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Verified for macOS Tahoe 26.2

How to Fix External Drive Read-Only Error in macOS Sequoia 15.x

Symptom: You connect an APFS or ExFAT drive to macOS Sequoia, and it mounts as "Read Only," even if the permissions are set correctly.

TL;DR fix

Start with Fix 1: Force Unmount and Repair. If the issue persists after that, try Fix 2: Clear Disk Arbitration Cache. Full Terminal commands and step-by-step instructions are in each section below.

Why this happens

Sequoia has stricter "System Integrity" checks for external volumes. If the drive wasn't ejected properly, the 'fsck' (file system check) flag may lock the volume to prevent data loss.

Recommended Troubleshooting Tool

Before proceeding with manual fixes, we recommend using CleanMyMac X. Quickly identify high CPU apps and optimize system memory with one click.

Fix 1: Force Unmount and Repair

  1. Open Terminal.
  2. Find your drive's identifier:

diskutil list

  1. Run the repair (replace disk4s1 with your ID):

sudo diskutil repairVolume /dev/disk4s1

Fix 2: Clear Disk Arbitration Cache

  1. In Terminal:

sudo killall diskarbitrationd

  1. Re-plug your drive.

Recommended Tool: Paragon NTFS for Mac

If you frequently work with Windows-formatted drives:

- Get Paragon NTFS to ensure seamless read/write access on macOS without the stability issues of native experimental drivers.

Tested and documented by the MacDebug team — about MacDebug. See also Photoshop & Adobe Apps Crashing on macOS Tahoe, Fix macOS "No AirPlay Found", or browse all guides on macdebug.