assume that annual failure rate varies over the lifetime of disks in the previou

ID: 3535501 • Letter: A

Question

assume that annual failure rate varies over the lifetime of

disks in the previous talbe. Especiafically, assume that AFR is

three times as high in the first month of operation and doubles

every year starting the fifth year. How many disks would be

raplaced

after 7 years of operations? how about 10 years?

Please explain how you got you answers. for hte # of disk

replaced.

THank you

# of Drives : 1000

Hours/Drive: 8760

Hours/Failure: 1,000,000

The answer is 32.85 for 7 years and 237.25 for 10 years. I don't know why.

Failed Disks = No of Disks * Time Period / MTTF.

Given
No of Disk = # of Drives : 1000
Time Period = Hours/Drive: 8760
MTTF = Hours/Failure: 1,000,000

Failed Disks = No of Disks * Time Period / MTTF.= 1000*8760/1,000,000 = 9.

alternatively 9 out of 1000 means 0.9 % would fail per year.

thus.

after 7 years 7*0.9 = 6.3 % means 63 will fail thus 63 we have to replace.

after 10 years 10*0.9 = 9% means 90 will fail thus 90 we have to relace.

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