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I have a 4TB WD external hard drive with three partitions on it, one being a Time Machine partition. When a Time Machine backup is running and the computer goes to sleep, it triggers a few different annoying issues.

First, I can no longer seem to eject the partitions properly. I get an error saying that the drive is in use. The application What’s Keeping Me? tells me that mds and its related processes are keeping the drive from unmounting, but no matter how many times I kill the processes they return and makes it impossible to unmount.

Second, it seems that the drive will continually mount and unmount during sleep, which is terrifying. When I open the computer again, I see a whole bunch of notifications that I manually have to dismiss (Norwegian OS in the image).

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Third, Time Machine gives me an error saying it couldn’t complete the backup, and I have to force an unmount and replug the drive for it to work properly again.

I’ve excluded Spotlight from indexing the external drive, excluded Time Machine from backing up the other external partitions, there is no sleep timer on the WD drive itself, but Power Nap is enabled. What should I do?

Edit: ‘Put hard drives to sleep when possible’ is unchecked in System Preferences.

  • Well, one thing is to set your computer to not sleep forever, by going into System Preferences -> Energy Saver -> and drag the slider all the way to the end – An Existing Person Jun 10 at 17:31
  • @AnExistingPerson That’s kind of suboptimal though, isn’t it? I’d like to use the features of the OS… – Simon Jun 10 at 17:39
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To answer my own question:

Most likely the issue was caused by the WD Driver Utility app, as reported by many in the WD forums.

If not that, it was caused by an unpowered 7x USB-A to USB-C hub that the HDD was connected to earlier.

Either way the problem is now gone.

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