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Another memory trick to calculate the allowed downtime duration for an "-nines" availability percentage is to use the formula seconds per day. For example, 90% ("one nine") yields the exponent 4 − 1 = 3 {\displaystyle 4-1=3} , and therefore the allowed downtime is 8.64 × 10 3 {\displaystyle 8.64\times 10^{3}} seconds per day.
In this context, a "one nine" (90%) uptime indicates a system that is available 90% of the time or, as is more commonly described, unavailable 10% of the time – about 72 hours per month. [8] A "five nines" (99.999%) uptime describes a system that is unavailable for at most 26 seconds per month. [8]
Uptime is a measure of system reliability, expressed as the period of time a machine, typically a computer, has been continuously working and available. Uptime is the opposite of downtime . Htop adds an exclamation mark when uptime is longer than 100 days.
Diagram showing the cumulative distribution function for the normal distribution with mean (μ) 0 and variance (σ 2) 1. These numerical values "68%, 95%, 99.7%" come from the cumulative distribution function of the normal distribution.
Continuous availability is an approach to computer system and application design that protects users against downtime, whatever the cause and ensures that users remain connected to their documents, data files and business applications.
In an increasing system, the time constant is the time for the system's step response to reach 1 − 1 / e ≈ 63.2% of its final (asymptotic) value (say from a step increase). In radioactive decay the time constant is related to the decay constant ( λ ), and it represents both the mean lifetime of a decaying system (such as an atom) before it ...
A tolerance interval (TI) is a statistical interval within which, with some confidence level, a specified sampled proportion of a population falls. "More specifically, a 100×p%/100×(1−α) tolerance interval provides limits within which at least a certain proportion (p) of the population falls with a given level of confidence (1−α)."
Each row of points is a sample from the same normal distribution. The colored lines are 50% confidence intervals for the mean, μ.At the center of each interval is the sample mean, marked with a diamond.