Concept · measure · registered

Availability

The proportion of good events among valid events in a stated window, for the availability indicator the service uses. ITIL uses availability for the ability of a service to perform its agreed function when required. This concept is a measurement of that ability, not the ability itself and not a target. The SRE book defines it as the fraction of time a service is usable, and often implements that fraction as the yield of well-formed requests. Those two proportions answer different questions and must not be mixed in one figure. A duration of uptime is not this proportion. The proportion is not a service level objective and not a service level agreement.