At what point should capacity requirements of a proposed system be first considered?

Capacity is a critical non-functional requirement that fundamentally influences a system's architecture, infrastructure, and design. According to established systems engineering and quality management principles, all requirements should be identified and analyzed as early as possible in the development lifecycle. Addressing capacity requirements during the initial planning and design phases allows for proper resource allocation, performance modeling, and architectural decisions. Deferring this consideration introduces immense risk, leading to costly rework, project delays, and potential system failure upon deployment when performance loads are applied. A proactive approach is essential for building a robust and scalable system.

A. This reactive "wait-and-see" approach is a recipe for failure, leading to costly emergency fixes and significant user dissatisfaction after implementation.
C. Identifying capacity shortfalls after development is complete necessitates major, expensive architectural changes and invalidates much of the testing already performed.
D. Discovering capacity issues just before go-live leaves no time for remediation, forcing a launch delay or guaranteeing immediate system failure.

1. Russell, J. P. (Ed.). (2020). The ASQ Certified Quality Improvement Associate Handbook (4th ed.). ASQ Quality Press. In Chapter 7, "Quality in Product and Process Design," the text emphasizes the necessity of translating customer needs into design requirements early in the process to prevent later failures. Capacity is a key technical requirement derived from customer needs (e.g., number of users, transaction volume).

2. Sommerville, I. (2011). Software Engineering (9th ed.). Pearson. In Chapter 4, "Requirements Engineering," it is stated that non-functional requirements, which include performance and capacity constraints, must be established during the requirements elicitation and analysis stage. "It is difficult to add non-functional requirements to a system late in the development process" (p. 91).

3. MIT OpenCourseWare. (2005). 6.170 Laboratory in Software Engineering, Fall 2005. Massachusetts Institute of Technology. Lecture Notes, "Lecture 2: The Software Lifecycle," emphasizes that the requirements and specification phase is the first step where both functional and non-functional properties (like performance and capacity) of the system are defined. Postponing these considerations is identified as a primary cause of project failure.