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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