IBM eServer Certification Study Guide: Cluster 1600 Managed by PSSP

Chapter 4. I/O devices and file systems 155

Time Service DFS uses the DCE Distributed Time Service. AFS clients

use their cache manager and NTP to synchronize with the

AFS servers.

Synchronization Both DFS and AFS use a token manager to coordinate

concurrent access to the file system. However, AFS

revokes tokens from other clients when closing a file;

whereas, DFS already revokes the token when opening

the file. This means that DFS semantics are completely

conforming with local file system semantics, whereas,

AFS semantics are not. Nevertheless, AFS

synchronization is better than in NFS, which does not use

tokens at all.

It is obvious that DFS is well integrated with the other DCE core services;

whereas, AFS requires more configuration and administration work. DFS also

provides file system semantics that are superior to AFS. So, unless an existing

AFS cell is expanded, we recommend that DFS is used rather than AFS to

provide global file services.

4.5 Related documentation

This documentation will help you better understand the concepts and examples

covered in this chapter. We recommend that you take a look at some of these

books in order to maximize your chances of success in the SP certification exam.

SP manuals

RS/6000 SP Planning, Volume 2: Control Workstation and Software

Environment, GA22-7281. This manual gives detailed explanations on I/O

devices.

RS/6000 SP: Planning, Volume 1, Hardware and Physical Environment,

GA22-7280. This book is the official document for supported I/O adapters.

SP redbooks

Inside the RS/6000 SP, SG24-5145. NFS and AFS concepts are discussed in

this redbook.

IBM (e)server Cluster 1600 Managed by PSSP 3.5: What’s New, SG24-6617.