99.5% uptime: how much downtime is that?
99.5% uptime allows 7 minutes 12 seconds of downtime a day, 3 hours 39 minutes in an average month and 1 day 19 hours 48 minutes a year. It halves the budget of 99% and is the point where outages at night start to matter.
Downtime allowed by 99.5% uptime
| Period | Allowed downtime |
|---|---|
| Daily | 7m 12s |
| Weekly | 50m 24s |
| Monthly | 3h 39m |
| Quarterly | 10h 57m |
| Yearly | 1d 19h 48m |
| 30-day month | 3h 36m |
| 31-day month | 3h 43m 12s |
| 28-day month | 3h 21m 36s |
A month is the average month, a twelfth of a 365-day year; a quarter is a quarter of it.
What that looks like
One long incident a month fits, as long as it stays under about three and a half hours. An outage that waits for the morning does not.
Over a year the budget is a little under two days, so one bad weekend can use all of it.
How many outages fit
| One outage of | Per month | Per year |
|---|---|---|
| 1m | 219 | 2628 |
| 5m | 43 | 525 |
| 15m | 14 | 175 |
| 30m | 7 | 87 |
| 1h | 3 | 43 |
| 4h | 0 | 10 |
Counts whole outages of that length that fit in the budget of an average month or a year, with nothing else going wrong.
What 99.5% takes
- Alerts that reach someone outside working hours, even if the response is best effort.
- Automatic restarts and health checks, so the common failures fix themselves.
- Announced maintenance windows, or updates that do not take the service offline.
- Checks every few minutes, so an outage is noticed while there is budget left.
Where it fits: Early-stage products, business tools used mostly during office hours and client sites run by a small agency.
How to measure it
Check at most every tenth of the budget, so short outages do not slip between checks: every 21m 54s or more often for a monthly 99.5%. In OpenUptime that is any plan, including Free (every 5 minutes).
Check from more than one region, so a single network problem between one location and your server is not counted as downtime.
Compared with other targets
| Uptime | Monthly | Yearly | Downtime against 99.5% |
|---|---|---|---|
| 99% | 7h 18m | 3d 15h 36m | 2× as much |
| 99.5% | 3h 39m | 1d 19h 48m | this page |
| 99.9% | 43m 48s | 8h 45m 36s | 1/5 as much |
| 99.95% | 21m 54s | 4h 22m 48s | 1/10 as much |
| 99.99% | 4m 23s | 52m 34s | 1/50 as much |
| 99.999% | 26.3s | 5m 15s | 1/500 as much |
Track 99.5% uptime
OpenUptime records every check, shows uptime per monitor and on 90-day status page bars, and alerts you when a check fails.
Questions
How much downtime is 99.5% per month?
About 3 hours 39 minutes in an average month, 3 hours 36 minutes in a 30-day month and 3 hours 43 minutes in a 31-day month.
Is 99.5% enough for an online shop?
It depends on when the downtime falls. Three hours at 3 a.m. may cost little; the same three hours during a sale costs much more. Monitor the checkout, not only the home page.
What is the difference between 99.5% and 99.9%?
Five times the downtime: 3 hours 39 minutes a month against 43 minutes 48 seconds.
99.5% 可用率意味着多少停机时间？
99.5% 可用率每天允许 7 分 12 秒停机，平均每月 3 小时 39 分，每年 1 天 19 小时 48 分。它的预算是 99% 的一半，从这里开始，夜间的故障就不能放到第二天再处理了。
99.5% 可用率允许的停机时间
| 周期 | 允许的停机时间 |
|---|---|
| 每天 | 7 分 12 秒 |
| 每周 | 50 分 24 秒 |
| 每月 | 3 小时 39 分 |
| 每季度 | 10 小时 57 分 |
| 每年 | 1 天 19 小时 48 分 |
| 30 天 | 3 小时 36 分 |
| 31 天 | 3 小时 43 分 12 秒 |
| 28 天 | 3 小时 21 分 36 秒 |
一个月指平均月，即 365 天的十二分之一；一个季度是一年的四分之一。
实际意味着什么
每月可以容纳一次较长的故障，只要不超过三个半小时左右。等到第二天早上再处理的故障就超出了。
一年的预算不到两天，一个糟糕的周末就可能全部用完。
预算能容纳几次故障
| 单次故障时长 | 每月 | 每年 |
|---|---|---|
| 1 分 | 219 | 2628 |
| 5 分 | 43 | 525 |
| 15 分 | 14 | 175 |
| 30 分 | 7 | 87 |
| 1 小时 | 3 | 43 |
| 4 小时 | 0 | 10 |
表示在平均月或一年的预算内，能容纳多少次这样时长的完整故障（假设没有其他问题）。
做到 99.5% 需要什么
- 告警在工作时间之外也能通知到人，即使只是尽力响应。
- 自动重启和健康检查，让常见故障能自行恢复。
- 提前公告的维护窗口，或者不需要让服务下线的更新方式。
- 每隔几分钟检查一次，在预算还没用完时就发现故障。
适用场景： 早期产品、主要在工作时间使用的业务工具，以及小型代理机构维护的客户网站。
怎样测量
检查间隔不要超过预算的十分之一，以免短暂的故障落在两次检查之间：按月计算的 99.5%，检查间隔应不超过 21 分 54 秒。在 OpenUptime 中，这对应 任何套餐，包括 Free（每 5 分钟）。
从多个区域检查，这样某一个地点到服务器之间的网络问题就不会被算作停机。
与其他目标对比
| 可用率 | 每月 | 每年 | 停机时间与 99.5% 相比 |
|---|---|---|---|
| 99% | 7 小时 18 分 | 3 天 15 小时 36 分 | 2 倍 |
| 99.5% | 3 小时 39 分 | 1 天 19 小时 48 分 | 本页 |
| 99.9% | 43 分 48 秒 | 8 小时 45 分 36 秒 | 1/5 |
| 99.95% | 21 分 54 秒 | 4 小时 22 分 48 秒 | 1/10 |
| 99.99% | 4 分 23 秒 | 52 分 34 秒 | 1/50 |
| 99.999% | 26.3 秒 | 5 分 15 秒 | 1/500 |
常见问题
99.5% 每月允许多少停机？
平均月约 3 小时 39 分，30 天的月 3 小时 36 分，31 天的月 3 小时 43 分。
99.5% 对网店来说够吗？
取决于停机发生在什么时候。凌晨 3 点停三个小时可能影响不大，促销期间停三个小时损失就大得多。要监控结账流程，而不只是首页。
99.5% 和 99.9% 差多少？
停机时间相差五倍：每月 3 小时 39 分，对比 43 分 48 秒。