Turning off hard drives? Good or bad?

Is it better for my hard drives to be spinning all the time or for them to turn off when not in use?
I'd always thought the latter but a friend of mine asserts that starting and stopping a hard drive will shorten its life-span. That it does more harm than spinning all the time.
Anyone know of data or studies on this?
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There are indeed many arguments and studies regarding this subject, although I've never found any conclusive.
Much depends on the type/quantity/quality of use the HD gets over its life. (ie. video server with a cheap PSU may shorten the life)

The theory behind 'not turning devices off' comes primarily from the heat induced expansion/contraction of cards/chips in sockets eventually working their way partially out of the socket, causing failure or erroneous operating.
Due to the nature of a HDD having many moving parts which can wear out (bearings, motor, solenoids) over time, I suggest this negates the benefits to the controller pcb (and it's components) of being constantly powered on.

The best HD problem prevention is effective monitoring of SMART status, if your motherboard supports it.
Gary CaseRetiredCommented:
You'll find "compelling" opinions on both sides of this argument.   It's good to not overheat the drives, but spinning up is also a stress on the drive motor.  Personally I let the drives spindown after an hour -- when I'm using my computer this almost never happens, but it lets the drives spindown and cool off overnight or if I'm gone.   I also set the drives this way on all the systems I help folks with -- and have outstanding reliability with those systems.

As far as power-related issues with PC's, I think the two most important things you can do are (a) ensure the system has adequate power with plenty of "headroom"; and (b) be sure the system has a UPS ==> systems that are never exposed to unplanned, sudden power outages have FAR fewer problems than those that are.   Doing this will probably have a far greater impact on your hard drives' life than whether or not you set them to spindown.
how786Author Commented:
 Thanks for the 2 replies guys. I'd really like to see the studies. Seagate or WD must have done some research regarding this question.
I'd really appreciate if you could point me to some hard data. Perhaps I will call Seagate in the morning.
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Gary CaseRetiredCommented:
You'll find that hard data is difficult to come by.  What you CAN find if you look at the detailed specifications for any drive are rated start/stop cycles (usually around 50,000 minimum), service life (typically 5 years), and sometimes a very impressive (but misleading) MTBF specification.   The most important specification in terms of this discussion is the rated start/stop cycles.   For example, I just looked up a WD 500GB Caviar (SE16 SATA-II) -- it's rated for a minimum of 50,000 start/stop cycles.   Note that if it spun up once an hour it would be about 6 years before it got to this number!!  (and that's a minimum).   And a drive set to spin down after an hour is unlikely to spin down more than a couple of times a day -- I'd guess mine spins down 1 or 2 times during the day and at night; to be safe I'll say 6 spinups a day -- so I'll reach the minimum rated number in about 24 years !!   I suspect I'll replace my drives before then :-)   And wear from other factors -- heat generation, power-on hours of the spindle motor, etc. will be much lower than it would be if the drive was constantly on.

By the way, notebook drives are designed for far more start/stop cycles than desktop drives, since they are likely to spinup/spindown much more.   Some IBM notebook drives have head load/unload cycle ratings (they use a slightly different technology to store the heads, so this spec is functionally equivalent to start/stop cycles) of 300,000 cycles !!

As I noted earlier, there's really not any hard statistical data -- probably because the drives are so reliable that in almost every case they are replaced before they encounter any problems caused by spinup/spindown cycles.


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I'd also support gary's answer. Generally it is a matter of how often the drives get shutdown, the turned on again. If this happens too often that isn't too good for a disk. It is best that you first know your general usage of the system. If you set the threshold to shutdown to 5 minutes, and you come back after 6 minutes, and that is often the case it is far better not to turn the drive off. When off it should stay off for longer times. It is also stress on you because if you have to wait every 5 minutes for the thing to get ready again, well I'd not appreciate that at all. Also, for the HD powering up it'll need temporarily more power so this, if it happens very often, will also use up more power than if you just keep the disk spinning! So make sure you have at least set the threshold to power off to a long enough period like 1 or more hours.
how786Author Commented:
 Thanks very much.
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