I was trying to solve the following question in software architecture.
A software system crashed 20 times in an year and for each crash, it takes 2 minutes to restart. Calculate availability in that year
I used the formula MTBF/(MTBF+MTTR) as given MTTR =2 minutes. But how can I calculate MTBF and availability?
- MTBF = Mean Time Between Failures
- MTTR = Mean Time To Repair
Update : I did it like
MTBF = 365*24*60-40/ 20, MTTR = 2*20
Best Answer
You would normally assume a system has 24/7 (i.e. 'round the clock) availability. Therefore, in minutes, it needs to be available for 365 (days) * 24 (hours) * 60 (minutes) =
525600
minutes.Your MTBF then becomes fairly simple, it's just that amount of time divided by the number of failures (20). Therefore: MTBF =
525600 / 20 =
26280
(minutes MTBF).Then applying MTBF/(MTBF+MTTR) gives: 26280 (MTBF) / (26280+2) = 0.99992390229054105471425310098166 - or approx. 99.99% availability.
Hope that makes sense!