SLI - Service Level Indicator
Defines a measure of service level provided by service providers.
Examples
- Uptime of the service
- Number of Transactions
SLO - Service Level Objective
Defines a target value or a target range of service level, measured by SLI.
Examples
- Availability of the service should be 99.999%
SLA - Service Level Agreement
Defines a commitment between service providers and customers.
Examples
- Refund service fee
- Provide free service for a period of time
The Nines
Percentages to measure the service.
| Availability % | Downtime per year | Downtime per month | Downtime per week | Downtime per day |
|---|---|---|---|---|
| 55.5555555% ("nine fives") | 162.33 days | 13.53 days | 74.92 hours | 10.67 hours |
| 90% ("one nine") | 36.53 days | 73.05 hours | 16.80 hours | 2.40 hours |
| 95% ("one nine five") | 18.26 days | 36.53 hours | 8.40 hours | 1.20 hours |
| 97% | 10.96 days | 21.92 hours | 5.04 hours | 43.20 minutes |
| 98% | 7.31 days | 14.61 hours | 3.36 hours | 28.80 minutes |
| 99% ("two nines") | 3.65 days | 7.31 hours | 1.68 hours | 14.40 minutes |
| 99.5% ("two nines five") | 1.83 days | 3.65 hours | 50.40 minutes | 7.20 minutes |
| 99.8% | 17.53 hours | 87.66 minutes | 20.16 minutes | 2.88 minutes |
| 99.9% ("three nines") | 8.77 hours | 43.83 minutes | 10.08 minutes | 1.44 minutes |
| 99.95% ("three nines five") | 4.38 hours | 21.92 minutes | 5.04 minutes | 43.20 seconds |
| 99.99% ("four nines") | 52.60 minutes | 4.38 minutes | 1.01 minutes | 8.64 seconds |
| 99.995% ("four nines five") | 26.30 minutes | 2.19 minutes | 30.24 seconds | 4.32 seconds |
| 99.999% ("five nines") | 5.26 minutes | 26.30 seconds | 6.05 seconds | 864.00 milliseconds |
| 99.9999% ("six nines") | 31.56 seconds | 2.63 seconds | 604.80 milliseconds | 86.40 milliseconds |
| 99.99999% ("seven nines") | 3.16 seconds | 262.98 milliseconds | 60.48 milliseconds | 8.64 milliseconds |
| 99.999999% ("eight nines") | 315.58 milliseconds | 26.30 milliseconds | 6.05 milliseconds | 864.00 microseconds |
| 99.9999999% ("nine nines") | 31.56 milliseconds | 2.63 milliseconds | 604.80 microseconds | 86.40 microseconds |
Source: Wiki
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