Slashdot Mirror
Calculating the Mean Time Between Failures?
Blue Booger asks: "I was looking over some fibrechannel hard drives and noticed that the Mean Time Between Failures was rated at 1.2 million hours. I thought that was pretty high, and figured it up to be close to 137 YEARS!! I went to check some regular IDE drives just for comparison, and they were rated at 500,000 hours (57 years). Now, as I understand it, this is supposed to be the average time that you can expect the drive to last before failures. I rarely have an IDE drive last more than 4 years, and my record is 10 years, so what is the deal? BTW, that is 57 years running 24 hours a day...the MTBF is rated as power on time. Here you can find Western Digital's glossary that defines the term MTBF (pdf). Here you can find a spec sheet on one of their 20GB IDE drives. I checked, and Seagate also lists similar MTBFs. How the heck are they coming up with these numbers?"
Cisco used to sell Catalyst 3548XL switches that were listed as having a MTBF of 120,000+ hours. Their current replacement for that line (3550)comes in at 163,000+ hours. We had 7 of 24 3548XL switches fail in the first year we had them. They had poor air flow from a tiny fan, no heatsinks and tons of hot chips. The newer model has the same issue, though they did stuff a cheap foam baffle in the case to get air to flow closer to the chips, none of which have heatsinks. I have no idea how they tested them and got a MTBF of 13 years.