Talk:Mean time between failures
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Put your text for the new page here. The MTBF metric has virtually no value when being used to predict failure rate. Here, we are addressing the so called random failure. This fact has been demonstrated many times during the last 40 years. The planning /R & D phaphase of Large weapon systems were plagued with this nonsense. After 5 - 10 years actual failure data was shown to have no (NONE) correlation with the earler predictions. Effort related to predicting failure rate should be eliminated from all R & D effort dmiller897@aol.com
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[edit] Merge Alert
Another article on the same subject is at Mean time between failures. That text needs to be merged with this article (Mean time between failure is probably the best title; See Wikipedia:naming conventions). --mav
- I know we have the convention of naming articles in non-plural fashion, but how can you have a mean time between a single failure? -- Wapcaplet 19:12 3 Jun 2003 (UTC)
- Besides, "mean time between failures" is singular already; "mean times between failures" would be plural. -- John Owens 19:17 3 Jun 2003 (UTC)
I have moved this to Mean time between failures, per the discussion above. -- Wapcaplet 22:44 3 Jun 2003 (UTC)
[edit] What units?
I'm assuming this should be days, but could someone specify what this is measured in? Thanks.
[edit] Real-world example
I have no idea how to use the information in the article. For example, Seagate's largest HDD available is quoted as having a MTBF of 1,200,000. Obviously they don't mean it will last 1.2 million hours, because that is more than 136 years. It would help if someone could write an explanation of how I could work out how long I could expect a HDD to last, given a MTBF of 1.2m hours. Thanks Cagliost 21:03, 21 January 2007 (UTC)
The 1.2 million hours stated is only of limited use to people who are deploying or keeping track of many thousands of units in actual operation. The calculated MTBF is first done by putting all of the individual reliability information for all of the parts into a computer that uses the Belcore method for summing all of the values together into a "composite" figure. In the case of the disk drive, the motors, bearings, voice coils ASICS etc. all have values that are calculated together. Power components such as discrete power components will bring this composite figure down. So, the calculated MTBF for the HDD is most likely 1.2 million hours. Then the field population is tracked by how many confirmed failures are counted. I think many of these for disk drives are not counted because they are not returned to repair centers, more likely thrown away if they fail.
The operating hours of the total field population is added up and then divided by the Failures in Time or FIT which gives an "actual" MTBF figure. So it is this number that tells you the actual frequency of failure, in hours of run time across the field population. It is really meaningless to an individual user of a hard drive. The bottom line is that with a calculated MTBF of 1.2 million hours you should never see a functional failure of your hard drive unless it is being abused, overheated etc. In addition hard drives are rated differently depending on whether they are OEM (enterprise)models or consumer models. Enterprise models cost more and are rated at 100% duty cycle, where consumer models are rated at a much lower duty cycle.
ReliableEngineer 21:12, 22 January 2007 (UTC)
Thanks! So basically MTBF tells me, a home user, nothing about how long a HDD will last. I've been getting 5-8 years in desktops. But now I'm running a server, and I've heard claims that it's better to run an HDD constantly, because it is the spin-up and spin-down that wears the disks out. I've been unable to verify this, so have no idea if it's true or not! cagliost 15:14, 12 February 2007 (UTC)
- Well, MTBF tells you something about how many failures you can expect within the devices's rated lifetime, but as used by HDD manufacturers, it doesn't tell you much about the rated lifetime. (You can argue that this is somewhat disingenuous on their part, and I don't think I'll disagree with you.) "Five years" is a typical rated lifetime, by the way.
- Meanwhile, yes, spin-ups and spin-downs are bad for the life of the drive as they cause head touchdowns, and any given disk drive is only rated for a certain number of touchdowns (or its wearout life is stated in terms of, say "8 hour cycles with one take-off and on-landing" bracketing each cycle). But then again, while the disk is stopped, the spindle bearings aren't wearing out. So it's a tradeoff.Generally speaking, server disk drives tend to like long spin cycles with fewer touchdowns while laptop disk drives are rated for many more touchdowns so the drive can be spun-down to conserve power.
- Atlant 15:21, 12 February 2007 (UTC)
[edit] Fix the Freakin' Title!
For some reason, Mean time between failures now redirects here. Someone needs to fix this. As was pointed out above, the one and only proper title for this article is Mean time between failures, with a final s. Rocinante9x 22:03, 28 January 2007 (UTC)
[edit] Related: Software Safety
I deleted the short paragraph alluding to software in systems, since it was very crappily written and linked to a non-existent article. Rocinante9x 20:45, 6 February 2007 (UTC)
[edit] Merge suggestion
I believe that there is so much overlap between this MTBF article and Failure rate that it might be best to merge the two articles. Failure rate seems to be the more general topic, so I would suggest merging with Failure rate and redirecting MTBF. However, I would want to make sure all the points in the MTBF article are carried over to Failure rate, such as the section on Problems with MTBF. Any comments on this suggestion would be appreciated. Wyatts 21:25, July 21, 2005
