Availability

How long is a system working? This means functional and responding.

It’s common to measure it as a percentage:

System Availability

% of UptimeDaily DowntimeWeekly downtimeMonthly downtimeYearly downtime
9914m:24s1h:40m:487h:8m:17s3d:15h:39m
99.9 aka 3 Nines1m26s10m4.8s43m49.78h45m57
99.9543s5m2.4s21m54s4h22m58s
99.99 aka 4 Nines8.6s1m0.5s4m23s52m35.7s
99.999 aka 5 Nines aka Very Expensive 0.9s6.0s26.3s5m 15.6s