Annualized failure rate
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]
[edit] Hard drives
A vendor-quoted MTBF implies that half the drives in a large population will fail within that time of operation.[2] 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 1.46% 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]
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.[4]
[edit] See also
[edit] References
- ^ Annualized Failure Rate (AFR) and Mean Time Between Failures (MTBF) in: Seagate Barracuda ES SATA Product Manual, Page 29, Chapter 2.12: Reliability
- ^ a b Robin Harris. Google’s Disk Failure Experience.
- ^ a b Gerry Cole. Estimating Drive Reliability in Desktop Computers and Consumer Electronics Systems
- ^ AFR broken down by age groups: Failure Trends in Large Disk Drive Population. page 4, figure 2 and subsequent figures.
