On 28 March 2016 at 00:32, Attila Kinali <[email protected]> wrote: > > Yes, the MTBF is a very simplicistic measure and there are a couple > of assumptions in its calculation which do not hold generally (or > rather, it's rather seldom that they hold).
It get's "interesting" when you look at the MTBF times on hard disks. Some of the figures quoted in hours related to an MTBF of over 100 years. From what I read before, this was based on you replacing the drive at the end of its service life (typically 3 years for consumer drives and 5 years for enterprise grade disks). So no individual drive was ever expected to last 100 years, but if you kept replacing the drives ever 3~5 years, the average time of an unexpected failure would be 100 years. I guess its a bit like a car - the engine might run for 250,000 miles, but if you never change the oil or the camshaft belt, it is not going to last. I note Seagate have dropped the use of MTBF: http://knowledge.seagate.com/articles/en_US/FAQ/174791en?language=en_US changing to an Annualized Failure Rate (AFR). I don't think Seagate will ever get a real measure of this, as in many cases people are just going to throw a hard disk in the bin if it fails, even if under warranty. In many cases the warranty is with an OEM, so even if you buy a new drive sold originally to Dell, you can't return it unless you are Dell. Also with hard drive capacities growing quite fast, if a drive does fail you will probably chose to replace it with one of higher capacity. Dr. David Kirkby Ph.D CEng MIET Kirkby Microwave Ltd Registered office: Stokes Hall Lodge, Burnham Rd, Althorne, Essex, CM3 6DT, UK. Registered in England and Wales, company number 08914892. http://www.kirkbymicrowave.co.uk/ Tel: 07910 441670 / +44 7910 441670 (0900 to 2100 GMT only please) _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
