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Reliability Percentages and what they mean


Many people are thoroughly confused by reliability percentages; so here is a little table explaining what these numbers actually say.

Given that we make statements about a system that has a planned availability of 24 hours a day 365 days a year, the following applies:

Reliability

Outage per year

90%

36 days and 12 hours

95%

18 days and 3 hours

98%

7 days and 8 hours

99%

3 days, 15 hours and 36 minutes

99.9%

8 hours, 45 minutes and 36 seconds

99.99%

52 minutes and 34 seconds

99.999%

5 minutes and 15 seconds

99.9999%

32 seconds

99.99999%

3 seconds


It is easy to see that very high reliability figures are extremely hard to reach. So, be careful with what you promise in your SLA!

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Page History :: 2009-03-31 17:35:14 XML :: Owner: Roland Stens :: Search:
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