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High availability (HA) is a characteristic of a system that aims to ensure an agreed level of operational performance, usually uptime, for a higher than normal period. [ 1 ] There is now more dependence on these systems as a result of modernization.
Availability includes non-operational periods associated with reliability, maintenance, and logistics. This is measured in terms of nines. 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.
In reliability engineering, the term availability has the following meanings: . The degree to which a system, subsystem or equipment is in a specified operable and committable state at the start of a mission, when the mission is called for at an unknown, i.e. a random, time.
The terms high availability, continuous operation, and continuous availability are generally used to express how available a system is. [3] [4] The following is a definition of each of these terms. High availability refers to the ability to avoid unplanned outages by eliminating single points of failure. This is a measure of the reliability of ...
Five nines, commonly taken to mean "99.999%", may refer to: High availability of services, when a service is available for 99.999% of the time, or around 5 minutes of downtime per year; Nine (purity), a 99.999% pure substance; German 15 cm (5.9 in) artillery shells used in World War I
1 troy ounce of four nines fine gold (999.9) Nines are an informal logarithmic notation for proportions very near to one or, equivalently, percentages very near 100%. Put simply, "nines" are the number of consecutive nines in a percentage such as 99% (two nines) [1] or a decimal fraction such as 0.999 (three nines).
Website monitoring can be done from both inside and outside of a corporate firewall.Traditional network management solutions focus on inside the firewall monitoring, whereas external performance monitoring will test and monitor performance issues across the Internet backbone and in some cases all the way to the end-user.
High-test peroxide (HTP) is a highly concentrated (85 to 98%) solution of hydrogen peroxide, with the remainder consisting predominantly of water.In contact with a catalyst, it decomposes into a high-temperature mixture of steam and oxygen, with no remaining liquid water.