Understanding the levels of IT service
Availability is directly tied with service level and is normally defined as a percentage. It is the percentage of uptime over a defined period. The availability that you can guarantee is your service level. The following table shows what exactly this means by considering the maximum admitted downtime for a few of the frequently used availability percentages:
|
Availability percentage |
Max downtime per year |
Max downtime per month |
Max downtime per week |
|---|---|---|---|
|
90% called one nine |
36.5 days |
72 hours |
16.8 hours |
|
95% |
18.25 days |
36 hours |
8.4 hours |
|
99% called two nines |
3.65 days |
7.20 hours |
1.68 hours |
|
99.5% |
1.83 days |
3.60 hours |
50.4 minutes |
|
99.9% called three nines |
8.76 hours |
43.8 minutes |
10.1 minutes |
|
99.95% |
4.38 hours |
21.56 minutes |
5.04 minutes |
|
99.99% called four nines |
52.56 minutes |
4.32 minutes |
1.01 minutes |
|
99.999% called five nines |
5.26 minutes |
25.9 seconds |
6.05 seconds |
|
99.9999% called six nines |
31.5 seconds |
2.59 seconds | ... |
