Five Nines refers to 99.999% availability, meaning a system is expected to be unavailable for only about five minutes over a full year. It is a common shorthand benchmark for very high reliability in data-center and telecom services. Each additional nine is exponentially harder and costlier to achieve, so the target is matched to the criticality of the workload.
Category: Colocation & Cloud Services · Subcategory: Service Levels · Part of the AIDC Technical Terminology reference.