Drive Dilemma

Mac Format - - APPLE TALK -

On page 36 – the ul­ti­mate so­lu­tion – of is­sue 288 there is ref­er­ence to “Mean Time Be­fore Fail­ure” which is some­thing I’d not heard of be­fore and did not know how to cal­cu­late. I use a set of Western Dig­i­tal My Pass­port 1TB drives to back up to Time Ma­chine. I went to the WD site to find what the MTBF was for these drives to find that it said they no longer pro­vide this in­for­ma­tion. In­stead it said: “We no longer mea­sure the re­li­a­bil­ity of our hard drives us­ing Mean Time Be­tween Fail­ure (MTBF). Our cur­rent drive re­li­a­bil­ity is mea­sured us­ing Com­po­nent De­sign Life (CDL) and An­nu­al­ized Fail­ure Rate (AFR). The Com­po­nent De­sign Life of the drive is five years and the An­nu­al­ized Fail­ure Rate is less than 0.8%”.

Would you please trans­late this for a non-tech­ni­cal per­son. What does the 0.8% re­fer to; is it a per­cent­age of drives sold each year? Pre­sum­ably Com­po­nent De­sign Life means that the drives are de­signed to last five years. So for a good safety fac­tor is it best to change them af­ter three years? I know I could ask WD about this but I’m sure that there are many of your read­ers in a sim­i­lar po­si­tion to my­self who would welcome fur­ther ad­vice. John Myring Chris­tian Hall says: MTBF is ac­tu­ally an en­gi­neer­ing stan­dard that’s ex­pressed as a com­plex math­e­mat­i­cal for­mula. It, and other sim­i­lar meth­ods, are cal­cu­lated by con­stantly run­ning sam­ples of the drive for a short amount of time, analysing the re­sul­tant wear and tear upon the phys­i­cal com­po­nents, and ex­trap­o­lat­ing to pro­vide a rea­son­able es­ti­mate of its life­span. It’s a ‘mil­i­tary stan­dard’ but deemed as not the best method to cal­cu­late fail­ure rates by most drive man­fac­tur­ers now. AFR is broad­lly speak­ing the in­dus­try re­place­ment and the per­cent­age you cite refers to the prob­a­ble per­cent­age of fail­ures per year based on the man­u­fac­turer’s to­tal ‘in­stalled’ units – namely, those sold. So, just un­der a one in 100 chance of a drive fail­ure in its ‘De­sign Life’. That’s not bad at all, and you shouldn’t feel pres­sured to change ev­ery three or four years. As ever, back­ups are your top pri­or­ity, what­ever drive you’re us­ing.

In­cor­rect CD de­tails likely stem from mul­ti­ple matches in a data­base.

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