Annualized failure rate (AFR) gives the estimated probability that a device or component will fail during a full year of use.
It is a relation between the mean time between failure (MTBF) and the hours that a number of devices are run per year.
AFR is estimated from a sample of like components—AFR and MTBF as given by vendors are population statistics that can not predict the behaviour of an individual unit.
[2] This ratio can be approximated by, assuming a small AFR, For example, a common specification for PATA and SATA drives may be an MTBF of 300,000 hours, giving an approximate theoretical 2.92% annualized failure rate i.e. a 2.92% chance that a given drive will fail during a year of use.
[4] A CMU 2007 study showed an estimated 3% mean AFR over 1–5 years based on replacement logs for a large sample of drives.