My 500GB external hard drive (Networx USB-C) is no longer readable on macOS Tahoe.
Disk Utility detects it but can’t repair it.
First Aid reports APFS verification errors and an invalid object map as follows:
error: (oid 0xd665e) om: invalid o_xid (0x193fb)
error: verification/reading of the omap object failed: Illegal byte sequence
How can I regain access to the drive’s contents?
That “invalid object map” error means your APFS metadata is corrupted — pretty common when an external drive disconnects mid-write.
Disk Utility can’t fix this kind of low-level issue. Don’t reformat it yet if the data matters!
Here’s what you can try first:
- Open Terminal and run diskutil list to confirm the disk identifier (e.g., disk4).
- Try mounting the container manually. (Replace the disk identifier of your drive’s)
sudo diskutil mountDisk /dev/disk4
Sometimes it mounts read-only, which is enough to copy data off.
If that fails, use a third-party recovery tool, like iBoysoft Data Recovery for Mac, to scan the APFS drive. Meanwhile, use this tool to recover data from the external hard drive.
Download iBoysoft Data Recovery for Mac
If even the data recovery software can’t detect the APFS drive, the corruption is at the container or hardware level. In this case, you need professional recovery. Once your data’s safe, reformat the drive completely using:
diskutil eraseDisk APFS EXTERNAL /dev/disk4
Replace disk4 with the actual identifier of your APFS drive.
That should get it working again.
Ugh, I’ve seen this a few times since upgrading macOS. In my case, the drive wasn’t actually dead. The enclosure was flaky. If you have another USB-C cable or adapter, try that first. Sometimes just changing ports or using a USB-A adapter works.
If it’s still not readable, it’s probably a corrupted APFS volume. Recover data from it with professional data recovery, as the user mentioned above - iBoysoft Data Recovery for Mac, and then reformat the drive.