A distributed file system stores files in several nodes of a distributed system, so a process and a file used by it might be in different nodes of a system. Performance and reliability of a distributed file system are determined by the manner in which it organizes access to a required file. This chapter discusses different methods of organizing access to files and directories located in various nodes of a system, and techniques such as file caching and stateless file servers that are used to ensure good performance and reliability, respectively. | Chapter 20 Distributed File Systems Copyright © 2008 Operating Systems, by Dhananjay Dhamdhere Introduction Design Issues in Distributed File Systems Transparency Semantics of File Sharing Fault Tolerance DFS Performance Case Studies 20. Operating Systems, by Dhananjay Dhamdhere Copyright © 2008 Operating Systems, by Dhananjay Dhamdhere Design Issues in Distributed File Systems 20. Operating Systems, by Dhananjay Dhamdhere Copyright © 2008 Operating Systems, by Dhananjay Dhamdhere Overview of DFS Operation Remote file processing model File server agent and client agent are analogous to RPC’s stub processes For efficiency, the client agent and the cache manager are typically rolled into a single unit 20. Operating Systems, by Dhananjay Dhamdhere Copyright © 2008 Operating Systems, by Dhananjay Dhamdhere Transparency In a conventional file system, a user identifies a file through a path name User is aware that file belongs in a specific directory, but is not | Chapter 20 Distributed File Systems Copyright © 2008 Operating Systems, by Dhananjay Dhamdhere Introduction Design Issues in Distributed File Systems Transparency Semantics of File Sharing Fault Tolerance DFS Performance Case Studies 20. Operating Systems, by Dhananjay Dhamdhere Copyright © 2008 Operating Systems, by Dhananjay Dhamdhere Design Issues in Distributed File Systems 20. Operating Systems, by Dhananjay Dhamdhere Copyright © 2008 Operating Systems, by Dhananjay Dhamdhere Overview of DFS Operation Remote file processing model File server agent and client agent are analogous to RPC’s stub processes For efficiency, the client agent and the cache manager are typically rolled into a single unit 20. Operating Systems, by Dhananjay Dhamdhere Copyright © 2008 Operating Systems, by Dhananjay Dhamdhere Transparency In a conventional file system, a user identifies a file through a path name User is aware that file belongs in a specific directory, but is not aware of its location in the system Location info field of the file’s directory entry indicates the file’s location on disk Location transparency can be provided in a DFS through a similar mechanism Location info: (node id, location) Location independence requires information in location info field to vary dynamically 20. Operating Systems, by Dhananjay Dhamdhere Copyright © 2008 Operating Systems, by Dhananjay Dhamdhere Semantics of File Sharing Semantics determine manner in which effect of file manipulations performed by concurrent users of a file are visible to one another 20. Operating Systems, by Dhananjay Dhamdhere Copyright © 2008 Operating Systems, by Dhananjay Dhamdhere Semantics of File Sharing (continued) A session consists of some clients of a file that are located in the same node of a system Problem with session semantics: poor portability Session semantics are easy to implement in a DFS employing file caching File changes are not visible to clients in .
