I have a very odd issue with my external USB3 hard drive. Sometimes, I can use it with no problems, but sometimes it slows down the entire computer and freezes processes.

For example, spotlight might stop working, and if I kill it through the Terminal, no new spotlight process launches. And for example the dock might freeze, not responding to anything and just showing a beach ball when I put my mouse on it. Same thing with Finder.

Some things still work but the more I use the computer with the hard drive in, the more processes freeze, for example if I quit Safari I can't open it again. However, if I just unplug the cable suddenly every single process starts responding/working again instantly, with no problems.

I have tried to repair my hard drive through Disk Utility, but it finds no problems.

  • " if I just plug the cable" - if you plug the cable in or if you unplug it?
    – oa-
    Commented Apr 19, 2017 at 12:20
  • Spotlight indexing may be hammering the drive. You might want to experiment by excluding this external drive from being indexed by Spotlight. Go to System Preferences > Spotlight > Privacy tab and either drag or add the external drive with the "+" icon. This will force Spotlight to ignore the drive. If the computer no longer freezes, that's the problem.
    – IconDaemon
    Commented Apr 19, 2017 at 12:51
  • @oa-, sorry I meant unplug. Commented Apr 19, 2017 at 13:11

1 Answer 1


This is a common issue with mechanical HDDs (non-SSD).

macOS sends a command to the external device (your HDD) but the device responds slowly. Some HDDs need to spin up in order to respond to the OS's request. Until the device is able to respond the OS may freeze.

To improve your system's performance try these steps:

  • prevent HDD sleep. Spinning the HDD down may save some energy but it slows down your system as well.
  • Disable Spotlight for the external drive. System Preferences > Spotlight > Privacy > "+". Select your external HDD and press "Choose".
  • This has been happening to me, even with no audible hard disk activity. It's just sitting there, freezing processes and such, until I forcefully unplug the cable.
    – Alexander
    Commented Jul 27, 2019 at 0:44
  • How can I prevent HDD from sleeping?
    – alper
    Commented Dec 16, 2020 at 0:01

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