OK, so you know how many (most?) computer components' failure rates follow the "bathtub curve":
http://users.ece.cmu.edu/~koopman/des_s99/sw_reliability/Image1.gif
They either die quickly due to egregious manufacturing faults, or live a long time (near 0% failure rate), and then all start dying as they get really old.
The bathtub curve occurs in tons of places, like with a simple light bulb.
As per my experience (probably dealing with over 1000 drives personally), and google's studies, as well as anecdotal information, hard drives are different. The failure rate seems to be bathtub-ish. The initial failure rate is fairly bathtub. But the useful-life period is at a much higher level and seems to grow slightly, meaning instead of dropping to near-zero failures during useful life, they drop to around 15% failure rate each year, mostly independent of age. Then, in the old-age phase they seem to ramp up much slower towards death. It's not a hockey-stick right edge, it's more a constant gentle hill slope. We all have seen many drives that are still running after 8, 10, 20 years. In fact, it seems more of a survival of the fittest system (maybe like turtles?), where once they live to a certain age, many go on to live far beyond the average.
Anyhow, my question is, what else in the non-computer world has a failure graph like hard drives? Something easy for a neophyte to grasp. Normal bathtubs have lightbulbs. What analogy can be used for hard drives? I haven't been able to think of any!
Surely there must be one??
The obvious analogy that for obvious reasons* won't have occurred to you: cars. If you don't get a lemon, it's probably good for a while, but eventually starts to break down. Also, historically, humans - at least in ages and places where infant mortality is/was a significant drag on population growth.
-Adam
*for those of you who don't know Trevor well, his 25(?)-year-old car is lovingly & painstakingly maintained in near-new condition.
On September 3, 2014 2:10:53 PM CDT, Trevor Cordes trevor@tecnopolis.ca wrote:
OK, so you know how many (most?) computer components' failure rates follow the "bathtub curve":
http://users.ece.cmu.edu/~koopman/des_s99/sw_reliability/Image1.gif
They either die quickly due to egregious manufacturing faults, or live a long time (near 0% failure rate), and then all start dying as they get really old.
The bathtub curve occurs in tons of places, like with a simple light bulb.
As per my experience (probably dealing with over 1000 drives personally), and google's studies, as well as anecdotal information, hard drives are different. The failure rate seems to be bathtub-ish. The initial failure rate is fairly bathtub. But the useful-life period is at a much higher level and seems to grow slightly, meaning instead of dropping to near-zero failures during useful life, they drop to around 15% failure rate each year, mostly independent of age. Then, in the old-age phase they seem to ramp up much slower towards death. It's not a hockey-stick right edge, it's more a constant gentle hill slope. We all have seen many drives that are still running after 8, 10, 20 years. In fact, it seems more of a survival of the fittest system (maybe like turtles?), where once they live to a certain age, many go on to live far beyond the average.
Anyhow, my question is, what else in the non-computer world has a failure graph like hard drives? Something easy for a neophyte to grasp. Normal bathtubs have lightbulbs. What analogy can be used for hard drives? I haven't been able to think of any!
Surely there must be one?? _______________________________________________ Roundtable mailing list Roundtable@muug.mb.ca http://www.muug.mb.ca/mailman/listinfo/roundtable
On 2014-09-03 Adam Thompson wrote:
The obvious analogy that for obvious reasons* won't have occurred to you: cars. If you don't get a lemon, it's probably good for a while, but eventually starts to break down. Also, historically, humans - at least in ages and places where infant mortality is/was a significant drag on population growth.
The Cars example is imperfect, because, as you said "it's good for a while", but with hard drives I find that the near-zero-failure part of the bathtub, if it even exists for HDDs, is abominably short, like 6 months. Most quality cars these days (ones ranked high in Consumer Reports reliability) should be nearly trouble-free for 5 years.
Here's my interpretation of the HD curve (monospace required):
| | ____________________________ \ __________/ \ _________/ \ / __/
The main point being that after (maybe) a short reprieve, the failure probability immediately ramps up to and sits at an unacceptable number (like 15%) nearly forever, with but a tiny increment after each additional year. Whether there is a bathtub end after 10-20 years, is up for debate. (Brad and I have Atari ST drives from 30 years ago that still operate, for example.)
Surely if you ASCII'd a modern car graph it wouldn't quite fit?
