1. 11.3 Distributed File Systems Communication
Xueli Xiao

2. Communication
Usually based on remote procedure calls, or some variation.
Rationale for choosing RPC mechanism: To make the system independent from underlying operating systems, networks and transport protocols.
RPCs in NFS
RPC2 Subsystem
File-Oriented Communication in Plan 9

3. What is RPC (remote procedure call)
Remote Procedure Call (RPC) is a protocol that one program can use to request a service from a program located in another computer in a network without having to understand network details.

4. What is NFS
• Network file system
• Client-server architecture

5. RPCs in NFS
• Before NFSv4: Each file system operation is represented as an RPC. Pre- version 4 NFS required one RPC at a time, so server didn’t have to remember any state.
• NFSv4: supports compound procedures (several RPCs grouped together)

6. RPCs in NFS
Reading data from a file in NFS version Reading data using compound procedure in version 4

7. RPC2 Subsystem • An enhancement to RPCs • Support for side effects
• Support for multicasting

8. RPC2 Subsystem Side effect
A side effect is a mechanism by which the client and server can communicate using an application-specific protocol.

9. RPC2 Subsystem
Side effects in Coda’s RPC2 System

10. RPC2 Subsystem Multicasting
Multicast is group communication where information is addressed to a group of destination computers simultaneously.

11. RPC2 Subsystem
Sending invalidation message one at a time Sending invalidation message in parallel

12. File-Oriented Communication in Plan 9
• Plan 9: a file-based distributed system originally developed by the Bell Labs
• File-oriented communication: a completely different approach to handling communication
• Network interfaces are represented by a file system, in this case consisting of a collection of special files.
• Example: an individual TCP connection is represented by a subdirectory consisting of relevant files.

13. File-Oriented Communication in Plan 9
Files associated with a single TCP connection in Plan 9

14. File-Oriented Communication in Plan 9
• Used to send control commands to the connection
• Example: Open a telnet session to a machine with IP address using port 23
requires the sender to write the text string “connect !23” to file ctl
receiver have previously written “announce 23” to its own ctl file

15. File-Oriented Communication in Plan 9
• Used to exchange data by simply performing read and write operations
• These operations follow the usual UNIX semantics for file operations
• Example: write data to a connection
res - write(fd, buf, nbytes)

16. Current Communication Mechanisms

17. Future Research Energy-efficient communication
fault-tolerant data communication system
Use of RPCs in high performance computing

18. References Distributed systems principles and paradigms
Thanh, T.D.; Mohan, S.; Eunmi Choi; SangBum Kim; Pilsung Kim, "A Taxonomy and Survey on Distributed File Systems," in Networked Computing and Advanced Information Management, NCM '08. Fourth International Conference on , vol.1, no., pp , 2-4 Sept. 2008

19. Thank you!