In partial answer to the subject question, let us apply the mode of analysis used by the drive manufacturers to human life expectancy, as if Humans were one of their products. That is, what is the Human AFR and MTBF? Unlike for disk drives, we can easily obtain a table of USA mortality rates, this one is for the year 2007:
http://www.cdc.gov/nchs/data/dvs/MortFinal2007_Worktable23r.pdf Looking at the first row of the table, which is the data for the whole country, we see that it has a bathtub shaped curve, with a relatively high "early failure rate", which decreases to a minimum for the ages 5-14, and then an increasing "failure rate" with advancing years. Now assume the "manufacturer" calculates the AFR assuming a "working life" for the "product" of 20 years. The total "failures"/100,000 over that period measured in 2007 were: 685.4 + 4*28.6 + 10*15.3 + 5*79.9 = 1352.3 Giving a 20 year failure rate of 1352.3 / 100000 = .013523 and an AFR of .013523/20 = .000676, or .0676%. So the MTBF for the humans (in years, not hours), is 1/.000676 = 1479 years. This number is just as nonsensical for people as 150 years is for disks. In the human case, since we have all the data, we can see exactly why the result is so far off. In rough terms the human mortality rate doubles for every decade of age. Consequently any AFR calculated up to an age below the actual MTBF (average lifespan) will be an underestimate, and the earlier the cut off, the further off the value will be. This is on top of the other issue which affects the calculations for disks - the definition of a "failed unit" used by the manufacturers is much less stringent than that employed by the end users/vendors. Regards, David Mathog [email protected] Manager, Sequence Analysis Facility, Biology Division, Caltech _______________________________________________ Beowulf mailing list, [email protected] sponsored by Penguin Computing To change your subscription (digest mode or unsubscribe) visit http://www.beowulf.org/mailman/listinfo/beowulf
