- Agreement between the service provider and its customer formally defining the level of uptime the service will deliver
- Uptimes are generally measured in nines. The more the nines, the better.
- For example, a service guaranteeing 99.999% of uptime has 3 nines.
99.99% is not enough
| Availability % | Downtime per day | Downtime per week | Downtime per month | Downtime per year |
|---|
| 99% | 14.40 minutes | 1.68 hours | 7.31 hours | 3.65 days |
| 99.99% | 8.64 seconds | 1.01 minutes | 4.38 minutes | 52.60 minutes |
| 99.999% | 864.00 | 6.05 seconds | 26.30 seconds | 5.26 minutes |
| 99.9999% | 86.40 milliseconds | 604.80 milliseconds | 2.63 seconds | 31.56 seconds |
Sources