- Annualized failure rate
Annualized failure rate (AFR) is the relation between the mean time between failure (MTBF) and the assumed hours that a device is run per year, expressed in percent.
A disk drive's MTBF number may be 1,200,000 hours and the disk drive may be running 24 hours a day, seven days a week [Annualized Failure Rate (AFR) and Mean Time Between Failures (MTBF) in: [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] . One year has 8,760 hours.
then take the reciprocal of 136.9863 years
You can expect about 0.73 percent of the population of these disk drives to fail in the average year.
Another example: A disk drive's MTBF number may be 700,000 hours and the disk drive may be running 2400 hours a year [Annualized Failure Rate (AFR) and Mean Time Between Failures (MTBF) in: [http://www.seagate.com/staticfiles/support/disc/manuals/desktop/Barracuda%207200.10/100402371f.pdf Seagate Barracuda 7200.10 SATA Product Manual] , Page 42, Chapter 2.12: Reliability] .
then take the reciprocal of 291.6667 years
You can expect about 0.34 percent of the population of these disk drives to fail in the average year.
Now assuming you let the same disk run 24 hours a day, 7 days a week:
then take the reciprocal of 79.9087 years
You can expect about 1.25 percent of the population of these disk drives to fail in the average year.
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