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Availability % | Downtime per year | Downtime per month |
99.8% | 17.53 hours | 87.66 minutes |
99.9% ("three nines") | 8.77 hours | 43.83 minutes |
99.95% ("three and a half nines") | 4.38 hours | 21.92 minutes |
99.99% ("four nines") | 52.60 minutes | 4.38 minutes |
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Wikipedia