Your human being analogy is probably much closer to what I'm looking for, but that one definitely has an abrupt bathtub hockey-stick at the right hand side :-) With humans, make it past the first tricky year and you probably have a small chance that stays relatively static for dozens of years of contracting a terminal illness or getting hit by a bus. Not as straight-forward as a "light bulb" example as I was looking for (as it requires some thought and reflection) but pretty good.
Surely, though, in the world of consumer items something else must be just like hard drives?
On 14-09-04 02:23 AM, Trevor Cordes wrote:
The Cars example is imperfect, because, as you said "it's good for a while",
Yup. Closest mass good I could think of offhand.
Surely if you ASCII'd a modern car graph it wouldn't quite fit?
The key difference is that you can repair and maintain a car, whereas a HDD (or SSD, for that matter) is either alive and well, alive and dying, or dead - and there's nothing you can do about it.
Your human being analogy is probably much closer to what I'm looking for, but that one definitely has an abrupt bathtub hockey-stick at the right hand side :-)
Yessss... although not so abrupt, at various points in history.
Surely, though, in the world of consumer items something else must be just like hard drives?
Not that I can think of. You have to combine a) non-negligible failure rate, with b) extremely tight tolerances, with c) variable quality control on (b), to get a similar result. Outside the computing field, I can't think of anything [other than cars] that has as much complexity, as "finicky" as 10,000rpm spinning platters - AND is common enough that everyone will understand it.
I would submit that any device that relies on a hard drive (of which there are many, not just computers), would have a failure curve that closely matches hard drives ;)
On Thu, Sep 4, 2014 at 2:41 AM, Adam Thompson athompso@athompso.net wrote:
On 14-09-04 02:23 AM, Trevor Cordes wrote:
The Cars example is imperfect, because, as you said "it's good for a while",
Yup. Closest mass good I could think of offhand.
Surely if you ASCII'd a modern car graph it wouldn't quite fit?
The key difference is that you can repair and maintain a car, whereas a HDD (or SSD, for that matter) is either alive and well, alive and dying, or dead - and there's nothing you can do about it.
Your human being analogy is probably much closer to what I'm looking
for, but that one definitely has an abrupt bathtub hockey-stick at the right hand side :-)
Yessss... although not so abrupt, at various points in history.
Surely, though, in the world of consumer items something else must be
just like hard drives?
Not that I can think of. You have to combine a) non-negligible failure rate, with b) extremely tight tolerances, with c) variable quality control on (b), to get a similar result. Outside the computing field, I can't think of anything [other than cars] that has as much complexity, as "finicky" as 10,000rpm spinning platters - AND is common enough that everyone will understand it.
-- -Adam Thompson athompso@athompso.net
Roundtable mailing list Roundtable@muug.mb.ca http://www.muug.mb.ca/mailman/listinfo/roundtable
Assuming the hard drive is the least reliable component in the system :P
Sean
On Thu, Sep 4, 2014 at 12:44 PM, John Lange john@johnlange.ca wrote:
I would submit that any device that relies on a hard drive (of which there are many, not just computers), would have a failure curve that closely matches hard drives ;)
On Thu, Sep 4, 2014 at 2:41 AM, Adam Thompson athompso@athompso.net wrote:
On 14-09-04 02:23 AM, Trevor Cordes wrote:
The Cars example is imperfect, because, as you said "it's good for a while",
Yup. Closest mass good I could think of offhand.
Surely if you ASCII'd a modern car graph it wouldn't quite fit?
The key difference is that you can repair and maintain a car, whereas a HDD (or SSD, for that matter) is either alive and well, alive and dying, or dead - and there's nothing you can do about it.
Your human being analogy is probably much closer to what I'm looking
for, but that one definitely has an abrupt bathtub hockey-stick at the right hand side :-)
Yessss... although not so abrupt, at various points in history.
Surely, though, in the world of consumer items something else must be
just like hard drives?
Not that I can think of. You have to combine a) non-negligible failure rate, with b) extremely tight tolerances, with c) variable quality control on (b), to get a similar result. Outside the computing field, I can't think of anything [other than cars] that has as much complexity, as "finicky" as 10,000rpm spinning platters - AND is common enough that everyone will understand it.
-- -Adam Thompson athompso@athompso.net
Roundtable mailing list Roundtable@muug.mb.ca http://www.muug.mb.ca/mailman/listinfo/roundtable
-- John Lange www.johnlange.ca
Roundtable mailing list Roundtable@muug.mb.ca http://www.muug.mb.ca/mailman/listinfo/roundtable
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