It is generally recognized that it is wise to back up computer data. Assume that

Question

It is generally recognized that it is wise to back up computer data. Assume that there is a 3% rate of disk drive failure in a year (based on data from various sources, including lifehacker.com) a. If you store all of your computer data on a single hard disk drive, what is the probability that the drive will fail during a year? If all of your computer data are stored on a hard disk drive with a copy stored one second hard disk drive, what is the probability that both drives will fail during a year? If all of your computer data are stored on a hard disk drive with a copy stored one second hard disk drive, what is the probability that you will not lose your data during a year? b. c.

Explanation / Answer

There is a 3% rate of disk drive failure in a year.

a. If all the computer data is stored on a single hard disk drive, probability that the drive will fail during a year = 3% = 0.03

b. Probability that both hard disk drive will fail = (Probability that single hard drive fails)2 = 0.032 = 0.0009 (i.e. 0.09%)

{Since disk drive failures are independent of each other}

c. If data is stored on a hard disk drive and a copy on single hard disk drive, then probability that you will not lose data during a year = 1 - Probability that both hard disk drive fails = 1 - 0.0009 = 0.9991 (i.e. 99.91%)

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