Annualized failure rate: Difference between revisions
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{{Short description|Probability that a device or component will fail during a year of use}} |
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'''Annualized failure rate''' ('''AFR''') is the relation between the mean time between failure ([[Failure rate|MTBF]]) and the hours that a number of devices are run per year, expressed in percent. AFR does not specifically apply to a single component, but rather to a population of like components. AFR and MTBF as given by vendors may be [[Statistical population|population]] statistics that are not relevant to individual units.<ref>Annualized Failure Rate (AFR) and Mean Time Between Failures (MTBF) in: |
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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 ([[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="Seagate">{{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 }}</ref> |
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[http://www.seagate.com/staticfiles/support/disc/manuals/enterprise/Barracuda%20ES/SATA/100424667b.pdf Seagate Barracuda ES SATA Product Manual], Page 29, Chapter 2.12: Reliability</ref> |
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==Hard drives== |
==Hard disk drives== |
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For example, AFR is used to characterize the reliability of [[hard disk drive]]s. |
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A vendor-quoted [[Mean time between failures|MTBF]] implies that half the drives in a large population will fail within that time of operation.<ref name=harris>Robin Harris. [http://storagemojo.com/2007/02/19/googles-disk-failure-experience/ Google’s Disk Failure Experience].</ref> For example, a common specification for [[Parallel ATA|PATA]] and [[SATA]] drives may be 300,000 MTBF, implying that in a 600,000 drive sample, one drive failure may occur per hour if failures were evenly distributed, translating to 8760 drive failures per year or a theoretical 1.46% annualized failure rate.<ref name=harris/> |
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The relationship between AFR and MTBF (in hours) is:<ref name="Seagate" /> |
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[[Seagate Technology|Seagate]] estimates the MTBF for a drive as the number of power-on hours per year divided by the first year AFR.<ref name=cole>Gerry Cole. [http://www.cs.virginia.edu/~jck/cs686/papers/cole.pdf Estimating Drive Reliability in Desktop Computers and Consumer Electronics Systems]</ref> The AFR for a drive is derived from time-to-fail data from a reliability-demonstration test (RDT).<ref name=cole/> |
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:<math>AFR = 1-exp(-8766/MTBF)</math> |
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This equation assumes that the device or component is [[Power-on hours|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#Failure rate in the continuous sense|failure rate]] for a full derivation). |
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Google's 2007 study found that actual AFRs for individual drives ranged from 1.7% for first year drives to over 8.6% for three-year old drives.<ref>AFR broken down by age groups: [http://labs.google.com/papers/disk_failures.pdf Failure Trends in Large Disk Drive Population]. page 4, figure 2 and subsequent figures.</ref> |
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Note: Some manufacturers count a year as 8760 hours.<ref>{{Citation | url = http://knowledge.seagate.com/articles/en_US/FAQ/174791en?language=en_US | title = Hard disk drive reliability and MTBF / AFR}}</ref> |
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This ratio can be approximated by, assuming a small AFR, |
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:<math>AFR = {8766 \over MTBF} </math> |
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For example, a common specification for [[Parallel ATA|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. |
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The AFR for a drive is derived from time-to-fail data from a reliability-demonstration test (RDT).<ref name = cole>{{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}}.</ref> |
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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.<ref>{{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}}.</ref> A CMU 2007 study showed an estimated 3% mean AFR over 1–5 years based on replacement logs for a large sample of drives.<ref name = schroeder>{{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}}.</ref> |
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==See also== |
==See also== |
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* [[Failure rate]] |
* [[Failure rate]] |
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* [[Frequency of exceedance]] |
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== References == |
== References == |
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{{Reflist}} |
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<references /> |
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{{DEFAULTSORT:Annualized Failure Rate}} |
{{DEFAULTSORT:Annualized Failure Rate}} |
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[[Category: |
[[Category:Engineering failures]] |
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[[Category:Rates]] |
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Latest revision as of 23:49, 8 March 2024
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 disk drives[edit]
For example, AFR is used to characterize the reliability of hard disk drives.
The relationship between AFR and MTBF (in hours) is:[1]
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.[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.
The AFR for a drive is derived from time-to-fail data from a reliability-demonstration test (RDT).[3]
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.[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.[5]
See also[edit]
References[edit]
- ^ a b "Diving into "MTBF" and "AFR": Storage Reliability Specs Explained". Inside IT Storage. Seagate. Apr 2010. Archived from the original on 2010-05-01.
{{cite web}}: CS1 maint: bot: original URL status unknown (link) - ^ Hard disk drive reliability and MTBF / AFR
- ^ 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), 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?.