Why won't my USB drive power down on eject? I've just upgraded from High Sierra to Mojave. I have a Lacie Porsche USB-C drive that I use for Time Machine backups. In High Sierra when I ejected the drive, it would power off and I could safely unplug it. However, now it doesn't spin down and I can't safely unplug. All I can do is put my Mac to sleep which in turn powers down the drive.

I have tried excluding the drive from Spotlight indexing and even disabling indexing altogether but this hasn't helped.

Anyone else having this problem or have a solution?
Use this Terminal command  sudo lsof | grep DODO

to find out who is using the USB.

Wait for it to respond, it might take 10 seconds.

If no one is using it, it is safe to eject the disk (pull out).

I did not answer your question "Why it does not Power Down" ? I do not know, probably missing the handshake saying I am done.