External Hard Drive Not Mounting Mac? Fix It without Data Loss

Usually, an external hard drive will mount automatically once you plug it into the Mac's port. And then you can find and access the external hard drive on your Mac. So, it's annoying when you find that your Mac external hard drive not mounting for the com.apple.DiskManagement.disenter error, failed with 72 error, failed with 77 error, or not recognized by your Mac, just like the user below.

"I have a 500 GB LaCie external 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 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 drive won't mount on Mac"? This post explains the reasons and teaches how to fix this disk problem without losing data.

Quick takeaways for external hard drive not mounting on Mac:

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First step: Recover data from an external hard drive that won't mount

Couldn't mount my external disk. Restarted, tried (even) my Catalina partition and nothing. 

Downloaded iBoysoft just to try to double check if any essentials are on there. 

Then after 5 hours it's mounted. HOW? Is it on it's last legs?
WHAT?

— Steve Curtis (@stevenpcurtis) November 24, 2020 

Tutorial for external hard drive data recovery on Mac

After having successfully restored all data on this drive, you can set out to erase this external drive to fix the external hard drive 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 and can't do.

 1. Do not go straight to reformat this not-mounted external 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 drive first to avoid data loss.

Now, let's troubleshoot the issue that external hard drive not mounting on Mac.

Fix the external hard drive not mounting on Mac

To mount an external hard drive that is not mounting on Mac, try the solutions suggested in this part one by one. Hopefully, you'll be able to open this external drive on Mac again.

Solution 1: Simple tricks to mount an external hard drive on Mac

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

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

A faulty connection, though it is foolproof, might be the key fix if the LaCie thunderbolt drive is not mounting, in that users always forget to check if the Mac's USB port is wobbly or if the USB cable is broken. If you are using a USB connector or adaptor, change another one to connect the drive with your Mac.

 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 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 "Settings" and check "External disks" both in the General tab and in the Sidebar tab to show your external hard drive on your Mac computer.

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

Solution 2: Force mount this external hard drive in Disk Utility

Sometimes, your external hard drive is not recognized after the force ejection from your Mac. If you can't find the external drive on the desktop or in the Finder, Disk Utility is the last place you can find it. Some Mac users reported that the external hard drive shows up in Disk Utility but won't mount. In this case, you can force-mount the disk on the Mac.

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

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), your disk is likely 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 3: Repair this unmountable external hard drive with First Aid

The second suggestion is First Aid in Disk Utility if the external hard drive not mounting on Mac. It is a very simple tool that is built into your Mac, and it can 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 drive without a backup before running First Aid.

Follow the instructions and repair the Mac external hard drive not mounting.

Solution 4: 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 Disk Utility can't repair this disk, your drive should have some serious errors like file system corruption.

How to Format an External Hard Drive on Mac?

Read this detailed guide to format your external hard drive on Mac. You can format the external hard drive for PC and/or Mac.

In this case, you need to back up your important data on the external drive, such as family photos, valuable work documents, or any other files given that erasing the drive will delete all the data. 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. Then, you can reformat it to fix external hard drive that is not mounting on Mac.

Tutorial to reformat unmountable external hard drives on Mac

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

Solution 5: Use a third-party external drive mounter

When you format the drive with an macOS unsupported file system on a Windows PC, you will fail to mount it on Mac. If you find your NTFS drive won't mount on macOS 10.15.7 after the Apple security update on March 17, 2022, and the "com.apple.DiskManagement.disenter error 49221" issue occurs when you're trying to mount it with Disk Utility, then, the solution is a little different from the above. Instead, you should use professional NTFS software to fix it.

iBoysoft NTFS for Mac is a professional NTFS for Mac software that supports macOS 15/14/13/12/11/10.15/10.14... It can mount NTFS-formatted external hard drives, USB flash drives, etc. with full access. Here's how to use it to fix the NTFS drive not mounting on macOS:

Have you already fixed that the external hard drive not mount on Mac? Please share this article to help more. 

Why can't mount 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 systems, virus attacks, unsafe ejection, or any other improper operations.

Here are some common ones.

Why not share this article if you know how to fix the external hard drive not mounting on Mac?

Conclusion

If your external hard drive is not mounting on 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 for Mac to recover your files first. Remember that, no matter what disk problem you meet, you should perform data recovery in case of losing data.