Every administrator should know the performance of the servers and services he is responsible for. Normally the performance of services if measured in actions per time. For instance for a database this would be accesses or inserts per second, for a webserver sites delivered per second. For a mailserver this figure are messages handled per second.
Of course every admin can estimate the performance of his servers. But measuring is always better the guessing. Measuring things on productive live systems is the task of a monitoring systems.
In this article I want to present a method to measure the performance of live systems in real time. This results in much more accurate values than any educated guess. I will demonstrate my method with a mail server, but the method can be applied to any service. You just have to measure the throughtput and CPU usage and combine both values with some simple math.