External drive won't eject cleanly I have several external drives, all of which work fine, but recently purchased and backed up to a new drive (Samsung T5) which always fails to eject cleanly. Whenever I try to eject it, I'm asked:

“Drive” is a volume on a disk that has 2 volumes. Do you want to eject “ Drive” only, or both volumes?
To eject both, click Eject All, or hold down the Option key while ejecting.
To eject only “Drive,” click Eject, or hold down the Control key while ejecting.

Unless I choose Eject All, the drive stays around, so I choose Eject All. But then I get a message that says &quot;Drive - Data&quot; was not ejected because it was in use, and I have to Force Eject to finally eject it. When I then unplug the drive I get a warning that doing so might have caused problems.
There's nothing that I know of that's actually using the drive when I do this, and no damage seems to be done.
Why won't my Samsung T5 eject cleanly?

The drive is formatted APFS/GUID, unencrypted and is a bootable clone with FileVault enabled (though it behaved this way before FV was enabled too, and before anything was backed up to it.)
This issue is generally caused by a background process that is taking a (very) long time to complete. 

In my case it was Spotlight indexing, which I don't need for the drive in question. So after confirming that it the culprit was indeed Spotlight and terminating it, I simply disabled Spotlight indexing for the drive, and now I am able to eject cleanly. Similar instructions apply for identifying and terminating whatever process is the cause generally.