uptime

Uptime describes how long a system works and remains reachable. For websites and online services, it often measures availability over a month or year. Uptime of 100 percent means the service was available throughout the measurement period.

How is uptime calculated?

Divide the available time by the total measurement time and multiply by 100. Over a thirty-day month, 99.9 percent uptime corresponds to roughly 43 minutes of downtime.

The calculation seems simple, but its underlying agreements matter. An SLAGlossary · In briefSLASLA stands for service level agreement: an agreement between a customer and provider about the service, its agreed level and how that level is measured.Read more can specify whether planned maintenance counts, when an incident starts and which service components are covered. Two providers can quote the same percentage while measuring different things.

How does uptime differ from downtime?

DowntimeGlossary · In briefdowntimeDowntime is the period when software, a system or an online service is unavailable or its essential functions cannot be used.Read more is the period when a system is unavailable or unusable. Uptime and downtime complement one another within the same measurement period. Thus, 99.9 percent uptime corresponds to 0.1 percent downtime when both use the same definition and method.

MonitoringGlossary · In briefmonitoringMonitoring systematically tracks software, infrastructure or processes through measurements and checks. Deviations can trigger alerts so an administrator can investigate.Read more checks whether a service responds and can provide uptime measurements. A check from one location does not always prove every user can reach the service. A network route problem or failing feature may affect some users while the general check still passes. Organizations therefore define what they measure, from which locations and at which intervals.