Unable to access External Drives and Disk Utility after updating to macOS Sonoma.

For me on M1 PRO MBP the issue looks like Sonoma is somehow reliably corrupting external exFat SSDs on every shutdown. If I unmount my SSDs before shutting down, they mount and work flawlessly on next start. But when I shutt down with the external SSD mounted, then it becomes unusable. To solve this state I... connect the drive to a Windows PC. It works but offers to scan and repair the drive as it detected errors. After the short repair procedure under Windows magic happens! It works again under Sonoma again! Until ofcourse I forget to unmount before the shuttown and let it mess with my drive again. I've lost so much time and some data on this issue. It is absolutely unacceptable and infuriating to release update like this... But if it's by design that is disgustingily outrages eneough for me to ditch the entire Apple ecosystem whatsoever. It doesn't seem to be the software up to any proffesional standards.

I had the same problem.

I have seen prompt that just blink. I made screenshot and it's say "Allow accessory to connect?" and it was disappeared very quickly.

After Googling, I found solution for me.

Going to Settings->Privacy & Security->Scroll Down->Allow accessories to connect->Set to Automatically When Unlocked.

So, I connected SSD and it works well. After that I switch settings to "Ask for New Accessories" as was before.

I think it's bug in MacOS because disk or MacOS doesn't waiting answer from the user

I hope it helps for somebody

I have been having this issue with my two Western Digital external HDDs (exFAT formatted) since I upgraded my MacBook Air M1 to Sonoma, but I could find two workarounds and one fix (not ideal, but seems to be working). As this laptop suffers from scarce USB-C ports, I have been connecting these drives via a Baseus 6-in-One USB hub.

I recommend you who still can't access your external drives to try one of these and see how they work for you.

It seems that MacOS actually had unknown issues mounting the drives. The system does acknowledge there's a drive inserted in one of its USB ports, but isn't mounting the drives immediately as it should.

Workaround #1: case you have a Windows machine laying around, plug your device to it. Windows will give an alert saying 'the unity is damaged. Do you want to repair it?'. Accept the scan. It can take some time, depending on your drive size. My 2TB unit takes around 10 minutes. My 5TB one takes around 30. Can be still faster than workaround #2, depending on your drive size

Workaround #2: for whatever the reason, as soon as MacOS gives up mounting the drive, it begins a scanning proccess running in the background (which you can watch by typing 'ps aux | grep fsck' at the Terminal). My Terminal gives me two lines as the answer, and one of them ends with '/dev/rdisk4s1' (rdisk4s1 is probably the drive id, yours can be different) - that line contains the exact time count of that scanning proccess.

When this background scan finishes, the drive will mount. It might take a lot of time. My 5TB drive takes almost one hour until it mounts. But in the end it will and you can use your drive as usual.

Both these workarounds aren't practical if you work with your Mac. But feel free to try. If they worked for me, chances are they'll work for you too.

Now, the fix. This one did it for me for good:

• Apple Icon > System Settings. At 'Privacy & Security' tab, look for 'Allow Accessories to Connect'. Set it to 'Automatically when unlocked'. Try connecting the drive again. Should work.

Good luck!

And please, Apple, solve this next update! This is just too frustrating.

Using an active USB hub did the trick for me.

I purchased a TP-Link UH720 USB 3.0 hub which is an active hub, meaning you have to plug it into the power socket too. Then I used a USB 3.0 to USB-C adapter cable and it works. macOS sees all my external SSD drives just as before the Sonoma update.

Nonetheless, this is still infuriating from Apple.

I had the same problem, but I found a solution. Using the Disk Manager in Windows, I reformatted the disk with ExFAT filesystem, but with Allocation Unit Size set to 128k (don't choose Default, which is 1024K in Windows). After that, the disk will mount in Sonoma (I'm running 14.1).

See: https://iboysoft.com/questions/is-there-any-way-to-fix-an-exfat-drive-not-mounted-on-mac.html

I have an external Western myBook Duo (4TB + 4TB) in RAID 1 configuration (USB3.+), formatted exFAT because I have cause to use it with both Mac & Windows. It frequently fails to mount on Mac, and Disk Utility can't repair it. I can still mount it on my Windows system, at which point I can use the Windows Explorer>Properties>Tools>Error Checking, where it always indicates a disk error. Windows then repairs the drive, after which the drive will once again mount on the Mac. I had this same issue with a previous Mac OS (one of the later 10's), but eventually it seemed to have been resolved--until I updated to Sonoma.

My system updated to Sonoma 14.3.1 on 2-9-24, it still causes failure of the Thunderbolt/USB-4 ports to function properly. The ports worked perfectly with Ventura OS. This is my second attempt to upgrade to Sonoma on my 2023 Mac Mini M2 8G with 250G with Ventura installed. This time, in addition to my 2-T NVM drive disappearing, my USB-C connection to my monitor failed. In other words, both of my Thunderbolt/USB-4 ports would not work correctly. I spent a few hours with Apple support on this issue and it became apparent that they didn't have a clue what was wrong. Documented and recorded the malfunctions and sent to Apple engineering for escalated assistance, expecting a call back on 2/13. Not holding my breath, I canceled Sonoma, wiped my internal drive and clean installed Ventura 13.4 then restored files and settings with Time Machine. Both ports are now working perfectly!

