External NTFS drive won't mount on macOS ("Volume is corrupt")
Symptom Drive shows "Volume is corrupt" / $MFT I/O errors / "Unrecoverable error"; ntfsfix and ntfs-3g both fail to mount it.
A 1.5 TB USB NTFS drive suddenly refused to mount on macOS. Every Mac-side tool made it look like the disk was dying: Disk Utility reported “Volume is corrupt,” mount_ntfs logged $MFT I/O errors, and both ntfsfix and ntfs-3g -o ro,recover,force bailed with an “Unrecoverable error.” It looked like a job for ddrescue and a new drive.
It wasn’t. The drive was fine.
Root cause
The volume was formatted with a 64 KB NTFS cluster size. The macOS NTFS stack — mount_ntfs, ntfs-3g, and the macFUSE driver underneath them — handles large clusters poorly. When it can’t walk the Master File Table the way it expects, it reports the failure as catastrophic corruption even though the on-disk structures are intact. The symptoms are loud and scary and almost entirely misleading.
The fix
Don’t repair it on the Mac. Repair it on Windows, where the native NTFS driver reads 64 KB clusters without complaint:
chkdsk X: /f/f fixes the filesystem (the index and $MFT references the Mac driver tripped on). After chkdsk completes, the drive mounts on the Mac again immediately.
What didn’t work
ntfsfix /dev/diskNsM— exited with an unrecoverable error.ntfs-3g -o ro,recover,force— same.- Disk Utility First Aid — declared the volume corrupt and stopped.
All three were dead ends because the problem was the driver, not the disk.
Aftermath and the real lesson
This drive corrupts repeatedly under the macFUSE NTFS driver — not a one-off. On later mounts it has produced orphan found.000 folders full of zero-byte metafile stubs, and once degenerated a whole directory into a 0-byte file with exec bits (Finder opened Terminal instead of the folder — classic NTFS directory-index corruption).
The durable fix is operational, not technical: treat a macFUSE-mounted NTFS drive as a cold archive only. Keep authoritative work on native-filesystem storage and use the NTFS drive purely for backups you can afford to re-create. When it does corrupt, chkdsk /f on Windows is the reliable repair — reach for it before assuming hardware failure or jumping to ddrescue.