Reliability Vs Availability
Reliability= e ( -t / MTBF)
Availability = Uptime/Total Time
= MTBF/ (MTBF + MTTR)
A system can be highly reliable but have low availability if it takes a long time to repair when it does fail.
A system may have moderate reliability but high availability if repairs are quick and efficient.
Availability= ƒ( Reliability, Maintainability)
Reliability 95% :
There is a 95% probability that the pump will not fail during a year.
There is a 5% probability that the pump will fail in a year.
If the Pump is operated for 20 years, then it may fail once( 20*0.05=1)
Availability:
Pump is available for 95% of time in year. Means the Pump is available for =365*0.95= 346.75 Days
Rest of the time( 365-347= 18 days), it is not be available.