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After studying this chapter, you should be able to: Discuss basic concepts related to concurrency, such as race conditions, OS concerns, and mutual exclusion requirements; understand hardware approaches to supporting mutual exclusion; define and explain semaphores; define and explain monitors. | Module 17: Distributed-File Systems Background Naming and Transparency Remote File Access Stateful versus Stateless Service File Replication Example Systems Applied Operating System Concepts 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. Applied Operating System Concepts 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 | Module 17: Distributed-File Systems Background Naming and Transparency Remote File Access Stateful versus Stateless Service File Replication Example Systems Applied Operating System Concepts 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. Applied Operating System Concepts 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. Applied Operating System Concepts 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. Applied Operating System Concepts 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 machines. Location .
