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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