mac first aid unable to unmount volume for repair

When I attempt to run the First Aid, I get the following: Repairing file system, Volume is already unmounted.

OLD external drive, had its own power source, plugged into a surge protector.

I hit the power button on the surge protector when I was unplugging something else, and the drive was turned off while in use.

I turned it back on and it sounded normal, but my computer wasnt recognizing it, and Disk Utility wouldnt load when it was plugged in.

I tried restarting with and without the disk, mounting, unmounting, all of the above recommendations.

I finally found a suggestion to see if fsck was holding the disk hostage.

A quick ps aux grep fsck revealed that indeed it was hijacking the diskvolume as soon as it was plugged in.

Though the volume now is read-only and the system suggest to format it as soon as possible, at least i could copy all the content.

I had to repeat this process after ejecting since the drive wont mount.

I ended up repairing the disk (formatted exFat) and it went back to working as normal.

Thanks And shame on Apple (Mac Os) for not providing some type of feedback if fsck is running.

If so, you will need to format your hard drive, through the steps found here, along with the man page obtainable through man diskutil if you need more information.

After mount in readOnly mode, I have ejected with finder and physically remove-plugin usb cable again: it works.

Go to Launch Pad, Disk Utility, and select the disk that wont mount.

Ejected the external hard disk properly from the Windows PC and plugged it to my Macbook.

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Mac First Aid Unable To Unmount Volume For Repair