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Performance Test Environment

In general, the more closely the performance test environment reflects the production environment, the more applicable the test results will be. It is important that the performance test environment includes all of the relevant components to test all aspects of the system, including integration and third-party components. Often it is not feasible to build a full duplicate of the production configuration for testing purposes. In that case, the following scaled-down strategy should be employed for each tier:

• Web Servers and Siebel Servers. To scale down the Web and application server tiers, the individual servers should be maintained in the production configuration and the number of servers scaled down proportionately. The overall performance of a server depends on a number of factors besides the number of CPUs, CPU speed, and memory size. So, it is generally not accurate to try to map the capacity of one server to another even within a single vendor's product line.

  The primary tier of interest from an application scalability perspective is the application server tier. Scalability issues are very rarely found on the Web server tier. If further scale-down is required it is reasonable to maintain a single Web server and continue to scale the application server tier down to a single server. The application server should still be of the same configuration as those used in the production environment, so that the tuning activity can be accurately reflected in the system test and production environments.

• Database server. If you want to scale down a database server, there is generally little alternative but to use a system as close as possible to the production architecture, but with CPU, memory, and I/O resources scaled down as appropriate.
• Network. The network configuration is one area in which it is particularly difficult to replicate the same topology and performance characteristics that exist in the production environment. It is important that the system test includes any active network devices such as proxy servers and firewalls. The nature of these devices can impact not only the performance of the system, but also the functionality, because in some cases these devices manipulate the content that passes through them. The performance of the network can often be simulated using bandwidth and latency simulation tools, which are generally available from third-party vendors.