Annualized Failure Rate
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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 Mean time between failures (MTBF) is the predicted elapsed time between inherent failures of a mechanical or electronic system during normal system operation. MTBF can be calculated as the arithmetic mean (average) time between failures of a syst ...
) 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 Population typically refers to the number of people in a single area, whether it be a city or town, region, country, continent, or the world. Governments typically quantify the size of the resident population within their jurisdiction using a ...
statistics that can not predict the behaviour of an individual unit.


Hard disk drives

For example, AFR is used to characterize the reliability of
hard disk drive A hard disk drive (HDD), hard disk, hard drive, or fixed disk is an electro-mechanical data storage device that stores and retrieves digital data using magnetic storage with one or more rigid rapidly rotating platters coated with magne ...
s. The relationship between AFR and MTBF (in hours) is: :AFR = 1-exp(-8766/MTBF) This equation assumes that the device or component is powered on for the full 8766 hours of a year, and gives the estimated fraction of an original sample of devices or components that will fail in one year, or, equivalently, 1 − AFR is the fraction of devices or components that will show no failures over a year. It is based on an exponential failure distribution (see failure rate for a full derivation). Note: Some manufacturers count a year as 8760 hours. This ratio can be approximated by, assuming a small AFR, :AFR = For example, a common specification for
PATA Pata or PATA may refer to: Places * Pata, Sulu, a Philippine municipality * Pata, Galanta District, a village in Slovakia * Pata, Central African Republic, a village * Pata village (Samoa), a village in Samoa * Pontrilas Army Training Area, a ...
and
SATA SATA (Serial AT Attachment) is a computer bus interface that connects host bus adapters to mass storage devices such as hard disk drives, optical drives, and solid-state drives. Serial ATA succeeded the earlier Parallel ATA (PATA) standard t ...
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. The AFR for a drive is derived from time-to-fail data from a reliability-demonstration test (RDT).. AFR will increase towards and beyond the end of the service life of a device or component. Google's 2007 study found, based on a large field sample of drives, that actual AFRs for individual drives ranged from 1.7% for first year drives to over 8.6% for three-year-old drives.. A CMU 2007 study showed an estimated 3% mean AFR over 1–5 years based on replacement logs for a large sample of drives..


See also

* Failure rate *
Frequency of exceedance The frequency of exceedance, sometimes called the annual rate of exceedance, is the frequency with which a random process exceeds some critical value. Typically, the critical value is far from the mean. It is usually defined in terms of the number ...


References

{{DEFAULTSORT:Annualized Failure Rate Engineering failures Rates