Annualized failure rate: Difference between revisions
→Hard drives: +2. |
Punctuation cleanup |
||
Line 1: | Line 1: | ||
'''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 ([[Failure rate|MTBF]]) and the hours that a number of devices are run per year. AFR is estimated from a sample of like components |
'''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 ([[Failure rate|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 [[Statistical population|population]] statistics that can not predict the behaviour of an individual unit.<ref name="Segate">{{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}}</ref> |
||
==Hard drives== |
==Hard drives== |
Revision as of 06:44, 1 February 2014
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.[1]
Hard drives
For example, AFR is used to characterize the reliability of hard disk drives.
The relationship between AFR and MTBF is:[1]
This equation assumes that the drives are powered on for the full 8760 hours of a year, and gives the estimated fraction of an original sample of drives that will suffer from disk failures, or, equivalently, 1 − AFR is the fraction of drives that will show no failures over a year. It is based on an exponential failure distribution (see Failure rate for a full derivation).
This can be approximated by, assuming a small AFR,
- (expressed in %).
For example, a common specification for PATA and SATA drives may be 300,000 MTBF, giving a theoretical 2.88% annualized failure rate i.e. a 2.88% 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).[2]
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.[3] A CMU 2007 study showed an estimated 3% mean AFR over 1–5 years based on replacement logs for a large sample of drives.[4]
See also
References
- ^ a b "Diving into "MTBF" and "AFR": Storage Reliability Specs Explained". Inside IT Storage. Seagate. Apr 2010.
- ^ Cole, Gerry, Estimating Drive Reliability in Desktop Computers and Consumer Electronics Systems (PDF), Virginia.
- ^ "AFR broken down by age groups", Failure Trends in Large Disk Drive Population (PDF), Google, p. 4, figure 2ff.
- ^ Schroeder, Bianca; Gibson, Garth A, Disk Failures in the Real World: What Does an MTTF of 1,000,000 Hours Mean to You?.