- 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.**Example**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: [*] . One year has 8,760 hours.*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:$frac\{1,200,000,hours\}\{8760\; ,\; hours\; /\; year\}=136.9863\; ,\; years$

then take the reciprocal of 136.9863 years

:$frac\{1\; ,\; failure\}\{136.9863\; ,\; years\}\; imes\; 100\%=0.73\%$

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:$frac\{700,000\; ,\; hours\}\{2400\; ,\; hours\; /\; year\}=291.6667\; ,\; years$

then take the reciprocal of 291.6667 years

:$frac\{1\; ,\; failure\}\{291.6667\; ,\; years\}\; imes\; 100\%=0.34\%$

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:

:$frac\{700,000\; ,\; hours\}\{8760\; hours\; /\; year\}=79.9087\; ,\; years$

then take the reciprocal of 79.9087 years

:$frac\{1\; ,\; failure\}\{79.9087\; ,\; years\}\; imes\; 100\%=1.25\%$

You can expect about 1.25 percent of the population of these disk drives to fail in the average year.

**ee also***

Failure rate **References**

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