Ideally, any moving part will have tear and wear. But when a hard disk is considered, It spins (the spindle that holds the platters) continuously at high speeds literally non-stop, that too at higher temperatures. This goes on for years especially in case of servers. If the spindle assembly gets worn out, say 1/100 of a millimeter, the platters can forcely touch the head. Why doesn't it happen so, eventually lowering the platters to hit the head assembly ?
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Engineers learn from their mistakes?– NickWJun 6, 2013 at 11:41
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3Who said it doesn't? Hard drives die.– terdonJun 6, 2013 at 11:41
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2They die, alot... But they probably do better than expected because of their low tolerance in manufacturing. Perfect balance, vacuum sealed– Austin T FrenchJun 6, 2013 at 13:13
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2Hard disks aren't vacuum sealed. Most have a tiny breath hole that has a specific "do not cover" warning right next to it.– MDMarraJun 6, 2013 at 13:53
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1Most drives are indeed not vacuum sealed and the friction between the platters and the air is a large part of the drives idle power usage. Some high end drives even come with a helium atmospere to reduce this friction.– HennesJun 6, 2013 at 14:32
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4 Answers
Actually, I believe your perception of it is awry. As parts go, when operating under optimal conditions, HDDs have the shortest lifespan of any common component save fans (cause they are cheap) and Power supplies (due to the entropy of all that power). as NickW pointed out, drives have been meticulously designed to operate reliably and accurately, but you are right, due to the mechanical nature of the technology, it is constantly dying slowly as it spins away its life.
answered Jun 6, 2013 at 12:00
You may want to read the GOOGLE white paper "Failure Trends in a Large Disk Drive Population" which studies the failure characteristics of consumer-grade disk drives.
Outside the NSA, Google probably has the largest server/hard drive farm in the world.
The load on the bearings is small; suitably hard metals with sealed lubrication can last that long. Modern drives are transistioning to fluid bearings: see this paper.
Hard drives die all the time. The last job that I had where I was responsible for hardware, we were replacing hard drives regularly. We had approximately 70 servers, some with MD1000 DAS arrays attached, as well as a CX-4 And VNX 5500 SAN. I would estimate that we replaced 2 disks per month on average.
This is why support contracts in servers are so expensive once you get past the standard 3-year warranty. Things die much more frequently in years 4-7.
