10.15.7 update made my external drives unmountable, Diskmanagement Dissenter Error

[AirBear]

Posted this as a reply on a week old thread but thought it deserved it's own post:

When my 2020 iMac upgraded to OS 10.15.7 I lost the ability to mount all my external devices. I had a 4TB FireCuda (Thunderbolt3) and a 256GB MicroSD card. As a test I plugged in a 3TB USB3 Seagate drive. Same error message when trying to mount "Could not mount "(diskname)", (com.apple.DiskManagement.disenter.error xxxxxxxxxx. The error number varied by which drive it was.

The SD card and USB drive I was able to plug into my wife's 2012 Mac Mini, and I got the same error message. So something was done to the drives. At least on her computer I was able to erase and reformat and afterwards they showed up fine on the iMac. But the Firecuda is TB3 and the Mini only has TB2 and I don't want to have to buy a $50 adapter.

Yesterday morning I spent over an hour on the phone with Apple tech support. Got elevated to senior tech support, then to the engineers. Expecting a call back later today. As of now they want me to do a clean install of Mac OS and even make a different user account. Not worth reinstalling all those apps. I used M3 data recovery and after 18 hours it was able to show me the directory structure on the Firecuda but the free version is capped at 1GB recovery, which I used for some .epub files. Full version is $100, again not worth it.

Today I booted my iMac from the old Mac Mini 500GB drive which I had replaced and had sitting in the closet. It has Catalina 10.15.3 still on it. Still got the same error message when trying to mount the Firecuda. The other 2 I had reformatted on the Mini and again they now work fine. So 10.15.7 did something to the external drives where even another Mac can't mount them. I'll probably wind up erasing the Firecuda rather than paying $100 or doing a clean install of Catalina. Senior Tech advisor said they've only seen a few cases of this happening.

I have one more trick up my sleeve, I know from doing volunteer work refurbishing old computers that Ubuntu Linux runs well on a Mac, had to use it when I didn't have the ability to reinstall Mac OS on a wiped hard drive. I can boot Ubuntu into RAM and possibly copy my files over to the 3TB USB drive.

 

[AirBear]

Ubuntu Linux helped me solve this. I booted from a flash drive and loaded Ubuntu into RAM. I was able to access the Firecuda drive with no problem in the Linux OS. I could not get files to xfer between external drives, so I uploaded to a Google Drive. Then I formatted the Firecuda with Linux. Rebooted into Mac OS 10.15.7 and was still unable to mount the drive. So I booted into 10.15.3 using the Mac Mini's old hard drive in a USB enclosure. Then I was able to format the Firecuda. After rebooting back into .7 I could now mount the Firecuda and start transferring files from Google Drive.

I've been working with Brad at Apple's Senior Tech Support. They didn't have a solution, had suggested the clean install I mentioned above but they forgot the drives had the same issue on my 2012 Mac Mini. LOL, he was impressed with my solution and asked for detailed info on how I did it.

 

[chscag]

Thanks for posting the solution. We did remove your dupe reply that you posted to another thread. Always better to start a new thread.

Been a awhile since I used and played around with Ubuntu. Good to know that it was useful in solving your problem.

 

[Rod]

How was the Firecuda formatted originally? Was it originally erased and formatted as Mac OS Extended (Journalled) by you before use?
The reason I ask is because I still suspect there was some proprietary software on it causing the problem which fits perfectly with your solution and why Ubuntu was able to mount it.

 

[AirBear]

How was the Firecuda formatted originally? Was it originally erased and formatted as Mac OS Extended (Journalled) by you before use?
The reason I ask is because I still suspect there was some proprietary software on it causing the problem which fits perfectly with your solution and why Ubuntu was able to mount it.

I think it was Mac OS Extended. 1st thing I did when this happened was to uninstall Paragon's NTFS for Mac. I was warned on this forum a long time ago apps that dig deep into the OS can cause issues. When I reformatted I did Extended Journaled.
Again, it was the same issue with a 256GB MicroSD card, a 3TB USB3 external, and the Firecuda. I dug the 3TB out of the closet just as a test. Anything I plugged into 10.15.7 was affected.

 

[Rod]

Thank you so much for getting back on this. I guess that rules out the devices. The next thing I would do is search to see if others have had the same issue with the same Catalina update. I'll have a browse later today.

 

[Rod]

Well it seems you are not alone. 645 posts in Apple Community from 2019 up to the present day; https://discussions.apple.com/thread/250742324?page=1
It seems users have been having this issue since the release of Catalina. Lots of solutions have been discussed, some worked, some did not. There does not seem to be a "one size fits all" solution, nor, obviously, is this a universal problem.
The question is always the same, what's different?