LM.Lecture8 - Distributed Operating Systems CS551 Colorado...

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Unformatted text preview: Distributed Operating Systems CS551 Colorado State University at Lockheed-Martin Lecture 8 -- Spring 2001 4 April 2001 CS-551, Lecture 8 2 CS551: Lecture 8 ■ Topics – Distributed File Systems (Chapter 8) ■ Distributed Name Service ■ Distributed File Service ■ Distributed Directory Service ■ NFS ■ X.500 – Distributed Synchronization (Chapter 10) ■ Global Time ■ Physical Clocks ■ Network Time Protocol (NTP) ■ Logical Clocks 4 April 2001 CS-551, Lecture 8 3 Definitions ■ DFSs “support the sharing of information in the form of files throughout an intranet. A well-designed file service provides access to files stored at a server with performance and reliability similar to … files stored on local disks. A distributed file system enables programs to store and access remote files exactly as they do local ones, allowing users to access files from any computer in an intranet.” (Coulouris, Dollimore, Kindberg, 2001) 4 April 2001 CS-551, Lecture 8 4 Definitions, continued ■ “…in a DS, it is important to distinguish between the concepts of the file service and the file server. The file service is the specification of what the file system offers to its clients … the file system’s interface to the clients. A file server , in contrast, is a process that runs on some machine and helps implement the file service. A system may have one file server or several.” (Tanenbaum, 1995) 4 April 2001 CS-551, Lecture 8 5 Upload/Download Model Server Client Client’s copy Updated File Original File Adapted from Tanenbaum (1995) 4 April 2001 CS-551, Lecture 8 6 Remote Access Model Server Client Client requests access from remote file File does not move Adapted from Tanenbaum (1995) 4 April 2001 CS-551, Lecture 8 7 Terms ■ File system – “an abstract view of secondary storage” – “responsible for ■ Global naming ■ File access ■ Overall file organization” ■ Distributed Name Service – “focuses on the issues related to filenames” 4 April 2001 CS-551, Lecture 8 8 Basic File Systems ■ File Storage – Structured versus non-structured ■ File Attributes – File name, size, owner, creation/modification dates, version, protection information ■ File Protection Modes – Read, write, execute, append, truncate, delete 4 April 2001 CS-551, Lecture 8 9 Figure 8.4 Structured versus Unstructured Files. 4 April 2001 CS-551, Lecture 8 10 Figure 8.5 Access Matrix. 4 April 2001 CS-551, Lecture 8 11 Figure 8.6 Access List for File 1. 4 April 2001 CS-551, Lecture 8 12 Goals of a DFS ■ Network Transparency – Looks like a traditional file system on a mainframe – User need not know a file’s location ■ High Availability – Users should have easy access to files, wherever the users or files are located – Tolerant of failures 4 April 2001 CS-551, Lecture 8 13 Architecture ■ On the Network – File servers: hold the files – Clients: make accesses to the servers ■ Name Server (does name resolution) – Maps names to directories/files...
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This note was uploaded on 06/12/2011 for the course CS 551 taught by Professor Staff during the Summer '08 term at Colorado State.

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LM.Lecture8 - Distributed Operating Systems CS551 Colorado...

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