Drive Dilemma
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.