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Practical Monitoring by Mike Julian

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Appendix B. Availability Chart

As mentioned in Chapter 4, Table B-1 is a chart of availability numbers. It’s a great reference for how much downtime is allowed within a given availability target.

Table B-1. Availability (chart thanks to Wikipedia)
Availability % Downtime per year Downtime per month Downtime per week Downtime per day

90% (“one nine”)

36.5 days

72 hours

16.8 hours

2.4 hours

95% (“one and a half nines”)

18.25 days

36 hours

8.4 hours

1.2 hours

97%

10.96 days

21.6 hours

5.04 hours

43.2 minutes

98%

7.30 days

14.4 hours

3.36 hours

28.8 minutes

99% (“two nines”)

3.65 days

7.20 hours

1.68 hours

14.4 minutes

99.5% (“two and a half nines”)

1.83 days

3.60 hours

50.4 minutes

7.2 minutes

99.8%

17.52 hours

86.23 minutes

20.16 minutes

2.88 minutes

99.9% (“three nines”)

8.76 hours

43.8 minutes

10.1 minutes

1.44 minutes

99.95% (“three and a half nines”)

4.38 hours

21.56 minutes

5.04 minutes

43.2 seconds

99.99% (“four nines”)

52.56 minutes

4.38 minutes

1.01 minutes

8.64 seconds

99.995% (“four and a half nines”)

26.28 minutes

2.16 minutes

30.24 seconds

4.32 seconds

99.999% (“five nines”)

5.26 minutes

25.9 seconds

6.05 seconds

864.3 milliseconds

99.9999% (“six nines”)

31.5 seconds

2.59 seconds

604.8 milliseconds

86.4 milliseconds

99.99999% (“seven nines”)

3.15 seconds

262.97 milliseconds

60.48 milliseconds

8.64 milliseconds

99.999999% (“eight nines”)

315.569 milliseconds

26.297 milliseconds

6.048 milliseconds

0.864 milliseconds

99.9999999% (“nine ...

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