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Storage Array - Spin down drives or keep them spinning?

Posted on 2009-05-12
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I'm setting up a 5Tb storage array using 6x Western Digital WD10EADS 1TB drives in RAID5.

Usage of this array during the day is intermittent. If I set them to spin down after an hour, they will spin up and down a few times a day. In addition, they will spin up once at night while automated backups are being performed.

Should I set these drives to spin down when not in use or leave them spinning? My main concern is reliability. Does the mechanical wear from spinning 24x7 exceed that of spinning up and down a few times a day, and what of the thermal stress from spinning up/down?

Power consumption is not an issue as they only consume 2.8w while spinning idle.

I'd love to hear from anyone that has some insight into failure rates related to the above usage scenarios.
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Question by:satellite428
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garycase earned 500 total points
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You'll get a variety of opinions about this, but I'll toss in mine ...

=>  Modern drives are typically rated for a minimum of 50,000 spinup/spindown cycles ... often significantly more than that.   With a few spinup/spindown cycles per day, you're not likely to come anywhere close to that within a typical drive's lifetime ... so it's very unlikely to impact the drive's reliability.

=>  Thermal cycling isn't an issue as long as the drives are well-ventilated and don't get excessively warm during typical operations.

=>  As a counterpoint, it's also not a problem if you simply leave the drives on, as long as they're very well ventilated (I'd expect temps in the low 30's ... or may even the high 20's if the room is cool enough).

Bottom line:   There's no set rule about this ... and a variety of opinions.   Personally, I have all my drives set to spin down after an hour, and have drives as old as a decade that still work perfectly.   That includes my desktop systems, a couple of HTPCs, and a 12TB storage server.     FWIW, Western Digital sets their MyBook external drives to automatically spin down (I've not timed them; but it's less than an hour) ... so when they have control of the process, they choose spindown :-)
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by:drewha1969
ID: 24366891
Scott Mueller once calculated (in Upgrading and Repairing PCs)  that the costs of continuously running a PC will be more expensive than buying the hardware parts that fail...  So from a costs view, it depends on how critical it is to have the machines available 24/7.

With that said, it was also noted that hard drives usually will last longer if they are kept running continuously.

It all boils down to how much can you afford to be down and how much you are willing to pay.
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by:Callandor
ID: 24366971
Since there are no clear-cut advantages to doing one or the other from a technical perspective, are there any pressing non-technical reasons that might play a role, such as an important person randomly needing access very quickly?  If so, let the users' patterns of access determine the strategy you choose.
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by:andyalder
ID: 24368672
What is the duty-cycle on these disks? Using them intermittently is to be encouraged, they are not designed for 100% duty cycle, more like 30% so you might as well spin them down when idle. The controller can't do a background parity check on them if they are spun down of course, but if you backup regularly that doesn't matter much.
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by:satellite428
ID: 24371543
Thank you for the replies. It does seem as though there is no hard data supporting one strategy over another. WD would no doubt have the data, but I don't see them releasing it any time soon!

Interestingly, I found the following nugget of information regarding disk temperature vs probability of failure:

http://en.wikibooks.org/wiki/Minimizing_hard_disk_drive_failure_and_data_loss#Temperature_monitoring

The cooler it is, the higher the probability of failure! The ideal temperature range seems to be 37 °C to 46 °C.
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by:garycase
garycase earned 500 total points
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I've seen similar studies ... but remember these are for operating (e.g. spinning) drives. The lesson is to not "overcool" a drive => note that 27°C (below which the failure curve starts climbing rapidly) is only 80°F ... just a few degrees above ambient for a normal room. To keep a drive below that when spinning, the ambient temperature would have to be very low; the airflow would have to be very high; or some combination thereof ... which could easily result in conditions that would result in moisture in the drive's electronics.

Further, note that a spindown is not a full power cycle => the drive's electronics are still on and ready to spinup the platter on demand ... this will tend to keep the drive's temperature in the high 20's (my storage server temps are typically ~ 28°C immediately after spinup ... and stabilize in the mid-to-upper 30's. Temps in the upper 40's are not desirable ... I'd argue against the 46°C upper end of the range you quoted above. For a drive that's simply left spinning 100% of the time, I'd like to see a range of about 38-42°C ... but for non-enterprise drives that aren't designed for 100% duty cycle, I still think a modest spindown time (an hour is a good setting) is the best approach.
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