External drives · Mounting and drive problems
What should I do if First Aid can't repair my external drive?
Short answer: Copy everything you need off the drive while it still mounts, stop writing to it, then erase it and run First Aid again. If errors return on a freshly erased drive, the hardware is likely failing and should be replaced.
Treat the drive as untrustworthy: copy everything you need off it now, while it still mounts, then erase it and test it before trusting it again. A file system that First Aid can't repair can lose more data the longer you keep writing to it.
Steps:
- Don't write anything new to the drive. Close apps using it.
- Copy your important files to another drive. If the drive is read-only after the failure, copying off it still works.
- Erase the drive in Disk Utility (select the top-level device, Erase, APFS), then run First Aid again.
- If errors return on a freshly erased drive, the hardware is likely failing — replace it.
If the drive held things Storage Studio moved, see what to do when your fast drive is failing before erasing anything, so you bring those items back first.