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

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Chapter 17: Distributed-File Systems Chapter 17: Distributed-File Systems Adapted to COP4610 by Robert van Engelen
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17.2 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Apr 4, 2005 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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17.3 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Apr 4, 2005 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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17.4 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Apr 4, 2005 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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17.5 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Apr 4, 2005 Naming Structures Naming Structures Location transparency file name does not reveal the file’s physical storage location Location independence – file name does not need to be changed when the file’s physical storage location changes
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17.6 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Apr 4, 2005 Naming Schemes — Three Main Approaches Naming Schemes — Three Main Approaches Files named by combination of their host name and local name; guarantees a unique systemwide name Attach remote directories to local directories, giving the appearance of a coherent directory tree; only previously mounted remote directories can be accessed transparently Total integration of the component file systems A single global name structure spans all the files in the system If a server is unavailable, some arbitrary set of directories on different machines also becomes unavailable
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17.7 Silberschatz, Galvin and Gagne ©2005
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ch17 - Chapter 17 Distributed-File Systems Chapter Adapted...

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