Unable to resolve unmounting disk error to reformat My Passport

Hello, ariadnefromrhinebeck.

To start off, have you tried repairing the disk? If not, try that next: Repair a storage device in Disk Utility on Mac - Apple Support. Follow these steps:

1. "In the Disk Utility app on your Mac, choose View > Show All Devices. If Disk Utility isn’t open, click the Launchpad icon in the Dock, type Disk Utility in the Search field, then click the Disk Utility icon. Note: If you’re checking your startup disk or startup volume, restart your computer in macOS Recovery, select Disk Utility in the macOS Recovery window, then click Continue. If you check your startup volume (Macintosh HD), make sure you also check your data volume (Macintosh HD - Data).
2. In the sidebar, select a volume, then click the First Aid button.
3. In the First Aid dialog, click Run, then follow the onscreen instructions.
4. When the First Aid process is complete, click Done.
5. Repeat steps 2 through 4 for each volume on the storage device.
6. In the sidebar, select a container, then click the First Aid button.
7. In the First Aid dialog, click Run, then follow the onscreen instructions.
8. When the First Aid process is complete, click Done.
9. Repeat steps 6 through 8 for each container on the storage device.
10. In the sidebar, select the storage device, then click the First Aid button.
11. In the First Aid dialog, click Run, then follow the onscreen instructions.
12. When the First Aid process is complete, click Done."

Let us know if we can help with anything else at all or if this doesn't settle your issue. Thanks and have a fabulous day!

I've gotten that message several times. What I've done is manually eject the drive by dragging it to the Trash bin. Then I go back to Disk Utility, select the drive and erase it. That worked for me every time.

But erasing should be the last ditch effort. Try to fix it as Chris_D13 suggested.

Hi ariadnefromrhinebeck,

You don't have to, but it might help with what you're trying to accomplish. If you try this step and the issue remains, then you'll want to reach out to Apple Support to have this looked into further.

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