Big Sur - external discs not mounting

Fixed my Samsung T3 SSD connection like this:
open disc utility
select the drive in left side of window (mine showed in a different section below other discs that were working).
click the “first aid” icon at top of window
choose “Run” in the pop up window.
mine ran and fixed, now visible in finder, all files in tact.

…except that once I ejected it, it would not mount again from the same USB port…. Mounted fine from a different port. Hoping just a ‘time since dismounted’ issue.

I too am having the same issue. Have tried all of the suggestions above but with no luck. Have a fair bit of music on there that I want to transfer over to another drive. Stopped mounting just after I put the files on there and wanted to back them up elsewhere for a second copy as they were recovered from a damaged drive. Drive worked fine for a while but then nothing.

I can see the drive in disk utility but it won't mount at all. Have also tried other drives and the same is happening. Thought it might improve after the latest update to 11.3, but I guess not.

I was having this problem in Big Sur as well. 2 of my 3 external drives would not show up on the desktop or in disk utility. If I booted in Catalina they all showed up. What fixed it for me was swapping out a USB cable. I was using a long (10ft) cable and I replaced it with a 2ft cable and now all the drives show in Big Sur. It seems, in my case, the Big Sur didn't like the long cable...

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 to 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. I used a different computer to do this.

I found some suggestions on the LaCie support site.

Some Seagate and LaCie software use a kernel extension (kext). Apple
silicon Macs require that users change the security settings to ‘Reduced
Security’ for the software to function properly.
To change the level of security on your startup disk:

Shut down the Mac
Press and hold the power button until you see “Loading startup options”
Click Options
Click Continue
If asked, select a user > Click Next > Enter password for admin account

In the menu bar at the top, Select Utilities > Startup Security Utility
Select the startup disk
If the disk is encrypted, Click Unlock > Enter Password > Click Unlock

Click Security Policy
Select Reduced Security
Put a check next to “Allow user management of kernel extensions from identified developers”
Click OK
Enter admin password > click OK
Once changes are applied, click the Apple icon and Restart

I'm in the same boat as as others since finally upgrading to Big Sur 11.3.1 on my MBP11,2 and can't get any of my external NTFS drives to be mounted on my MBP.

IMHO... The worst thing to do is to format the drive "willynilly" without backing up all the contents. I'm a DJ and have over 2GB of songs that I am not just going to format and delete forever. The second worst thing to do is follow the above the above post as they must have a Hackintosh because their comments makes zero sense.

I tried using my long time trusty app Mounty.app (v1.12) to mount my NTFS drives on Big Sur (worked amazingly on Catalina) but now I get an error "Volume "XXXX" not demountable. The volume is not re-mountable in read/write mode. Probably it was was not clean unmounted before."

The best option I found is to back up the NTFS extrenal HD on a Windows OS 7-10 computer (if you can find one), then format the drive as exFAT on your Mac, then reinstall the files from the Windows computer back onto the external exFAT HD.

The answer that worked for me is what drmwho noted above:

<quote>
I found some suggestions on the LaCie support site.

Some Seagate and LaCie software use a kernel extension (kext). Apple 
silicon Macs require that users change the security settings to ‘Reduced
Security’ for the software to function properly.
To change the level of security on your startup disk:

Shut down the Mac
Press and hold the power button until you see “Loading startup options”
Click Options
Click Continue
If asked, select a user > Click Next > Enter password for admin account

In the menu bar at the top, Select Utilities > Startup Security Utility
Select the startup disk
If the disk is encrypted, Click Unlock > Enter Password > Click Unlock

Click Security Policy
Select Reduced Security
Put a check next to “Allow user management of kernel extensions from identified developers”
Click OK
Enter admin password > click OK
Once changes are applied, click the Apple icon and Restart

• ***********

Once you adjust startup security, restart and reconnect the drive, it should work. It has to do with letting the drive's software install a kext so it can mount, as I understand it.

Good Luck! I struggled and cursed Apple's lack of info on this, finally succeeded.

I also found Glenn Fleishman's "Take Control of Your M-Series Mac" very helpful, although he does not specifically address this as a fix for hard drives not mounting. His section on the startup security settings gave me confidence that this was a real, safe thing to do (not just a drive manufacturer hack). Lots of other great M1 info also.

