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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 Every request received by a non-failing node in the system must result in a response. This is the definition of availability in CAP theorem as defined by Gilbert and Lynch. [1] Note that availability as defined in CAP theorem is different from high availability in software architecture. [5] Partition tolerance
Human error, human performance, and human reliability are especially important to consider when work is performed in a complex and high-risk environment. [ 2 ] Strategies for dealing with performance-shaping factors such as psychological stress , cognitive load , fatigue include heuristics and biases such as confirmation bias , availability ...
Reliability: Ability to perform a specific function and may be given as design reliability or operational reliability Availability : Ability to keep a functioning state in the given environment Maintainability : Ability to be timely and easily maintained (including servicing, inspection and check, repair and/or modification)
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 ...
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 number of standby servers is a tradeoff between cost and reliability requirements. N-to-1 — Allows the failover standby node to become the active one temporarily, until the original node can be restored or brought back online, at which point the services or instances must be failed-back to it in order to restore high availability.
High availability is a high percentage of time that the system is functioning. It can be formally defined as (1 – (down time/ total time))*100%. Although the minimum required availability varies by task, systems typically attempt to achieve 99.999% (5-nines) availability.