A19_DFS1 - Distributed File Systems Architecture 11.1...

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Distributed File Systems Architecture – 11.1 Processes – 11.2 Communication – 11.3 Naming – 11.4
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Definition of a DFS DFS: multiple users, multiple sites, and (possibly) distributed storage of files. Benefits File sharing Uniform view of system from different clients Centralized administration Goals of a distributed file system Network Transparency (access transparency) Availability
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Goals Network (Access)Transparency Users should be able to access files over a network as easily as if the files were stored locally. Users should not have to know the location of a file to access it. Transparency can be addressed through naming and file mounting mechanisms
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Components of Access Transparency Location Transparency: file name doesn’t specify physical location (Ch. 1) Location Independence: files can be moved to new physical location, no need to change references to them. (A name is independent of its addresses – see Ch. 5) Location independence → location transparency, but the reverse is not necessarily true.
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Goals Availability : files should be easily and quickly accessible. The number of users, system failures, or other consequences of distribution shouldn’t compromise the availability. Addressed mainly through replication.
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Architectures Client-Server Traditional; e.g. Sun Microsystem Network File System (NFS) Cluster-Based Client-Server; e.g., Google File System (GFS) Symmetric Fully decentralized; based on peer-to-peer technology e.g., Ivy (uses a Chord DHT approach)
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Client-Server Architecture One or more machines (file servers) manage the file system. Files are stored on disks at the servers Requests for file operations are made from clients to the servers. Client-server systems centralize storage and management; P2P systems decentralize it.
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Communication Network cache cache cache cache Server Server Server Disks client client Architecture of a distributed file system: client-server model
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Sun’s Network File System Sun’s NFS for many years was the most widely used distributed file system. NFSv3: version three, used for many years NFSv4: introduced in 2003 Version 4 made significant changes
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Overview NFS goals: Each file server presents a standard view of its local file system transparent access to remote files compatibility with multiple operating systems and platforms. easy crash recovery at server (at least v1-v3) Originally UNIX based; now available for most operating systems. NFS communication protocols lets processes running in different environments share a file system.
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NFS Implements Remote Access Client Server Client Server Requests from client to access remote file (with server responses) File stays at server File is moved to client Client accesses file File is returned to the server Remote Access Model Upload/download model e.g., FTP
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Access Models Most distributed file systems use the
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This note was uploaded on 12/14/2011 for the course CS 690 taught by Professor Staff during the Fall '11 term at University of Alabama - Huntsville.

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A19_DFS1 - Distributed File Systems Architecture 11.1...

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