Once I did this, the drive mounted and showed up in Disk Utility, which it would not do before. Hooray!

Same problem with external HDD not recognized on my new MBP M1 macOS Big Sur 11.3.1.

• 4 and 14TB Toshiba 3.5" drives purchased in January, formatted Mac OS Extended(Journaled), and files saved on my Mac Pro 2012 macOS Sierra 10.12.6

• these drives not recognized on my MBP file manager, Disk Utility, or Chronosync app

• tried on a new Terramaster D5 Thunderbolt enclosure, also on a new Insignia 2 bay HDD station

• reset MBP permissions to reduced security (as described above), restarted and same issues, no drives visible on file manager, disk utility, or Chronosync.

• reinstalled drives in my Mac Pro and they are recognized and work normally.

Any ideas to fix? My MBP is worthless to me if I can't read my media files

Hi all! I was having the same issue and discovered that there is a known bug that was introduced with macOS 11.2 for the SoftRAID app. This bug prevented the driver from loading on M1 Macs. The fix is actually simple and relatively painless.

If you've got macOS 11.2, upgrade to 11.3 or later (current latest is 11.4) and download SoftRAID 6 from from https://www.softraid.com/. It was free update for me as my OWC drive came with SoftRAID 5, but otherwise it costs $$.

I've been battling with the same thing with a 1TB SanDisk Extreme SSD. I did some experimenting and this is what I've found (I'm on a M1 MacBook Pro btw)...

If I go USB C > USB C (either using the Apple cable that comes with the charger or 3rd party) then I get the kind of issues that others are reporting here. I'm pretty certain it never caused me an issue till after updating to 11.2 or 3, but anyway.

If I plug in a USB C breakout cable to my Mac - the kind that gives you multiple USB A, HDMI, Micro SD ports etc, plug the drive into that going USB C > USB A. It works just like it always did.

Not sure why it makes any difference, but in my case it does.

Hey Everyone,

So I may have figured out a fix for external hard drives not mounting at least to a MacBook pro. I noticed my hard drive wasn't mounting with my laptop after I didn't press the unmount button before removing the cable. It has worked still with PC's though. To get my MacBook pro to work again, I had to create a new Apple profile for my MacBook. I noticed the external would work on the new profile but not on my original admin profile. But after it mounted on the new profile, I logged out and logged back into my admin account and sure enough, it started mounting again like new. Worth a try right? I have updated to the most current Sur version by the way.

so for me i had to update my external hard drive and the software that comes with it!

Any update on this issue? If you do answer, please do not ask about formatting of the external drive, or possible bad usb cable. I plug in 4 different external drives that all worked prior to updating to Big Sur, now they don't. Has Apple provided a fix for what is obviously a bug in their Big Sur update?

I faced the same issue after upgrading my Mac to Mac OS Big Sur. I was able to mount the external HD, after running First Aid from Disk Utility. The content of the drive was preserved as well. Hope this helps.

I've had the same issue but I haven't upgraded to Big Sur yet - I'm on Catalina and 10.15.7 IOS with 2019 Macbook Pro that I bought new last December. I have a few external hard drives - 2 Seagates and a WD - the WD is partitioned for Time Machine and the other partition is for files I drag on it for easy access.

One Seagate has movies and media on it while the other has mostly documents. I've done the disk utility thing - Was able to mount the WD but not the Time Machine side - which is frustrating - it's. 5TB drive! It can be read on my ****** PC and my old MacBook mid-2012 that is using High Sierra but not on my nearly brand MacBook pro. I feel like I need to go and buy another hard drive just to back up my newer Macbook - to be safe while the rest gets sorted out. I'm concerned about my computer backup on Time Machine - anyone else have this issue?

I do not want to erase my other hard drives - The WD is pretty new too - only bought it a few months ago - I agree with everyone how frustrated I am with Apple - and though I'm pretty tech-savvy, I may just say the hell with it and go to the Genius bar to have them figure it out. I've wasted hours upon hours (days even) on this - time I don't have to spare. Funny how the drives can be seen on a ****** lenova pc but not on my expensive macbook pro. It seems crazy to have to create a new profile or erase perfectly good hard drives - this problem is with Apple, not the hard drives, or else I wouldn't be able to see them on my old Mac and my ****** PC.