Capacity Planning versus Scalability

Scalability defines a system’s ability to utilize additional resources to meet user demand. In contrast, capacity planning defines the resources your application will need at a specific time. The two terms are related, yet different. When your first design a system, for example, you might plan for 10,000 users accessing the system between 6:00 a.m. and 6:00 p.m. Starting with your user count, you can then begin to determine the number of servers needed, the bandwidth requirements, the needed disk space, and so on. In other words, the capacity your system will need to operate.

When your user demand exceeds your system capacity, you must then scale the system by adding resources.