Once the load test is successful, analyzing the load test data and computing your software capacity is straight forward. Suppose you run the previous example load test and determine that two application server instances on a single server are able to handle 10,000 users each with optimum load averages on the OS (between 2 and 3). Say your server has 1 GHz processor and 1 GB of RAM, and the capacity of each server is 20,000 users. The capacity of your enterprise software is 20,000 concurrent users on a server with a 1 GHz processor with 1 GB of memory. If your application has to handle 100,000 users during peak loads, you would request five such servers, assuming unlimited availability of network bandwidth and database resources.
Knowing Your Software's Limits
Many major software vendors specify minimum OS requirements for installing their products, but how the software fares under different user loads is left for the clients to figure out. It is about time that software vendors provide load ratings for their products. The academic community is not doing any research to compute a software load-rating factor, but I have formulated my own definition: software load rating is the result of evaluating software response time in applications where the number of concurrent users on a system is the only measure of poor performance for a given server.
It is always good to compute the operating limits of your software. As the cost of memory and CPUs keeps going down, the load rating of your software keeps going up.