1. Tanenbaum & Van Steen, Distributed Systems: Principles and Paradigms, 2e, (c) 2007 Prentice-Hall, Inc. All rights reserved. 0-13-239227-5 1 DISTRIBUTED SYSTEMS Principles and Paradigms Second Edition ANDREW S. TANENBAUM MAARTEN VAN STEEN Chapter 11 DISTRIBUTED FILE SYSTEMS

2. Tanenbaum & Van Steen, Distributed Systems: Principles and Paradigms, 2e, (c) 2007 Prentice-Hall, Inc. All rights reserved. 0-13-239227-5 2 SCHEME 11.1 ARCHITECTURE 11.1.1 Client-Server Architectures 11.1.2 Cluster-Based Distributed File Systems 11.1.3 Symmetric Architectures 11.2 PROCESS 11.3 COMMUNICATION 11.3.1 RPCs in NFS 11.3.2 The RPC2 Subsystem 11.3.3 File-Oriented Communication in Plan 9

3. Tanenbaum & Van Steen, Distributed Systems: Principles and Paradigms, 2e, (c) 2007 Prentice-Hall, Inc. All rights reserved. 0-13-239227-5 3 SCHEME 11.4 NAMING 11.4.1 Naming in NFS 11.4.2 Constructing a Global Name Space 11.5 SYNCHRONIZATION 11.5.1 Semantics of File Sharing

4. Tanenbaum & Van Steen, Distributed Systems: Principles and Paradigms, 2e, (c) 2007 Prentice-Hall, Inc. All rights reserved. 0-13-239227-5 4 DISTRIBUTED FILE SYSTEMS Distributed file systems allow mutiple processes to share data over long periods of time in a secure and reliable way.

5. Tanenbaum & Van Steen, Distributed Systems: Principles and Paradigms, 2e, (c) 2007 Prentice-Hall, Inc. All rights reserved. 0-13-239227-5 5 DISTRIBUTED FILE SYSTEMS 1.File server provides a standardized view of its local file system. 2.Allowing a heterogeneous collection of processes to share a common file system.

6. Tanenbaum & Van Steen, Distributed Systems: Principles and Paradigms, 2e, (c) 2007 Prentice-Hall, Inc. All rights reserved. 0-13-239227-5 6 Client-Server Architectures (1) Figure 11-1. (a) The remote access model. (b) The upload/download model.

7. Tanenbaum & Van Steen, Distributed Systems: Principles and Paradigms, 2e, (c) 2007 Prentice-Hall, Inc. All rights reserved. 0-13-239227-5 7 Client-Server Architectures (2) Figure 11-2. The basic NFS architecture for UNIX systems.

8. Tanenbaum & Van Steen, Distributed Systems: Principles and Paradigms, 2e, (c) 2007 Prentice-Hall, Inc. All rights reserved. 0-13-239227-5 8 File System Model (1) Figure 11-3. An incomplete list of file system operations supported by NFS.

9. Tanenbaum & Van Steen, Distributed Systems: Principles and Paradigms, 2e, (c) 2007 Prentice-Hall, Inc. All rights reserved. 0-13-239227-5 9 File System Model (2) Figure 11-3. An incomplete list of file system operations supported by NFS.

10. Tanenbaum & Van Steen, Distributed Systems: Principles and Paradigms, 2e, (c) 2007 Prentice-Hall, Inc. All rights reserved. 0-13-239227-5 10 Cluster-Based Distributed File Systems (1) Figure 11-4. The difference between (a) distributing whole files across several servers and (b) striping files for parallel access.

11. Tanenbaum & Van Steen, Distributed Systems: Principles and Paradigms, 2e, (c) 2007 Prentice-Hall, Inc. All rights reserved. 0-13-239227-5 11 Cluster-Based Distributed File Systems (2) Figure 11-5. The organization of a Google cluster of servers.

12. Tanenbaum & Van Steen, Distributed Systems: Principles and Paradigms, 2e, (c) 2007 Prentice-Hall, Inc. All rights reserved. 0-13-239227-5 12 Symmetric Architectures Ivy- 1.content-hash block 2.public-key block

13. Tanenbaum & Van Steen, Distributed Systems: Principles and Paradigms, 2e, (c) 2007 Prentice-Hall, Inc. All rights reserved. 0-13-239227-5 13 Symmetric Architectures Figure 11-6. The organization of the Ivy distributed file system.