FIX FOUND! I wondered if the issue was power to the ext drive. ( OWC Elite Pro ) I have an iMac M1 2021 with 4 USB sockets. Since I had my keyboard plugged into socket 1 ( looking from the back left to right ) I had been plugging the drive into socket 3 as I have another device into socket 2. I disconnected the keyboard and plugged the drive into socket1. VOILA! the drive showed up on my desktop and in Disk Utility. As an experiment I plugged the device ( an integrated amplifier ) that had been in socket 2 into socket 4 and it no longer showed up on my computer as it had before! I tried to find information about the power to the ports but didn't find anything useful in a cursory look. Hope this helps.

Hi All,

I just fixed my "external SSD not mounting after upgrade to Sonoma" issue.

I called Apple Support and they walked me through EVERYTHING else that I found here and on other forums, as well as things I knew to try myself. I, myself, am a level 3 support tech, and didn't think of the last TWO things the tech, Dustin, had me try and it fixed the problem.

ITEM 1

1. shut down (not restart)
2. boot into Restore mode

• • as soon as you hear the machine ding indicating it is starting up, press and hold Command+R
  • Hold until apple appears (only 1-3 seconds on my machine)
  • once in restore mode, I already saw the drive blinking indicating it was working

ITEM 2

1. System Settings --> General --> Login Items
2. In the "Open at Login" dialogue box at the top, if there is ANYTHING in there, remove it

• • Sonoma may be finicky on your machine
  • If it is, it will NOT boot the drives FIRST if it sees anything in that dialogue box
  • Instead, it will stop the boot sequence and ensure that those startup items are running
  • And it therefore may not come back around to your drive

These totally did the trick for me. Hope it works for you.

Happy New Year All

I have a pretty much state of the art 2023 Mac Mini M2 8G ram, 256 internal, and a 2T external SSD FORMATTED in APFS since day 1. The computer came with Ventura installed and the SSD worked perfect! Then I recently migrated to Sonoma 14.2.1 and the external ssd drive disappeared after rebooting, never to be seen again by Sonoma. WTF?  

I tried all the tricks and still no external ssd to be found. 

It is an outrage that the recent update Sonoma 14.3 does not correct this critical flaw!

Out of frustration, I concluded that Sonoma sucks and I restored Ventura as follows:

On a Mac with Apple silicon your computer must be connected to the internet. If you’re reinstalling on a Mac laptop, plug in the power adapter.

1. Shut Down your Mac, press and hold the power button until “Loading startup options” appears, select Options, click Continue, then use Disk Utility in the Recovery Window to initialize your drive APFS, which wipes it clean.
2. Then, In the Recovery app window, select Reinstall for your macOS release, click Continue, then follow the onscreen instructions. 

After I reinstalled Ventura, I restored the most recent Time Machine backup, which was only 2 days old. Being very grateful that all my precious data had not been chewed up and destroyed by Sonoma as some have reported happened to their external drives data. Did I mention that my Time Machine is on the external SSD?

I’m happy to be back with Ventura. For me, there is absolutely nothing compelling about Sonoma that warrants having to put up with any hassles with it. 

Update: I found a fix that worked for me on another thread. Someone talked to an apple engineer who suggested using a USB to USB-C adapter. I was highly skeptical but having tried everything and having some adaptors on hand I gave it a try and it worked!

so on a M3Pro I plugged in a USB-C to USB adapter and then plugged a USB to USB-C adapter into the first adapter and then my SSD into the second adapter and it now mounts.

Ridiculous 😂 have no idea why this would work but hey at least it’s working.

Apple needs to prioritize a proper fix to this as this is unacceptable to have a such a serious bug be going on for 6 months now.

Hey there! One of my coworkers is also having the same issue with her external G-Tech Raid. When mounted to her previous system running Big Sur she sees all files on the drive. When mounted on her system that has been updated to Sonoma she is missing more recent folders and files. We have tried multiple things to get it to work. But clearly, its an OS issue because everything was working on her new system prior to updating to Sonoma. The drive is also formatted in EX-FAT. Looks like the only option is to downgrade the OS

DaniMS wrote:

totally. Spent 2 hours yesterday with Apple support and was useful. I just realized that can mount the disks through disk utility in safe mode but can't in normal one. Apple asked me to reset from factory settings my mac but don't wanna do it because it'll be a nightmare to get everything back.

That would imply you may have a third-party system modification installed that is causing the problem. You wouldn’t need to reset it, but just uninstall the system modification. The only drive-related modifications I’m aware of are the NTFS drivers that come bundled on drives. It is well-documented here that they will prevent mounting of drives.

Try leaving your drive with the EFAT partition connected to the computer for about 15-30 minutes. without performing any operations. Observe the behavior of the disk. The disk then carries out the mounting process, which in the case of the Sonoma system takes an absurdly long time. I have a 16 TB WD external drive, it takes almost 30 minutes and only after that time it is mounted and visible in the system. During this time, the Disc Utility system program hangs if I run it. In other words, plug in the disk and do nothing, wait.

Yep this is happening on my M1 mac pro which is running Sonoma. It loads the external harddrive and then removes it. Doesn’t even unmount so it gives itself the warning of unplugging devices without unmounting it first. Anyways logged in through Safemode and had no issues being able to see and access the external drive. Note its a WD box with a straight usb-c interface. Ran the disk utility and even reformatted it to be apple files system to be sure. Nope still forcefully ejects the drive if it’s plugged in before log in and doesn’t see it if I try to plug it in. But safe mode has no issues detecting and loading ext hd.