MacBook Pro: External drive lost read/write after First Aid

This isn’t a permissions issue at all, it’s the filesystem getting flipped into a forced read-only state. When Disk Utility says it “couldn’t unmount” the drive and then finishes First Aid anyway, macOS often mounts that volume read-only to avoid further damage.

At that point, Finder permissions become meaningless, you can tick Ignore ownership all day and it won’t change anything because the kernel has already decided the filesystem isn’t safe to write to. This is very common on older external HDDs, especially if they’re HFS+ and have minor catalog or journal corruption.

First thing I’d do is run diskutil info /Volumes/YourDrive in Terminal and check if it explicitly says “Read-Only Volume: Yes”. If it does, try diskutil unmountDisk force /dev/diskX followed by a First Aid from Recovery Mode, not normal macOS, because the OS can’t repair a mounted filesystem properly.

If Recovery First Aid still leaves it read-only, stop trying to fix it in place and immediately image or copy the data off while it still mounts. Reformatting will “fix” it, but only because it wipes the damaged filesystem. The key takeaway, First Aid didn’t break permissions, it detected structural issues and macOS locked the drive to protect your data.

royksjr wrote:

Hi

Using an old MB Pro on vacay, out of curiousity I ran Disk Utility First Aid on a 3 year old storage drive that had been functioning perfectly. First Aid couldn't unmount the HDD, and afterwards said the drive couldn't be used to write on.

Why not, it was working perfectly fine till I ran First Aid, so I went to Get Info for that drive and saw that I have permision to Read & Write, Staff does too, but Everyone does not.

Thinking I'd been relegated to Everyone, I tried changing it to Read & Write but got the msg I didn't have permission. I checked "Ignore ownership on this volume," no help.

What can I do to regain permission to Read & Write?

Royks

You can try reformatting the drive as new...and compare your results. Of course this wipes all data.

All drives will fail in due time, not if but when.

erase/ reformat/ initilize as new the top most parent drive (View>Show All Devices)

Erase and reformat a storage device in Disk Utility on Mac

Erase and reformat a storage device in Disk Utility on Mac - Apple Support