ch17 - Chapter 17: Distributed-File Systems Chapter 17...

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Chapter 17: Distributed-File Systems Chapter 17: Distributed-File Systems
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17.2 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts Chapter 17 Distributed-File Systems Chapter 17 Distributed-File Systems Background Naming and Transparency Remote File Access Stateful versus Stateless Service File Replication An Example: AFS
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17.3 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts Chapter Objectives 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
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17.4 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts Background 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
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17.5 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts DFS Structure 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
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17.6 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts Naming and Transparency 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
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17.7 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts Naming Structures Naming Structures Location transparency file name does not reveal the file’s physical storage location File name still denotes a specific, although hidden, set of physical disk blocks Convenient way to share data Can expose correspondence between component units and
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This note was uploaded on 01/21/2012 for the course COMPUTER CSCI 593 taught by Professor Hamnes during the Spring '11 term at Aston University.

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ch17 - Chapter 17: Distributed-File Systems Chapter 17...

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