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External hard drive not mounting Mac

After upgrading from OS X Sierra to OS X High Sierra on my MacBook Air, I can no longer mount and read my external hard drive. During the upgrade, I converted my MacBook hard drive to APFS. My external drive is formatted as Mac OS Extended. Is the data on my external drive inaccessible now that I have APFS on my computer? Or is there a way to access it?

Best Answered by

iBoysoft author Eudora Liu

Eudora Liu

Answered on Wednesday, November 26, 2025

To fix your external hard drive not mounting on your MacBook, you can recover your data from the unmounted external hard drive first. iBoysoft Data Recovery for Mac can help you to solve this problem.

iBoysoft Data Recovery for Mac has a good algorithm that can help you to recover data from an unmounted external hard drive. Here's how:

Step 1: Free download and open iBoysoft Data Recovery for Mac.

 Download

iBoysoft Data Recovery for Mac

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Step 2: Choose the unmounted external hard drive and click Search for Lost Data.

Step 3: Find and preview the search result.

Step 4: Choose a location to restore your data and click Recover.

After you recover your data, you can fix the unmounted external hard drive by using First Aid in Disk Utility to fix it and mount it on your Mac again.

  1. Go to Launchpad > Other > Disk Utility.
  2. Click the unmounted external hard drive and click First Aid on the top menu.
  3. Click Run to start the process.

If there's any problem, it will be fixed automatically; if not, you need to take another way--format the external hard drive in Disk Utility to fix it. You can take the steps as follow:

  1. Click Erase in the top menu in Disk Utility.
  2. Type in the disk name and select a format and a scheme.
  3. Click Erase to start.
  4. Click Done after finished.

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