This section discusses some issues that often arise when configuring a WCAT test environment. It also recommends hardware and software configurations that are likely to provide accurate, repeatable results from most WCAT tests. These include:
· The optimal amount of physical memory for the WCAT server.
· The best network configuration for a WCAT test.
· The recommended number of virtual clients for a WCAT test.
To determine the most appropriate configuration for your system, repeat several different WCAT tests under different conditions. Vary the speed and number of processors, the amount of physical memory, the available hard disk space and disk configuration, and network bandwidth and traffic. Also, vary the number and speed of the client computers and the number of virtual clients run on each client computer. Repeat the tests to eliminate any one-time performance limitations that are not specific to the WCAT tests.
The amount of physical memory in your server computer can limit the performance of your Internet Information Server and cause excessive disk operations. Unless you are testing how different amounts of memory affect the performance of your server, make sure that your system has sufficient memory for your configuration. It is recommended that the Internet Information Server should have enough physical memory to contain all static content pages involved in the test simultaneously.
For more information on the physical memory requirements of an Internet Information Server, see Supplement 1, Chapter 5, “Monitoring Virtual Memory.”
A network with limited bandwidth or substantial traffic might limit the performance of your server. Depending on your goals for the WCAT tests, you can include a network with limited bandwidth or provide ideal network conditions so the network is not a factor in the test.
To provide ideal network conditions, dedicate a network to the WCAT tests.
If a limited bandwidth is part of your test, there is no single set of recommended bandwidth requirements for the WCAT tests. In this case, you might want to simulate a busy or limited network. To simulate different network conditions, you can use the IIS Bandwidth Throttler to change the bandwidth available to Internet Information Server. For more information about the Bandwidth Throttler, see “Limiting Bandwidth” in Supplement 1, Chapter 7, “Monitoring Bandwidth and Network Capacity.”
You can use WCAT to simulate varying client conditions. You can vary the number of client computers in the test, the number of virtual clients running on each client computer, and the rate at which the clients send requests to the server.
To determine the maximum load the server can handle, it is recommended that you use four or more client machines, each running three or more virtual clients, in your WCAT tests. The processors in the client computers should be at least as fast as the processors in the server computer. If the client processors are not as fast as the server processors, more client computers should be associated with each server computer.