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Lecture Operating system concepts (Fifth edition): Module 17 - Avi Silberschatz, Peter Galvin

Module 17 - Distributed-file systems. Chapter 17 looks at the current major research and development in distributed-file systems (DFS). The purpose of a DFS is to support the same kind of sharing when the files are physically dispersed among the various sites of a distributed system. | Lecture Operating system concepts Fifth edition Module 17 - Avi Silberschatz Peter Galvin Module 17 Distributed-File Systems Background Naming and Transparency Remote File Access Stateful versus Stateless Service File Replication Example Systems 17.1 Silberschatz Galvin and Gagne 1999 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. 17.2 Silberschatz Galvin and Gagne 1999 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. 17.3 Silberschatz Galvin and Gagne 1999 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. 17.4 Silberschatz Galvin and Gagne 1999 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 .