Usually, an external hard drive mounts automatically when you plug it into the Mac's port. And then you can find and access it on your Mac's desktop.
However, if you plug it in and nothing happens, it's likely not mounted. In such cases, the key isn't fixing it but diagnosing whether the drive has physical damage or is just not mounting like the user below.
"I have a 500 GB LaCie external drive, formatted as macOS Extend journaled on MacBook and I have been using it to do Time Machine backups. 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!"
Before we continue, bear in mind:
1. Do not go straight to reformatting this unmounted external drive unless you've restored data from it or backed it up before. Reformatting will wipe the data on this disk.
2. Do not run random tools. Any further operation is very likely to overwrite your original files and make them unrecoverable.
Now, let's troubleshoot the issue of the external hard drive not mounting on Mac.
Step 1: Does the Drive Appear in Disk Utility?
The first step is to check if your external drive shows up in Disk Utility.
Case A: Drive appears in Disk Utility and is mounted normally
→ The disk itself is fine.
→ If you still can't see it in Finder, likely causes: Finder preferences (external disks hidden)
The operating system has already completed the full chain: Hardware detected → file system recognized → volume mounted successfully
The drive is accessible to macOS, but Finder may not be displaying it because of Finder settings, sidebar settings, or a temporary UI issue.
Risk level: Low risk 🟢 (The drive itself is usually healthy. Data loss risk is minimal.)
Next steps: Check Finder settings
Case B: Drive appears in Disk Utility but is not mounted (often gray/dimmed)
→ The system detects the drive but can't access its file system properly. Possible causes:
- File system corruption
- Mount errors
- Directory/catalog damage
- Unsupported file system
- Minor partition issues
The hardware layer is working because macOS detects the device. However, the operating system cannot finish: Hardware detected → file system recognized → mount volume ❌
Risk level: Medium risk 🟡
The hardware may still be fine, but file system damage can become worse if many repair attempts are made.
Next steps: Mount in Disk Utility; Run First Aid, Recover data & reformat
Case C: Drive does not appear in Disk Utility at all
→ macOS isn't detecting the hardware itself. Possible causes:
- Bad cable
- USB hub issue
- Power issue
- Faulty enclosure
- Hardware failure
macOS fails at the earliest stage: Hardware detection ❌ The system cannot even see the device, so mounting and file-system checks never begin.
Risk level: High risk 🔴
Potential hardware failure. If the drive contains important data, avoid repeated plugging/unplugging or repair attempts.
Next steps:
- Try another cable
- Try another USB port
- Connect directly instead of through a hub
- Test on another computer
- Check System Information → USB
- If still invisible, consider data recovery or hardware replacement
Safe Recovery Order (Without Making Things Worse)
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 to another one to connect the drive to your Mac.
2. Plug in your drive very slowly.
Strange but true, some users found that their external drive would mount properly when they plugged it in at exceptional slow motion. However, if they try to 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:
- Finder > Applications > Utilities > Disk Utility.
- Click on the "Show All Devices" in the Disk Utility's View menu to show the external hard drive icon.
- Choose the grayed external drive in the Disk Utility's sidebar.
- 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), 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.
- Go to Utilities and open Disk Utility on your Mac computer.
- Select the unmountable external hard drive on the left sidebar.
- Select First Aid in the top center and click Run.
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.
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, read this, as it 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
- Open Disk Utility.
- Click the icon of your unmountable external hard drive on the left sidebar.
- Click on the Erase button at the top of the Disk Utility window.
- Complete the related information, including name, format(APFS/Mac OS Extended, and scheme, then click the Erase button to finish reformatting.
After reformatting, your external drive will be assigned a new file system so that you can mount this unmountable hard drive again.
If the Drive is NTFS (Windows-formatted)
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 Mac after upgrading 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 without losing data.
iBoysoft NTFS for Mac is professional NTFS for Mac software that supports macOS 26/15/14/13/12/11/10.15/10.14... It can mount NTFS-formatted external hard drives, USB flash drives, etc., with full read/write access without reformatting. Here's how to use it to fix the NTFS drive not mounting on macOS:
- Free download, install, and launch iBoysoft NTFS for Mac on your computer.
- Connect your Windows NTFS external hard disk to your Mac. Then, your NTFS drive will be mounted automatically. You'll now be able to open your NTFS drive and write to it.
Alternatively, you can back up the NTFS drive on a Windows computer and then reformat it with a Mac-compatible format.
When to Stop DIY and Consider Professional Help
You should stop trying DIY fixes and consider professional data recovery if you notice any of the following:
- The drive makes clicking, grinding, or repeating mechanical noises.
- The drive is not detected even in System Information (System Report).
- You experience repeated I/O (input/output) errors during access or repair attempts. (the com.apple.DiskManagement.disenter error, mount error 72, mount error 77)
At this point, repeated attempts may reduce recovery chances.
If Data Matters More Than the Drive
In some situations, the priority is no longer troubleshooting but recovering the data stored on it. You should consider data recovery if:
- The drive is to be reformatted, but its data is irreplaceable and not backed up elsewhere.
- The drive shows signs of progressive failure (e.g., intermittent detection, frequent disconnections).
- The system reports I/O errors or unreadable sectors.
- The drive is unstable but still occasionally accessible.
In these cases, continuing normal use or repeated repair attempts can increase the risk of permanent data loss. Use the professional data recovery software iBoysoft Data Recovery for Mac to recover the essential files.
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:
- Free download, install, and open iBoysoft Data Recovery for Mac on your Mac computer.
- Select the external drive that is not mounting and click the "Search for Lost Data" button to scan for all lost data.
- Preview the search results once the scanning is complete, choose the files you need, and click "Recover" to get them back.
- Ensure you have all lost data back on the not-mounted external disk.
Note: You need to save the recovered files to a different storage device. Also, data recovery is not guaranteed to succeed. It depends on the damage level:
- Minor logical corruption → high recovery success
- Severe file system damage → partial recovery likely
- Physical damage (clicking, head failure) → low or uncertain success
- Repeated failed access attempts → can significantly reduce the success rate
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.
Final Thoughts
If your external hard drive is not mounting on Mac, don't panic. If the drive still shows up in Disk Utility, you're in a much safer position. That usually means the hardware is fine and we're dealing with a file system or mounting issue, not a dead disk.
- If the external disk appears in Disk Utility, try manually mounting it.
- If manual mounting fails, try First Aid.
- If the disk is missing in Disk Utility, perform hardware checks.
- If the data is critical, recover it first.
- If the drive is expendable, reformat it.
FAQs about External Hard Drive Not Mounting on Mac
- QWhy is my external hard drive not mounting on Mac?
-
A
There are various causes of the external hard drive not mounting on Mac problem. It could be the connection issues or setting of the Finder preferences, and most likely, it is related to the damaged file system and hardware errors.
- QHow do you fix a hard drive that won't mount?
-
A
To fix an unmounted Mac external hard drive, you'd better recover data from it before you take any further steps. Then you can follow the 4 solutions we provide in this post to fix a hard drive that won't mount, including forcing mount the drive in Disk Utility, running First Aid to repair the drive, formatting the external hard drive, and using a third-party external drive mounter.
- QHow do I force my Mac to mount an external hard drive？
-
A
Using the macOS built-in Disk Utility, you can force mount a disk on Mac. Just select it from the sidebar of Disk Utility, and click on the Mount button to mount the selected external hard drive on your Mac.