"Unable to unmount volume for repair" - cannot erase, or run first aid, on an external firewire drive
I want to erase my external hard drive, currently full of data from an old computer's Time Machine backups, but I'm not able to...
The drive does mount correctly, I can view files with no problems. I cannot however rename or delete them (e.g. trying to delete a file using Finder gives me an "unexpected error" (code -50); if I go to the Terminal and try "rm" then I get "Invalid argument".
So I went to Disk Utility to run First Aid. If I have selected the Volume and run First Aid then I get the following:
Running First Aid on “LaCieDrive” (disk4s2)
Repairing file system.
Volume could not be unmounted.
Restoring the original state found as mounted.
Unable to unmount volume for repair. : (-69673)
Operation failed…
If, instead, I select the physical device instead of just the volume then First Aid runs just fine, I get no errors.
But I am still not able to erase, because of the unmount problem, regardless of whether I've selected the physical device or just the volume. Looks like this:
Erasing “LaCie Rugged FW/USB Media” (disk4) and creating “LaCie”
Unmounting disk
The volume on disk4 couldn’t be unmounted because it is in use by process 0 (kernel)
Couldn’t unmount disk. : (-69888)
Operation failed…
Final detail: unsurprisingly, ejecting the disk doesn't work. But if I select the "Force Eject" option that does work just fine.
Can anyone help with this?
- The external drive I want to erase is a LaCie "Rugged" 1 TB Firewire drive, currently with GUID partition map and formatted as Mac OS Extended (Journaled).
- The laptop from which I'm running Disk Utility is a MacBook Air (M1, 2020), using Mac OS 11.3.1.
