Capacity planning is done before resources run out, not when they have already run out. In most organisations capacity comes to the agenda through a message like “the disk is full” or “the server is slow”, after an incident. With regular usage data collection, the bottleneck is visible months earlier.
The metrics that matter
Different resource types need different metrics. CPU percentage alone is not a sufficient indicator; process wait time and the run queue give an earlier warning. For memory, commit usage and page fault rates are more telling than usage percentage. On the storage side, IOPS latency and queue depth have to be tracked next to capacity.
- CPU: Average usage, peak usage, process wait time
- RAM: Commit usage, cache hit ratio, page faults
- Storage: Capacity usage, IOPS latency, queue depth
- Network: Bandwidth, packet loss, latency and jitter
Peak hours and seasonality
Averages are misleading in capacity planning. A system with a comfortable annual average can still be pushed to ninety percent during a month-end close. The capacity plan has to account for peak hours and seasonal shifts. In e-commerce and production environments, resource demand changes significantly during the year.
Growth scenarios
A plan should not rely on a single forecast. Working with three scenarios produces a more reliable result.
- No growth: Current usage covered by horizontal investment.
- Planned growth: Annual growth of twenty to thirty percent in line with business targets.
- Unexpected growth: A new project, a new branch or the effect of an acquisition.
Scaling options
When a bottleneck is found, the options have to be evaluated in order: add resources, balance the workload, optimise the application and change the architecture. Horizontal scaling is not always the right answer. If a single database server cannot be scaled horizontally, the architectural options have to be evaluated first.
Turn the plan into a living document
A capacity plan should not be a table that is prepared once a year and then forgotten. With metrics, thresholds, owners and the investment items to be executed, it has to be a document that stays alive. The Serventa infrastructure calculator uses your current usage data to produce a first draft of that plan.
