4.1 Introduction

Here is a central question: how can one plan, design, develop, deploy and operate IT services that meet the ever increasing demands for performance, availability, reliability, security, and cost? Or, being more specific, is a given IT system properly designed and sized for a given load condition? Can the insurance claims management system meet the performance requirement of subsecond response time? Is the infrastructure of a government agency scalable and can it cope with the new online security policies required for financial transactions? Can the security mechanisms be implemented without sacrificing user-perceived performance? Is the reservations system for cruise lines able to respond to the anticipated peak of consumer inquiries that occurs after a TV advertisement campaign?

By breaking down the complexity of an IT system, one can analyze the functionality of each component, evaluate service requirements, and design and operate systems that will meet user's expectations. In other words, the answer to the above questions requires a deep understanding of the system architecture and its infrastructure. This chapter presents the basic steps of a methodology for performance engineering that are needed to fulfill the major performance needs of IT services.