Annualized failure rate: Difference between revisions
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==Hard drives== |
==Hard drives== |
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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 2.88% annualized failure rate.<ref name=harris/> |
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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/> |
[[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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Revision as of 23:31, 1 December 2012
Annualized failure rate (AFR) is the relation between the mean time between failure (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 population statistics that are not relevant to individual units.[1]
Hard drives
For example, a common specification for 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 2.88% annualized failure rate.[2]
Seagate estimates the MTBF for a drive as the number of power-on hours per year divided by the first year AFR.[3] The AFR for a drive is derived from time-to-fail data from a reliability-demonstration test (RDT).[3]
The relationship between AFR and MTBF is: [4]
(note that this equation assumes that the drives are powered on for the full 8760 hours of a year, and gives the fraction of the original sample of drives that will show 1 or more disk failures, or, equivalently, 1 - AFR is the fraction of drives that will show no failures over a year)
or approximately, [5]
- (expressed in %)
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.[6]
See also
References
- ^ Annualized Failure Rate (AFR) and Mean Time Between Failures (MTBF) in: Seagate Barracuda ES SATA Product Manual, Page 29, Chapter 2.12: Reliability
- ^ Cite error: The named reference
harriswas invoked but never defined (see the help page). - ^ a b Gerry Cole. Estimating Drive Reliability in Desktop Computers and Consumer Electronics Systems
- ^ ""Diving into "MTBF" and "AFR": Storage Reliability Specs Explained". Inside IT Storage. Segate Enterprise".
- ^ http://forums.whirlpool.net.au/archive/920864
- ^ AFR broken down by age groups: Failure Trends in Large Disk Drive Population. page 4, figure 2 and subsequent figures.