Cannot mount external hard drive on Mac, how to fix?

Posted by Katrina to Mac Data Recovery on October 29th, 2018

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?

When you connect your external hard drive on Mac, if everything is working fine, the operating system will automatically recognize the device and mount its data in the Finder application. However, just like the above example, it may happen that the external hard drive is invisible on the left side menu of Finder and unmounted when checking in Disk Utility. Can't mount an external hard drive on Mac? This post will show you feasible solutions.

Mounting issues on Mac

There are numerous reasons for external drive not mounting issue, and below listed are few common ones:

  • >Connecting Hardware
  • >Corrupted disk
  • >Incorrect formatting of the disk
  • >Unsafe removal of the disk
  • >Sudden power disruption

Unable to mount external hard drive on Mac, how to fix?

The following are three effective solutions to external hard drives won't mount on Mac. But before running these steps, please do some basic checks.

Quick fixes of external hard drive not mounting on Mac:

1. Check whether the disk is properly connected to the system and powered on if required.

2. Try a different USB cable to make sure it is not at fault.

3. Try a different port/hub or plug another device in to see if the port/hub works. If you are sure that there is no problem with the USB port/hub, you can plug a working external drive in a port/on a hub, unmount and eject it. Then plug the unmountable external hard drive into that port/hub.

4. Check the file system of the external hard drive. Sometimes when the drive is formatted with NTFS, it can't be mounted on Mac. By default, macOS only enables NTFS drive read support but disables write support. In this case, you can mount external hard drive with the help of free NTFS driver for macOS.

Still unable to mount the external hard drive on Mac? There might be problems with the drive itself, but you still have ways to resolve it.

Back up at first

Since you can't access the external hard drive, all files stored on the drive are lost. In this situation, if you have important files on the external hard drive, any operation on the drive will overwrite the original data, resulting in irreparable data loss. So it's highly recommended to make a backup firstly. Forget to back up before? iBoysoft Mac Data Recovery can help you recover lost data from the unmountable external hard drive.

iBoysoft Mac Data Recovery is a free external hard drive data recovery tool that enables you to recover data from external drive which is unmounted, formatted, inaccessible, unreadable, or corrupted. It's fully compatible with macOS Catalina 10.15/Mojave 10.14/High Sierra 10.13/10.12 and Mac OS X 10.11/10.10/10.9/10.8/10.7. It supports data recovery from hard drive, external hard drive, USB flash drive, SD card, memory card, pen drive, etc.

Tutorial to recover data from unmountable external drive on Mac with iBoysoft Mac Data Recovery

Step 1: Download and install iBoysoft Mac Data Recovery on Mac.

Step 2: Launch iBoysoft Mac Data Recovery.

Recover data from unmountable external hard drive on Mac

Step 3: Select the unmountable external drive drive and click "Next" button to scan all lost data.

Step 4: Preview the searching results, choose files we need, and click "Recover" to get them back.

Step 5: Have a check to ensure we have got all lost data back.

Solution 1: Repair the external hard drive with Disk Utility

Step 1: Launch Disk Utility.

Step 2: Choose the unmountable external drive on the left sidebar.

Step 3: Select First Aid in the top center and click Run.

First Aid

Solution 2: Repair the external hard drive with Terminal

Sometimes, Disk Utility may not function as desired. But you can still repair the corrupted external hard drive with Terminal.

Step 1: Go to Applications > Terminal

Step 2: Enter: diskutil list (This will list out the available volumes).

Step 3: Check the volume identifier from the table that appears.

Step 4: Enter: diskutil repairVolume [diskvolume identifier]. For example, if the volume identifier of external hard drive is disk2s, you should enter diskutil repairVolume disk2s.

Solution 3: Reformat the external hard drive

If your external hard drive can't be repaired with Disk Utility and Terminal, the drive might be seriously corrupted. The only way is to reformat it. Reformatting will erase all data on the external hard drive, please make sure you have backed up important data.

1. Launch Disk Utility from Utilities.

2. Click the icon of the unmountable external drive on the left part of the window.

3. Click the Erase function on the top of the Disk Utility window.

Erase external hard drive

4. Complete the related information (name, format, scheme), then click Erase button.

Still have questions?