Mac Not Mounting External Hard Drives? Fix it without Data Loss

If the external hard drive won't mount on Mac, you can download iBoysoft Data Recovery for Mac to safely and quickly recover lost data from unmountable external hard drives.

By Juno | Posted to Home > Mac Data Recovery Tips, updated on March 24th, 2021 |

Summary: External hard drive not mounting on Mac means that you can't access data stored on it. This page helps you mount external hard drives, as well as SD cards and USB flash drives, etc. on Mac. Besides, it also helps recover data from the unmounted external hard drives.

Usually, an external hard drive will appear (aka mounted) automatically on your Mac once you plug it in, and you can access data on this drive. So, it's annoying when you find that your external hard drive is not mounting for the com.apple.DiskManagement.disenter error or not recognized by your Mac, just like the user below.

"I have a 500 GB LaCie external hard drive, formatted as macOS Extend journaled on MacBook Pro 2014 and I have been using it to do Time Machine backups. Now after updating, macOS is not mounting this external hard drive. The main drive is greyed out in Disk Utility and the partition is not showing up. I can't do First Aid as my LaCie external drive does not mount on the MacBook Pro. Any ideas? Thanks!"

Wondering "why my external hard drives won't mount on Mac"? This post explains the reasons and teachs how to fix this disk problem without losing data.

Recover data from an external hard drive that won't mount?

As long as your external hard drive doesn't have any hardware problem, fortunately, you can retrieve your files with professional Mac data recovery software - iBoysoft Mac Data Recovery with no fuss.

Best External Hard Drive Data Recovery - iBoysoft Data Recovery for Mac

  • Recover lost data from unmountable, formatted, inaccessible, unreadable, corrupted external hard drives.
  • Supported storage devices: external hard drives, USB flash drives, memory cards, SD cards, etc.
  • Supported file types: photos, videos, audio files, documents, emails, etc.
  • Suppported Mac OS: macOS Big Sur 11/10.15/10.14/10.13/10.12 and Mac OS X 10.11/10.10/10.9/10.8/10.7.

Read-only & risk-free

Tutorial for external hard drive data recovery on Mac

  • 1. Free download and install iBoysoft Data Recovery for Mac on your computer, and then restart your Mac.
  • 2. Launch iBoysoft Data Recovery for Mac.
  • Recover lost data from not mounting external hard drive on Mac with iBoysoft Data Recovery for Mac
  • 3. Select the external hard drive that is not mounting and click Scan button to scan for all lost data.
  • 4. Preview the searching results, choose files you need, and click Recover to get them back.
  • Preview and Recover lost data from not mounting external hard drive on Mac with iBoysoft Data Recovery for Mac
  • 5. Have a check to ensure you have got all lost data back.

Note: You need to save the recovered files to another usable drive.

After having successfully restored all data on this drive, you can set out to erase this external hard drive to fix the disk not mounting on Mac issue.

Dos and Don'ts When External Hard Drive Not Mounting on Mac

Before you go further, it's better to know what you can do and can't do.

1. Do not go straight to reformat this not-mounted external hard drive unless you've restored data from it or backed up it before. Reformatting will wipe the data on this disk and cause serious data loss.

2. Do not run First Aid to directly repair the disk if you didn't restore data from it or back up it. Any further operation is very likely to overwrite your original files and make them unrecoverable.

3. Check if you have a copy of a data backup. If not, recover important files from this unmountable external hard drive first to avoid data loss.

Now, let's make the external disk accessible on Mac.

Fix external hard drive not mounting on Mac issue without data loss

Fix external hard drives not mounting issue on Mac

To access your external hard drive on Mac, try solutions suggested in this part one by one. Hopefully, you'll be able to open this external hard drive on Mac again.

First, try some simple tricks to mount external hard drive on Mac

In case you miss anything necessary, you can first have some basic checks as following:

1. Re-plug your external hard drive to another port or try another USB cable.

A faulty connection, though it is foolproof, might be the key fix if LaCie thunderbolt drive is not mounting, in that users always forget to check if the port is wobbly or if the cable is broken.

2. Try a super slow jam.

Strange but true, some users found that their external will mount properly when they plug it in exceptional slow motion. However, if they try and plug in the external hard drive normally, the Mac doesn't recognize the disk.

3. Check your Finder Preferences.

When your external hard drive does not appear on the desktop, you can open Finder, choose "Preference" (or press Command +, ) and check "External disks" both in General tab and in Sidebar tab to show your external hard drive on your Mac computer.

show mounted external hard drive on Mac desktop

If Mac could not mount the external hard drive on desktop still, let's troubleshoot this issue with the following solutions.

