Is it possible to manually put an external hard disk to sleep? Right now, I've already got "Put the hard disks to sleep when possible" checkmarked in the Energy Saver preference pane, and so they should sleep after 10 minutes of inactivity, but I'm wondering if it's also possible to do this manually whenever I want.

I just bought an external hard drive and it's already spinning constantly, compared to my current external which is completely quiet, so I'm wondering if I can put it to sleep when I need to to stop it from spinning all the time.


Not an exact answer to your question, but when using Terminal.app there is an option to even further reduce hard disk sleep time from 10 minutes to 1 minute, with this command:

$ sudo pmset -a disksleep 1

On macOS, there's isn't a way to do so from the command line. To put your drives to sleep (aka spin down) you need to send an ATA command to the drive. This becomes problematic when trying to do this to USB drives because it would be dependent on what the USB to ATA bridge (controller in/on the USB enclosure/interface, not in the Mac) was capable of supporting (this is also why you can't reliably get SMART status from USB drives).

  • In Linux, you can use the hdparm -Y /dev/sdX
  • In Windows, there is an app called RevoSleep
  • BSD has the atacontrol and camcontrol utilities to send ATA commands
  • SpindownHD was a utility with Apple's CHUD tools, but it's last release was in 2006

Unfortunately, at current for macOS, there is nothing that allows sending ATA commands directly to drives. It would need to be embedded into something like diskutil or a 3rd party app to get the functionality you are looking for. Though (IMO) it's unlikely because with the increasing prevalence of SSDs, there's really no more need to "spin down" a drive.

For more info, see this post on SuperUser: Ways to shut down/sleep and wake up hard drives on command?

Your best bet is to either eject the disk or set the sleep timer to 1 minute.

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