External disk could not be unmounted because of process 58

I am trying to change the format of my Lacie external hard drive from MacOS Extended Journaled to APFS so that I can store my OneDrive files. I keep getting unmounting errors. Here is a screen capture of the error. The drive is connected to an iMac running the latest Big Sur. Suggestions?

iMac Line (2012 and Later)

Posted on Feb 12, 2021 3:50 PM

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Posted on Feb 12, 2021 4:28 PM

Boot into Safe Mode by booting with the Shift key held down and erase the hard drive from there.  Then reboot normally.


NOTE: Safe Mode boot can take up to 10 minutes as it's doing the following; 

• Verifies your startup disk and attempts to repair directory issues, if needed

• Loads only required kernel extensions (prevents 3rd party kernel/extensions from loading)

• Prevents Startup Items and Login Items from opening automatically

• Disables user-installed fonts 

• Deletes font caches, kernel cache, and other system cache files


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Question marked as Top-ranking reply

Feb 12, 2021 4:28 PM in response to Christina Frain

Boot into Safe Mode by booting with the Shift key held down and erase the hard drive from there.  Then reboot normally.


NOTE: Safe Mode boot can take up to 10 minutes as it's doing the following; 

• Verifies your startup disk and attempts to repair directory issues, if needed

• Loads only required kernel extensions (prevents 3rd party kernel/extensions from loading)

• Prevents Startup Items and Login Items from opening automatically

• Disables user-installed fonts 

• Deletes font caches, kernel cache, and other system cache files


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External disk could not be unmounted because of process 58

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