Let’s really shoot ourselves in the foot.

There was a discussion at work the other week about system availability measurements.  We’re aiming for “Five Nines”.  Noble target, doubt we’ll achieve it though, without some clever availability exclusions.  I’ve mentioned those exclusions before.

Availability %

Downtime per week Downtime per month* Downtime per year

90%

16.8 hours 72 hours 36.5 days

95%

8.4 hours 36 hours 18.25 days

98%

3.36 hours 14.4 hours 7.30 days

99%

1.68 hours 7.20 hours 3.65 days

99.50%

50.4 minutes 3.60 hours 1.83 days

99.80%

20.16 minutes 86.23 minutes 17.52 hours

99.9% (“three nines”)

10.1 minutes 43.2 minutes 8.76 hours

99.95%

5.04 minutes 21.56 minutes 4.38 hours

99.99% (“four nines”)

1.01 minutes 4.32 minutes 52.6 minutes

99.999% (“five nines”)

6.05 seconds 25.9 seconds 5.26 minutes

99.9999% (“six nines”)

0.605 seconds 2.59 seconds 31.5 seconds

Table courtesy of Wikipedia – High Availability.
* For monthly calculations, a 30-day month is used.

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