2009/7/18 Andy Smith <a...@strugglers.net>: > Hi James, > > On Sat, Jul 18, 2009 at 10:44:49PM +0100, James Courtier-Dutton wrote: >> Take an example of a SSD >> Manufacturer quotes: >> OCZ-120GB-Solid-State-Drive: MTBF 1.5 million hours. >> To me that means and MTBF of 171 years abouts. >> So, why do OCZ only guarantee it for 2 years? > > MTBF figures for hard drives (and possibly other things) are quoted > in terms of analysis of large numbers of that model. The item is > rated for 2 years of use. > > What they are saying is that if you got many of these items and ran > them simultaneously for 2 years then you should get 171 years > aggregate service out of them before any of them developed a fault. > > Or if you ran one item for 2 years then replaced it and kept going, > it should be 171 years before you had a failure inside the 2 years > of any individual item. > > Cheers, > Andy >
To get a MTBF figure: Approx MTBF = ( Number of Devices tested * Test time ) / Number of failures. So, you are right, there is no indication as to what might happen after 2 years. The model for failures is a U curve anyway. In that some failures happen early on due to burn in etc., then it is fairly quite for a bit, and then the failures start happening again at an exponential rate. This link helped me http://www.vicr.com/documents/quality/Rel_MTBF.pdf -- Please post to: Hampshire@mailman.lug.org.uk Web Interface: https://mailman.lug.org.uk/mailman/listinfo/hampshire LUG URL: http://www.hantslug.org.uk --------------------------------------------------------------