Systematic measurements of server performance employing adequate resolution typically produce a graph shaped like the one shown in Figure 140 on page 169. The characteristics that shape this graph are important for understanding potential bottlenecks in a file server.
Figure 140. File Server Performance - General Characteristics
The horizontal axis shows the number of simultaneous active users. The vertical axis indicates server throughput, or number of transactions per second. This is the total number of transactions per second at the server, rather than the individual transaction rate for each workstation.
For the purpose of measuring throughput, a transaction can be an arbitrary unit of work. However, it is more meaningful to consider a transaction to be a typical user task. For example, a transaction can be defined as a networked client loading a spreadsheet, processing it at the workstation and then saving it back to the server. This process can be executed by a large number of workstations attached to a single file server to determine the maximum number of
Note
It is important to note that the number of transactions per second will be greatly dependent upon the transaction definition. Obviously, a one page document
Figure 140 shows a graph of file server performance where throughput initially increases at a constant rate as users are added to the server. As the total number of users is increased, the network operating system is able to maintain a sufficiently high disk cache hit rate. Most user I/O requests are being serviced directly from the cache. The curve continues to climb until it reaches a peak,
Chapter 5. Performance Tuning 169
