
Reads a sequence of up to n items from a file
starting at item i.
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2. Write(FileId, i, Data) :
Write a sequence of Data to a file, starting
at item i.
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3. Create() :
Creates a new file of length0 and delivers a UFID for it.
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4. Delete(FileId) :Removes the file from the file store.
5. GetAttributes(FileId) : Returns the file attributes for the file.
6. SetAttributes(FileId, Attr) :Sets the file
attributes.
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2. Directory service
• Provides mapping between text names for the files and their UFIDs.
• Clients may obtain the UFID of a file by quoting its text name to directory service.
• Directory service supports functions to add new files to directories.
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Directory service operations
1. Lookup
2. AddName
3. UnName
4. GetNames
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Directory service operations
1. Lookup(Dir, Name) : Locates the text name in the directory and returns the relevant UFID.
If Name is not in the directory, throws an exception.
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2. AddName(Dir, Name, File) :If Name is not in
the directory, adds(Name,File) to the
directory and updates the
file’s attribute record.
• If Name is already in the directory: throws an
exception.
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3. UnName(Dir, Name) :If Name is in the
directory, the entry containing Name is
removed from the directory.
• If Name is not in the directory: throws an
exception.
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4. GetNames(Dir, Pattern):Returns all the text
names in the directory that match the regular
expression Pattern.
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3. Client module
• It runs on each computer and provides integrated service (flat file and directory) as a single API to application programs.
• It holds information about the network locations of flat-file and directory server processes.
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Access control
• In distributed implementations, access rights checks have to be performed at the server .
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Hierarchic file system
• A hierarchic file system consists of a number of directories arranged in a tree structure.
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File Group
• A file group is a collection of files that can be located on any server.
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Thank You