Without a way to measure current capacity you can't plan — you're guessing. But don't agonize over which tool. For capacity planning a measurement tool needs, at minimum, to: - record and store data over time, - build custom metrics, - compare metrics from various sources, - import and export metrics. Any tool that satisfies these works (Cacti, Munin, Ganglia, Hyperic — Allspaw sometimes just used Excel). What matters far more than the brand is **what metrics you choose to measure and which you pay attention to**. A scope caveat: in web ops "monitoring" conflates alerting (Nagios-style smoke detectors) with metric collection (a court reporter that records without acting). Capacity work needs the *collection* kind — store and display system + application metrics over time — not the notification kind. --- *Source: [[The Art of Capacity Planning]] (John Allspaw, O'Reilly 2008) — Ch 3 — Measurement: Units of Capacity*