Availability is the need to ensure that the business purpose of the system can be met and that it is accessible to those who need to use it.
Availability (Wikipedia)
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 probability that an item will operate satisfactorily at a given point in time when used under stated conditions in an ideal support environment.
Normally high availability systems might be specified as 99.98%, 99.999% or 99.9996%.
