Availability is the proportion of time a system is able to perform its function. It is usually written as a percentage: time the service was up divided by total time in the measurement window.
Why it matters
Availability is the headline number in most SLAs और SLOs, so small decimal differences carry large operational meaning. The window matters as much as the number: 99.9 percent allows about 43 minutes of downtime in a 30-day month, but also about 8.8 hours across a year.
Example
availability = (total time - downtime) / total time
30-day month = 43,200 minutes
downtime = 52 minutes
availability = (43,200 - 52) / 43,200 = 99.88%Rough yearly allowances: 99 percent is about 3.65 days, 99.9 percent about 8.8 hours, and 99.99 percent about 53 minutes. For how to read these figures, see the guide on uptime percentages.
Request-based availability is a common alternative: successful requests divided by total requests. It reflects partial outages better than a simple up/down clock.
Common mistakes
- Counting only full outages and ignoring slow or partially failing periods that users experience as down.
- Excluding planned maintenance without saying so.
- Measuring from inside your own network, which misses DNS, CDN, and ISP problems.
- Confusing it with reliability, which includes correctness over time.
Related
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यह पेज सामान्य जानकारी है, जिसे हमारी संपादकीय टीम ने लिखा है और दस्तावेज़ीकरण बदलने पर अपडेट किया जाता है। सर्वर और प्रदाता अलग-अलग होते हैं, इसलिए बदलाव पहले सुरक्षित तरीके से जाँचें। देखें: संपादकीय नीति और अस्वीकरण.