ch17 - perating System Concepts with Java – 7 th Edition,...

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Unformatted text preview: perating System Concepts with Java – 7 th Edition, Nov 15, 2006 Silberschatz, Galvin and Gagne ©2007 Chapter 17: Distributed-File Systems 17.2 Silberschatz, Galvin and Gagne ©2007 Operating System Concepts with Java – 7 th Edition, Nov 15, 2006 Chapter 17 Distributed-File Systems ¡ Background ¡ Naming and Transparency ¡ Remote File Access ¡ Stateful versus Stateless Service ¡ File Replication ¡ An Example: AFS 17.3 Silberschatz, Galvin and Gagne ©2007 Operating System Concepts with Java – 7 th Edition, Nov 15, 2006 Chapter Objectives ¡ To explain the naming mechanism that provides location transparency and independence ¡ To describe the various methods for accessing distributed files ¡ To contrast stateful and stateless distributed file servers ¡ To show how replication of files on different machines in a distributed file system is a useful redundancy for improving availability ¡ To introduce the Andrew file system (AFS) as an example of a distributed file system 17.4 Silberschatz, Galvin and Gagne ©2007 Operating System Concepts with Java – 7 th Edition, Nov 15, 2006 Background ¡ Distributed file system ( DFS ) – a distributed implementation of the classical time-sharing model of a file system, where multiple users share files and storage resources ¡ A DFS manages set of dispersed storage devices ¡ Overall storage space managed by a DFS is composed of different, remotely located, smaller storage spaces ¡ There is usually a correspondence between constituent storage spaces and sets of files 17.5 Silberschatz, Galvin and Gagne ©2007 Operating System Concepts with Java – 7 th Edition, Nov 15, 2006 DFS Structure ¡ Service – software entity running on one or more machines and providing a particular type of function to a priori unknown clients ¡ Server – service software running on a single machine ¡ Client – process that can invoke a service using a set of operations that forms its client interface ¡ A client interface for a file service is formed by a set of primitive file operations (create, delete, read, write) ¡ Client interface of a DFS should be transparent, i.e., not distinguish between local and remote files 17.6 Silberschatz, Galvin and Gagne ©2007 Operating System Concepts with Java – 7 th Edition, Nov 15, 2006 Naming and Transparency ¡ Naming – mapping between logical and physical objects ¡ Multilevel mapping – abstraction of a file that hides the details of how and where on the disk the file is actually stored ¡ A transparent DFS hides the location where in the network the file is stored ¡ For a file being replicated in several sites, the mapping returns a set of the locations of this file’s replicas; both the existence of multiple copies and their location are hidden 17.7 Silberschatz, Galvin and Gagne ©2007 Operating System Concepts with Java – 7 th Edition, Nov 15, 2006 Naming Structures ¡ Location transparency – file name does not reveal the file’s physical storage location...
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ch17 - perating System Concepts with Java – 7 th Edition,...

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