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In short: uptime is the share of time a service is reachable, measured over a month or a year and written as a percentage. 99.9% sounds close to 99%, but the difference is 3.2 days of downtime a year versus 8.8 hours.
Uptime depends on what you measure
The same question means different things depending on who you ask. A data centre selling network capacity measures the availability of the network. A hosting company measures whether the web server software answers requests. A site owner cares about whether the whole page, with all its images and scripts, loads for visitors. When you compare uptime promises, ask which of these the figure refers to.
Uptime is written into an SLA (service level agreement) as a percentage of the measurement period. The table below shows how much downtime each common figure allows.
| Uptime | Downtime per year | Per month | Per week |
|---|---|---|---|
| 90% ("one nine") | 36.5 days | 72 hours | 16.8 hours |
| 95% | 18.25 days | 36 hours | 8.4 hours |
| 98% | 7.3 days | 14.4 hours | 3.4 hours |
| 99% ("two nines") | 3.65 days | 7.2 hours | 1.7 hours |
| 99.5% | 1.83 days | 3.6 hours | 50 minutes |
| 99.9% ("three nines") | 8.76 hours | 43 minutes | 10 minutes |
| 99.95% | 4.38 hours | 21.6 minutes | 5 minutes |
| 99.99% ("four nines") | 52.6 minutes | 4.3 minutes | 1 minute |
| 99.999% ("five nines") | 5.3 minutes | 26 seconds | 6 seconds |
How to measure your own uptime
Do not rely on the provider's figure alone. An external monitor that requests your site every minute from several locations (HetrixTools, UptimeRobot and similar services have free tiers) gives you an independent record and alerts you when the site stops answering. Monitor the real page, not just a ping to the server: a server can answer ping while the web service is down.
Fiberserver's uptime
We tell every customer who asks that we commit to above 90%, and in the yearly tests and monitors we run the measured figure is around 99.7%, with some hosting servers above that. No provider in Türkiye or abroad can honestly promise that an outage will never happen; what matters is how short and how rare they are, and whether you hear about them before your visitors do.
What to check in an SLA
- Which service the percentage covers: network, server or application.
- The measurement period: a monthly figure hides less than a yearly one.
- Whether scheduled maintenance counts as downtime.
- What compensation applies when the figure is missed.
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