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


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!

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.