I have a Drobo 5N NAS with 3 x 1 TB HDD's (2 x SATA 5400 RPM + 1 x SATA 7200 RPM), and I just replaced its fan but was stupid enough not to test it before reassembling. When I turned on the NAS, the fan didn't start, and it reported one of the HDD's missing. It turned out I didn't properly insert the HDD, then when I did, it started rebuilding. It's already running for almost an hour now, and it says there are still 3 hours remaining.

I wish I could just shut it down and try to fix the defunct fan, but if I do that in the middle of rebuilding, I risk losing data, however, an overheating HDD may fail too, so that could lead to losing data as well.

I was wondering, are these 3 HDD's, stacked one above the other, with a few mm's and a layer of metal between them, supposed to withstand the heat they're producing in about 4 hours or is there a potential they'd break before the rebuilding finished?

  • It appears that fan cools the CPU heatsink as well, so that might overheat before the drives do.
    – Jason
    May 29, 2019 at 23:19

1 Answer 1


There are too many factors for anyone to provide you a definitive answer.

Hard disk manufacturers publish temperature ranges in which the disks should be operated. It's reasonable to assume that over short periods of time one could operate outside these ranges without the drives dying. But this is a gamble and hard to know for sure.

It's important that the drives are exposed to some air flow. At minimum, convection of warm air away from the drives should be possible. Take steps to ensure fresh, cooler air can get to the drives. If possible, get a portable fan and aim it at your NAS. You could also kick on air conditioning if that's an option.

  • Will an average hair dryer (on lower setting, the high one is too noisy and people are sleeping next door) do the trick, you think, or would you just not worry at all? I don't plan on leaving them on without a fan after the rebuild finished, and it's around 21-22 degrees Celsius in here. There is just one thing that worries me a little and that is the fact that they are close to each other and may heat each other too much...
    – benomatis
    May 29, 2019 at 22:08
  • The hair dryer (not set to heat!) would be fine, though if the drives are well exposed to the surrounding 22 C air you're fine. I stack multiple mechanical drives (loosely) while running and don't worry about that at all. May 29, 2019 at 22:11
  • They are a few mm's apart with a metal layer between them and are in a relatively thin layer of metal enclosure on the side, while their backs and fronts are mostly open
    – benomatis
    May 29, 2019 at 22:21
  • @webeno, drives often go in enclosures without fans, like to make USB drives. Drives aren't huge generators of heat. Can you prop it on end so the front and back are facing up and down (either way)? Then the heat will create an air current through the enclosure. If the enclosure is metal, it will also radiate heat. The fan may not be all that important.
    – fixer1234
    May 29, 2019 at 22:52
  • interestingly it stopped rebuilding, so I took it apart, and am now testing the fan... which is only starting when I turn the device off :) so now I have a new problem to fix...
    – benomatis
    May 29, 2019 at 23:16

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