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# Availability Calculator
- **期号**: SRE Weekly Issue #84（2017-08-06）
- **作者**: —
- **链接**: https://dastergon.github.io/availability-calculator/
## 简介
How many minutes per month is 99.95% availability? What about 99.957%? Here’s a tool that’ll give you a quick answer, by the author of awesome-sre.
## 正文
"In general, for any software service or system you can think of, 100% is not the right
reliability
target
because no user can tell the difference between a system being 100% available and, let's say,
99.999%
available." - [Ben
Treynor](https://landing.google.com/sre/interview/ben-treynor.html)
| Availability level | Downtime per year | Downtime per quarter | Downtime per month | Downtime per week | Downtime per day | Downtime per hour |
|---|---|---|---|---|---|---|
| 90% | 36.52 days | 9.13 days | 3.04 days | 16.80 hours | 2.40 hours | 6.00 minutes |
| 95% | 18.26 days | 4.57 days | 1.52 days | 8.40 hours | 1.20 hours | 3.00 minutes |
| 99% | 3.65 days | 21.91 hours | 7.30 hours | 1.68 hours | 14.40 minutes | 36.00 seconds |
| 99.5% | 1.83 days | 10.96 hours | 3.65 hours | 50.40 minutes | 7.20 minutes | 18.00 seconds |
| 99.9% | 8.77 hours | 2.19 hours | 43.83 minutes | 10.08 minutes | 1.44 minutes | 3.60 seconds |
| 99.95% | 4.38 hours | 1.10 hours | 21.91 minutes | 5.04 minutes | 43.20 seconds | 1.80 seconds |
| 99.99% | 52.59 minutes | 13.15 minutes | 4.38 minutes | 1.01 minutes | 8.64 seconds | 0.36 seconds |
| 99.999% | 5.26 minutes | 1.31 minutes | 26.30 seconds | 6.05 seconds | 0.86 seconds | 0.04 seconds |