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 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. 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 . not distinguish between local and remote files. 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. 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 .
