4.3Capacity management (demand forecasting, thresholds, trend analysis)

Capacity management is not a reactive task of "augment once performance runs short." Avoiding both over-investment (holding too much unused equipment) and under-investment (SLA breaches from insufficient performance), its essence is to read demand growth ahead of time and secure exactly the capacity needed, when needed, most cost-effectively. This section organizes what is managed via three sub-processes and builds the judgment to catch signs of shortfall at the early-warning stage through threshold monitoring and trend analysis, and to decide whether to augment or to level demand through demand management.

4.3.1The three sub-processes

• Business capacity management is the most upstream sub-process, forecasting mid-to-long-term required capacity from the business plan and future business demand (planned new services, expected user growth, etc.). Service capacity management monitors and manages end-to-end performance per individual service to meet SLA performance targets (response time, throughput, etc.). Component capacity management is the most downstream sub-process, monitoring and managing the utilization of individual resources (components) such as CPU, memory, disk, and line bandwidth.
• The three sub-processes connect from upstream to downstream: "business -> service -> component." Looking only at a single component's utilization cannot tell you how it affects the SLA (service performance) or business growth—for example, rising CPU utilization does not immediately require augmentation if it is not affecting the SLA response time. Conversely, if the business plan foresees a large user increase, an augmentation plan is drawn up ahead of time even with current headroom. Judging by cross-referencing the three viewpoints is the crux of capacity management.