14. Tanenbaum & Van Steen, Distributed Systems: Principles and Paradigms, 2e, (c) 2007 Prentice-Hall, Inc. All rights reserved. 0-13-239227-5 14 PROCESSES stateless or stateful ?

15. Tanenbaum & Van Steen, Distributed Systems: Principles and Paradigms, 2e, (c) 2007 Prentice-Hall, Inc. All rights reserved. 0-13-239227-5 15 Remote Procedure Calls in NFS Figure 11-7. (a) Reading data from a file in NFS version 3. (b) Reading data using a compound procedure in version 4.

16. Tanenbaum & Van Steen, Distributed Systems: Principles and Paradigms, 2e, (c) 2007 Prentice-Hall, Inc. All rights reserved. 0-13-239227-5 16 The RPC2 Subsystem (1) Figure 11-8. Side effects in Coda’s RPC2 system.

17. Tanenbaum & Van Steen, Distributed Systems: Principles and Paradigms, 2e, (c) 2007 Prentice-Hall, Inc. All rights reserved. 0-13-239227-5 17 The RPC2 Subsystem (2) Figure 11-9. (a) Sending an invalidation message one at a time. (b) Sending invalidation messages in parallel.

18. Tanenbaum & Van Steen, Distributed Systems: Principles and Paradigms, 2e, (c) 2007 Prentice-Hall, Inc. All rights reserved. 0-13-239227-5 18 File-Oriented Communication in Plan 9 Figure 11-10. Files associated with a single TCP connection in Plan 9. Plan 9 is not so much a distributed file system, but rather a file-based distributed system.

19. Tanenbaum & Van Steen, Distributed Systems: Principles and Paradigms, 2e, (c) 2007 Prentice-Hall, Inc. All rights reserved. 0-13-239227-5 19 File-Oriented Communication in Plan 9 Open a telnet session - Ip address: 192.31.231.42 Port: 23 Sender writes “connect 192.31.231.42!23” to file ctl. (Receiver had written the string “announce 23” to its own ctl file.)

20. Tanenbaum & Van Steen, Distributed Systems: Principles and Paradigms, 2e, (c) 2007 Prentice-Hall, Inc. All rights reserved. 0-13-239227-5 20 Naming in NFS (1) Figure 11-11. Mounting (part of) a remote file system in NFS.

21. Tanenbaum & Van Steen, Distributed Systems: Principles and Paradigms, 2e, (c) 2007 Prentice-Hall, Inc. All rights reserved. 0-13-239227-5 21 Naming in NFS (2) Figure 11-12. Mounting nested directories from multiple servers in NFS.

22. Tanenbaum & Van Steen, Distributed Systems: Principles and Paradigms, 2e, (c) 2007 Prentice-Hall, Inc. All rights reserved. 0-13-239227-5 22 Automounting (1) Figure 11-13. A simple automounter for NFS.

23. Tanenbaum & Van Steen, Distributed Systems: Principles and Paradigms, 2e, (c) 2007 Prentice-Hall, Inc. All rights reserved. 0-13-239227-5 23 Automounting (2) Figure 11-14. Using symbolic links with automounting.

24. Tanenbaum & Van Steen, Distributed Systems: Principles and Paradigms, 2e, (c) 2007 Prentice-Hall, Inc. All rights reserved. 0-13-239227-5 24 Constructing a Global Name Space Figure 11-15. Junctions in GNS.

25. Tanenbaum & Van Steen, Distributed Systems: Principles and Paradigms, 2e, (c) 2007 Prentice-Hall, Inc. All rights reserved. 0-13-239227-5 25 Semantics of File Sharing (1) Figure 11-16. (a) On a single processor, when a read follows a write, the value returned by the read is the value just written.

26. Tanenbaum & Van Steen, Distributed Systems: Principles and Paradigms, 2e, (c) 2007 Prentice-Hall, Inc. All rights reserved. 0-13-239227-5 26 Semantics of File Sharing (2) Figure 11-16. (b) In a distributed system with caching, obsolete values may be returned.

27. Tanenbaum & Van Steen, Distributed Systems: Principles and Paradigms, 2e, (c) 2007 Prentice-Hall, Inc. All rights reserved. 0-13-239227-5 27 Semantics of File Sharing (3) Figure 11-17. Four ways of dealing with the shared files in a distributed system.