annual failure rate (MTBF) (AFR)

The Annual Failure Rate(AFR) is an intuitive measure of the operational reliability of systems and components, comparable to the Mean Time Between Failures ( MTBF).

Since data for mean time between failures can be in the tenths of a part per thousand, the annual failure rate is used to indicate the probability that a drive or system will fail. For example, an MTBF value of one million hours results in an AFR value of 0.876%. This means that out of 114 drives, one fails on average every year.

The AFR value and the Mean Failure Interval (MFI) value are related as follows: AFR rate = 8760/MFI.