Downtime
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Downtime refers to a period of time or a percentage of a timespan that a machine or system (usually a computer server) is offline or not functioning, usually as a result of either system failure (such as a crash) or routine maintenance. The opposite is uptime.
- Maintenance Downtimes have to be carefully scheduled in industries that rely on nearly 24-hour service, such as e-commerce, medical, news reporting, and persistent online games.
- Downtimes caused by system failures can have serious economic impact. To minimize these effects network monitoring should be used.
In Service Level Agreements it is common to mention a percentage value (per month or per year) that is calculated by dividing the sum of all downtimes timespans by the total time of a reference time span (e.g. a month). 0% downtime means that the server was available all the time.
For Internet servers downtimes above 1% per year or worse can be regarded as unacceptable as this means a downtime of more than 3 days per year. For e-commerce and other industrial use any value above 0.1% is unacceptable.