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In general, the number of nines is not often used by a network engineer when modeling and measuring availability because it is hard to apply in formula. More often, the unavailability expressed as a probability (like 0.00001), or a downtime per year is quoted. Availability specified as a number of nines is often seen in marketing documents.
Five-9's (99.999%) means less than 5 minutes when the system is not operating correctly over the span of one year. Availability is only meaningful for supportable systems. As an example, availability of 99.9% means nothing after the only known source stops manufacturing a critical replacement part.
Every 1.38 million years (twice in history of humankind) μ ± 6.5σ: 0.999 999 999 919 680: 8.032 × 10 −11 = 0.080 32 ppb = 80.32 ppt: 1 in 12 450 197 393: Every 34 million years (twice since the extinction of dinosaurs) μ ± 7σ: 0.999 999 999 997 440: 2.560 × 10 −12 = 2.560 ppt: 1 in 390 682 215 445: Every 1.07 billion years (four ...
The purity of a gas is generally expressed as a grade prefixed with the letter N (rather than postfixed), indicating the "number of nines" in the percentage or decimal fraction. For example, a N2.0 gas is 99% (two nines) pure and 1% impurities by volume; a N6.0 gas is 99.9999% (six nines) pure, with 1 part per million (1 ppm or 1 vpm, volume ...
Microsoft Azure uses large-scale virtualization at Microsoft data centers worldwide and offers more than 600 services. [11] Microsoft Azure offers a service level agreement (SLA) that guarantees 99.9% availability for applications and data hosted on its platform, subject to specific terms and conditions outlined in the SLA documentation.
A Cisco router had been reported to have been running continuously for 21 years as of 2018. [6] As of April 11, 2023, the uptime had increased to 26 years, 25 weeks, 1 day, 1 hour, and 8 minutes until the router was later decommissioned and the final report of the uptime was 26 years, 28 weeks, 2 days, and 6 minutes. [7] [8]
[citation needed] A hosting provider's Service Level Agreement (SLA) may include a certain amount of scheduled downtime per year in order to perform maintenance on the systems. This scheduled downtime is often excluded from the SLA timeframe, and needs to be subtracted from the Total Time when availability is calculated.
The number , whose typical value is close to but not greater than 1, is sometimes given in the form (or as a percentage % ()), where is a small positive number, often 0.05. By definition, the bounds () and () are to be constructed in such a way that as long as is collected randomly, i.e. the model assumption about its probability distribution ...