Solution 1: Force mount this external hard drive in Disk Utility

If you can't find the external hard drive on the desktop or in the Finder, you can try to make the disk online manually in Disk Utility (a native disk management tool in your Mac).

Here is how to mount an external hard drive on Mac:

  • 1. Click Go at the upper left of your desktop and go to Utilities, then launch Disk Utility on your Mac computer.
  • 2. Click on "Show All Devices" in View option to list or connected drives.
  • 3. Choose the grayed external hard drive in the left sidebar.
  • 4. Select Mount in the top center of Disk Utility.

However, if you find that your external hard drive is not showing up in Disk Utility (not a single volume but the whole disk disappears), it is very likely that your disk is suffering some physical damage. In this case, you need to send it to a local data recovery service. But if the Mount option is grayed out and you can see this external hard drive in Disk Utility, you can try another solution then.

Solution 2: Repair this unmountable external hard drive with First Aid

The second suggestion is First Aid in Disk Utility if you are unable to mount the external hard drive on Mac. First Aid is a very simple tool that is built in your Mac, and it is able to detect and repair directory damage and other disk errors. You are advised to run the tool more than once to ensure you are receiving a consistent result.

Note that you should recover data from the unmountable external hard drive if without a backup before running First Aid.

Follow the instructions and repair the external hard drive that is not accepted by your macOS or Mac OS X.

  • 1. Go to Utilities and launch Disk Utility on your Mac computer.
  • 2. Select the unmountable external hard drive on the left sidebar.
  • 3. Select First Aid in the top center and click Run.
  • Repair this unmountable external hard drive with First Aid

Solution 3: Reformat the unmounted external hard drive

If your external hard drive still can't be mounted in Disk Utility after you perform First Aid, or if First Aid failed to repair it like the situation below, your drive should have some serious errors like file system corruption.

Disk Utility failed to repair the not mounting external hard drive

Disk Utility can't repair this disk, what do to?

How to format external hard drives on Mac?

In this case, you need to back up your important data on the external hard drive, such as family photos, valuable work documents, or any other files. If you don't have a copy of a data backup in hand, the above guide can help you recover data from this unmountable external hard drive. And then, you can reformat your exteranl hard drive to make it work again on Mac.

Tutorial to reformat unmountable external hard drives on Mac

  • 1. Launch Disk Utility.
  • 2. Click the icon of your unmountable external hard drive on the left sidebar.
  • 3. Click on the Erase button function on the top of the Disk Utility window.
  • Repair this unmountable external hard drive with by reformatting
  • 4. Complete the related information (name, format, scheme), then click Erase button to finish reformatting.
  • Erase disk to fix unmountable external hard drive on Mac

After reformatting, your external hard drive will be assigned with a new file system so that you can mount this unmountable hard drive again.

Then, why we can't access the external hard drive on Mac?

Probably, the user above would never know why his MacBook is not mounting the external hard drive. As a matter of fact, this problem could be caused by many factors, such as damaged file system, virus attack, unsafe ejection or any other improper operations.

Here are some common ones.

  1. A damaged file system: If your external hard drive is attacked by virus or if you abruptly eject this drive, it's likely that the file system of this disk would be damaged or corrupted. As a result, the operating system is unable to recognize this disk, and the disk will not be mounted or read by macOS.
  2. Connection problems: Another reason that hard drive won't mount on Mac could be a dirty or loose connection between your cable, USB-C multi-adapter, Thunderbolt 3,  or other connecting ports. A clear, clean, snug and fit tightly connection is the premise of mounting an external hard drive successfully.
  3. Hardware issue: Also, problems related to hardware could also make the disk unmountable, especially when your external hard drive has too much bad sectors or have been physically damaged.

Knowledge Base: What does 'Mount' mean on Mac?

Mounting an external hard disk means the macOS gives a mount point (entrance) to read and access information on the hard drive. Information is accessed by the disk file system and partition table. So, it's a necessary step before the operating system can access a disk (including read from and write to).

Therefore, if an externalhard drive won't mount on Mac, it means the system gets into trouble in recognizing the file system or other information of this hard drive.

Conclusion:

If your external hard drive is not mounting on your Mac, don't panic. Most of the time, you are going to fix this disk problem with the solutions above. Moreover, if you worry about data loss when the disk becomes unmountable, you can use iBoysoft Data Recovery to recover your files first. Remember that, no matter what disk problem you meet, you should perform data recovery in case of losing data.