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by esrauch
5350 days ago
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The number of nines refers to how reliable something is. "Four nines" means that it is up 99.99% of the time, or 0.01% of downtime, which is 0.0001 * 365 * 24 = just shy of 1 hour of downtime per year (or 1 day downtime every 30 years). These things are usually specified in SLA (service level agreements) where if the provider exceeds the amount of downtime in the SLA means that you don't have to pay. If Amazon has a 4-nines SLA that means that you don't get any discount if they have 1 hour down per year. |
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