Reliability: nines

The uptime and reliability of a system is measured in "nines". "Five nines" means 99.999% availability, which means downtime of approximately five minutes and fifteen seconds per year.

see the below table

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                  per year      per month      per week
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98%               7.30 days     14.4 hours     3.36 hours
99%               3.65 days     7.3 hours      1.68 hours
99.5%             1.83 days     3.6 hours      50.4 min
99.9%             8.76 hours    43.2 min       10.1 min
99.99%            52.6 min      4.32 min       1.01 min
99.999%           5.26 min      25.9 sec       6.05 sec
99.9999%          31.5 sec      2.59 sec       0.605 sec
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