annualized failure rate
{{Short description|Probability that a device or component will fail during a year of use}}
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.{{cite web|url=http://enterprise.media.seagate.com/2010/04/inside-it-storage/diving-into-mtbf-and-afr-storage-reliability-specs-explained/ |title=Diving into "MTBF" and "AFR": Storage Reliability Specs Explained |work=Inside IT Storage |publisher=Seagate |date=Apr 2010 |url-status=bot: unknown |archiveurl=https://web.archive.org/web/20100501151901/http://enterprise.media.seagate.com/2010/04/inside-it-storage/diving-into-mtbf-and-afr-storage-reliability-specs-explained/ |archivedate=2010-05-01 }}
Hard disk drives
For example, AFR is used to characterize the reliability of hard disk drives.
The relationship between AFR and MTBF (in hours) is:
:
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.{{Citation | url = http://knowledge.seagate.com/articles/en_US/FAQ/174791en?language=en_US | title = Hard disk drive reliability and MTBF / AFR}}
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.
The AFR for a drive is derived from time-to-fail data from a reliability-demonstration test (RDT).{{Citation | first = Gerry | last = Cole | url = http://kc.ors-pc.com/bbs/img/8.pdf | title = Estimating Drive Reliability in Desktop Computers and Consumer Electronics Systems | publisher = Virginia}}.
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.{{Citation | contribution = AFR broken down by age groups | url = http://research.google.com/archive/disk_failures.pdf | title = Failure Trends in Large Disk Drive Population | at = p. 4, figure 2ff}}. A CMU 2007 study showed an estimated 3% mean AFR over 1–5 years based on replacement logs for a large sample of drives.{{Citation | url = http://www.usenix.org/events/fast07/tech/schroeder.html | title = Disk Failures in the Real World: What Does an MTTF of 1,000,000 Hours Mean to You? | first1 = Bianca | last1 = Schroeder|author1-link= Bianca Schroeder | first2 = Garth A | last2 = Gibson | author2-link = Garth A. Gibson}}.