Fix Guide: Sequoia External SSD Read-Only Fix

Symptom: Your external USB-C or Thunderbolt SSD suddenly becomes "Read-Only" on macOS Sequoia, even though it was working fine before and isn't physically locked.

Why this happens

macOS Sequoia has introduced stricter checks for APFS and ExFAT volumes during the mount process. The fsck_apfs or fsck_exfat utility (triggered by diskarbitrationd) may flag the drive as "unclean" if it wasn't ejected perfectly. Instead of failing to mount, Sequoia mounts it in read-only mode to protect the data. This is often managed by the com.apple.storagekitd daemon which fails to clear the "dirty" bit on the drive's metadata.

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Fix 1: Force an Unmount and Manual Disk Repair

Using the command line bypasses the Finder's safety locks and allows for a more aggressive repair.

# List drives to find your identifier (e.g., disk4s1)
diskutil list
# Force unmount the drive
diskutil unmountDisk force /dev/diskX
# Run a manual repair
sudo fsck_apfs -y /dev/diskX

Fix 2: Reset the Disk Arbitration Daemon

If the system is stuck in a loop thinking the drive is busy, restarting the management daemon can help.

# Restart the disk arbitration daemon
sudo killall diskarbitrationd

Fix 3: Clear the mds-store index on the drive

Sometimes the mds (Spotlight) daemon hangs while trying to index the drive, which causes the system to lock it as read-only to prevent index corruption.

# Disable spotlight on the external drive
sudo mdutil -i off /Volumes/[DriveName]
# Remove the metadata folder
sudo rm -rf /Volumes/[DriveName]/.Spotlight-V100

Recommended Tool: CleanMyMac

Disk permission errors and hidden "Spotlight" or "Trash" bloat on external drives are a common cause of read-only issues. CleanMyMac’s "Maintenance" module can "Repair Disk Permissions" and "Thin Time Machine Snapshots" that might be locking your disk's partition table.