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On a Macbook Pro M1 with MacOS Monterey 12.5.1, I have an external 2.5" USB hard drive that I use regularly. When done using it, naturally I eject the volume by dragging it to Trash. This unmounts the volume but the disk remains physically spinning. Since this drive is powered by USB, when I then unplug the USB cable, it loses power while still spinning.

I understand that modern drives handle this without damage, and that myths about the utter necessity of "parking" a disk are based on the hardware of 40 years ago. However, I believe I have read that drives are rated for a much smaller number of these "emergency" spin-downs over their lifetime, compared to power-off with the drive already spun down, and power-off retract count is a specially tracked statistic in S.M.A.R.T. data (0xAE or 0xC0). So my understanding is that, for longevity, it is still preferable to spin down the drive before unplugging. How do I do that?

GUI preferred but command line would also be okay. Under Linux I would do udisksctl power-off but that command does not exist under MacOS.

There are several questions on this site about spinning down drives when idle, and how to set the timeout, but that wouldn't really help me unless I was to wait for the timeout after unmounting.

To be clear, if possible I'd rather not change spin-down times or other behavior in general. I'm happy with the way the drive spins up and down while in use. I just want to be able to spin it down after unmounting, or immediately upon explicit request. Again, an exact equivalent of Linux udisksctl power-off would be ideal - you issue the command, the drive spins down right away, and its settings are otherwise unaffected.

The linked "duplicate", if I understand it correctly, is about spinning down a drive while keeping it mounted (so that it would automatically spin up when accessing again). Here I want to spin down a drive that has already been unmounted, and that will not be mounted again before the drive is disconnected, so I don't think this is a dupe. And in fact I did find a simple solution that is specific to that scenario (only works when unmounting the drive), so if this question is reopened I can post it as an answer.

Nate Eldredge
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  • You need to specify your hard drive model. Most drives have a automatic head parking and spin down. But times are model dependent. I don't think there is any way to alter these values with macOS or to force a spin down. – Gilby Aug 24 '22 at 05:18
  • Why drag to the trash? I select the drive / usb and cnd+E does eject. – Solar Mike Aug 24 '22 at 07:12
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    @SolarMike - drag to Trash has been 'Eject' since the first Macs with floppy drives. It's only been Cmd/E since OS X, prior to that it was Cmd/Y, for 'Put Away'. Some of us have been using Macs a long time ;)) – Tetsujin Aug 24 '22 at 07:33
  • @Tetsujin I'm sure I have my backup of system 7 around... not that I will use it. And used it as an emulated machine on an Atari 1040ST - which I did my final year project on. – Solar Mike Aug 24 '22 at 07:35
  • @SolarMike: Yeah, I'm showing age here. I just got this Mac recently, and otherwise haven't really used Macs at all since the early '90s, so much of what I do is based on vague memories... Good to know about Cmd/E, though, so thanks. – Nate Eldredge Aug 24 '22 at 12:48
  • @Gilby: Well, with udisksctl on Linux I don't need to worry about a timeout at all. I issue the command and the drive spins down immediately, simple as that. Any timeout settings are otherwise unaffected, and it works with all drives I've ever tried including this one. So ideally I'd like an equivalent of that. But I will add drive model information when I can (don't have the drive in front of me just now). – Nate Eldredge Aug 24 '22 at 12:51
  • Are you certain that "emergency stop" means what you think it means? Maybe it's when the Sudden Motion Sensor kicks in, as in when you drop the drive. I don't see how pulling the USB cable is any different from switching off an external HDD enclosure that has a physical switch after unmounting it, like we did for years before external drives got small and power-efficient enough to use bus power. So you might be trying to account for a problem that isn't actually a problem. – Kevin E Sep 23 '22 at 16:06
  • I flagged as a dupe because spinning down a drive is dependent on the USB to SATA interface; most don’t provide the capability to receive the command from the OS. For Apple, it’s a moot point as Apple provides no way for the user to send the command. It still apples to the new Apple silicon Mac computers. – Allan Jan 21 '23 at 15:51

2 Answers2

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I did eventually stumble on a way to accomplish this. (Now on Ventura 13.4.)

Open the Disk Utility application and from the menu, select View : Show All Devices (⌘ Command 2). In the sidebar under External, in addition to your volume(s), you should now see a top-level item for the drive itself, with a name like "WD My Passport 1234" (i.e. something set by the hardware, not a volume name that you created). Click the Eject icon next to this entry. It will unmount and eject all volumes contained in this drive, assuming they are not in use, and then it should spin down the drive.

It would be interesting to know if there is a command-line equivalent.

Nate Eldredge
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  • It’s no longer necessary to spin down a drive or park heads. Engineers have accounted for hot plugging drives for decades now. To eject from the command line issue the command diskutil eject <mount>|<device> – Allan May 29 '23 at 12:19
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The spinning of hard disks can be altered in System Preferences.

Choose the Energy Saver pane.

In that there is an option "Put hard disks to sleep when possible" and check that on.

Energy Saver Pane

mmmmmm
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  • Well, I don't particularly want to spin it down at every possible time. Only on request, after I have unmounted it and am ready to unplug. I suppose I could umount the drive, turn this option on, wait for it to sleep (not clear how long that would take), disconnect it, and turn the option back off, but that's pretty awkward. – Nate Eldredge Aug 24 '22 at 12:43
  • Nonetheless, I'll try this and see if it works for me - maybe I can live with some extra spin-downs in exchange for desired behavior. So thanks for the suggestion. – Nate Eldredge Aug 24 '22 at 13:02