IBM SG24-4576-00 manual Differences in LAN Adapters

Figure 141. Differences in LAN Adapters

Upgrading the disk subsystem will tend to flatten out the top of the curve as it will provide a higher sustainable data transfer rate. In most cases, the disk subsystem becomes the bottleneck when a large number of users becomes active. Since most disk subsystems are significantly slower than a cache-hit operation, the throughput curve begins to decline. High performance disk subsystems, such as an IBM RAID Controller with Fast SCSI-2 drives, offer such a high level of performance that for many applications it allows the peak transaction rate to be sustained indefinitely. The general shape of the curve will be similar to the one shown in Figure 142 on page 172. Where the peak performance in transactions per second occurs, the line will continue horizontally rather than dipping as it would when the bottleneck is the disk subsystem. That is, for this workload the disk subsystem is no longer the system bottleneck and the peak transaction rate is sustained.

Chapter 5. Performance Tuning 171