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.