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Lecture Operating system concepts - Chapter 16: Distributed-file systems

Chapter 16 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. | Chapter 16 Distributed-File Systems I Background I Naming and Transparency I Remote File Access I Stateful versus Stateless Service I File Replication I Example Systems Operating System Concepts 16.1 Silberschatz, Galvin and Gagne 2002 Background I 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. I A DFS manages set of dispersed storage devices I Overall storage space managed by a DFS is composed of different, remotely located, smaller storage spaces. I There is usually a correspondence between constituent storage spaces and sets of files. Operating System Concepts 16.2 Silberschatz, Galvin and Gagne 2002 DFS Structure I Service – software entity running on one or more machines and providing a particular type of function to a priori unknown clients. I Server – service software running on a single machine. I Client – process that can invoke a service using a set of operations that forms its client interface. I A client interface for a file service is formed by a set of primitive file operations (create, delete, read, write). I Client interface of a DFS should be transparent, i.e., not distinguish between local and remote files. Operating System Concepts 16.3 Silberschatz, Galvin and Gagne 2002 Naming and Transparency I Naming – mapping between logical and physical objects. I Multilevel mapping – abstraction of a file that hides the details of how and where on the disk the file is actually stored. I A transparent DFS hides the location where in the network the file is stored. I 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. Operating System Concepts 16.4 Silberschatz, Galvin and Gagne 2002 Naming Structures I Location transparency – file name does not reveal the file’s physical .