High Availability Lens 2

In our last post HA Lens 1, we have seen what is mean by High Availability. Availability can be measured in numbers provided these numbers are used consistently for behavior of given system. Availability is essentially a function of Reliability and it is just one of the factors that affects system availability. When we refer to high available system, we are referring to whole system that we are trying to highly available.
Availability can be expressed in % time in hours per week,month or year and measured using following formula,

                     (Operating Time) 
Availability = ------------------------------
               (Operating Time + Downtime)

Another common formula to measure availability is,
Availability = ------------------------------
                     (MTBF + MTTR) 
MTBF = Mean Time Between Failure
MTTR = Mean Time To Repair

By Mandar Pise

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