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.
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 nines”) |
31.5569 milliseconds |
2.6297 milliseconds |
0.6048 milliseconds |
0.0864 milliseconds |
3.17.162.214