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 of a drive
or system failing. For example, an MTBF value of one million hours results in an AFR value of 0.876%. This means that of 114 drives, one fails on average every year. The AFR value and the value for the Mean Failure Interval (MFI) have the following relationship: AFR rate = 8760/MFI.