downtime
Downtime refers to the time during which a system, computer or network is unavailable to the user.
The reason for the downtime can be an error in the hardware or software that caused the downtime, but it can also be operator error or deliberate, intentional downtime, for example, to perform maintenance and repair work or to load software updates or new application software. In the case of an error, this is an unplanned downtime; in the case of maintenance, it is a planned downtime.
The classification ofavailability determines the length of downtime. This can be 48 hours per year for simple availability of 99.50% and 100% for non-stop availability.
Availability is determined by the factors Mean Time Between Failures( MTBF), which is the average time between the occurrence of two failures, and Mean Time To Repair( MTTR), which is the duration of fault clearance. High availability results from the highest possible MTBF and the lowest possible MTTR.