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External hard drives can't mount after upgrading to Sonoma

My 2023 Silicon Mac Mini recently upgraded to Sonoma, and since then, none of my USB-A devices have mounted successfully or at all. These disks are encrypted with APFS. When I first started, none of them were present, and I couldn't mount them in Disk Utility either. I attempted recovery mode, as suggested by the tip. Disk utility can be used to mount them even when they are grayed out in recovery mode. I have a Time Machine drive that has remained visible on reboot, but another drive is gone. However, they frequently disappear again after a standard reboot. That this OS has such a basic flaw is quite frustrating.

Best Answered by

Amanda Wong

Answered on Tuesday, August 27, 2024

As you can mount the drive in macOS Recovery Mode but the drive is not showing up in a standard boot, the login items, disk errors, and third-party software could be the culprit.

The reasons are various when external hard drive is not mounting on Mac Sonoma, you should identify the possible causes, and troubleshoot the issue step by step. There shouldn't be a connection issue as it can be mounted in macOS Recovery Mode, then, here is what you can try:

  • Repair the not mounting drive in Disk Utility in Recovery Mode.
  • Boot Mac into Safe Mode to check and repair errors.
  • Check and move Login Items that could cause the drive not to mount.
  • Uninstall suspicious third-party apps that may prevent the drive from mounting.
  • Recover data from not mounting the drive and reformat the drive.

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