External Drives not recognised in Tahoe

[Ifti]

Strange - I have tons of external SSD drives - both RAID (using SoftRAID) and single drives, exFAT, HFS+ and APFS, across USB4, Thunderbolt 3, 4 and 5 interfaces. All work perfectly fine on a Mac Studio M4 Max.
Upgraded to Tahoe from Sonoma a few weeks back and been using them as normal.
Wonder if it is more isolated to Intel based machines.....
Is your MacBook an Apple Silicon machine? If so you could always try upgrading that to Tahoe and see if they work.....although downgrade the iMAC first so you can still access the drives somewhere at least!

 

[Skoobunny]

Strange - I have tons of external SSD drives - both RAID (using SoftRAID) and single drives, exFAT, HFS+ and APFS, across USB4, Thunderbolt 3, 4 and 5 interfaces. All work perfectly fine on a Mac Studio M4 Max.
Upgraded to Tahoe from Sonoma a few weeks back and been using them as normal.
Wonder if it is more isolated to Intel based machines.....
Is your MacBook an Apple Silicon machine? If so you could always try upgrading that to Tahoe and see if they work.....although downgrade the iMAC first so you can still access the drives somewhere at least!

The situation is even more interesting. My wife's MacBook Air M3 has no problems after switching from Mac OS Sequoia to Mac OS Tahoe. My MacBook Pro M3 (Pro) cannot work with external drives after upgrade.

 

[Fishrrman]

OP:

Unless there is a specific, absolute reason why you NEED "case sensitive", DON'T use that option.

I prefer HFS+ for ALL my drives, unless they MUST be in APFS.
"Mac OS extended, journaling enabled, case INsensitive, GUID partition format"

 

[davidjames1701]

hi, sorry for they delay, busy week,
!. I'm using erase from disk utility and selecting APFS as the GUID portion Map, if that's what you mean?
2. its a Sandisk SSD, 1TB, connected directly to a std USB port, I've tried that drive in all four std USB ports.
3. is this ok ?

 

[davidjames1701]

 

[davidjames1701]

Ok, thanks Lou, ill try a hub

tried a hub, no joy, still the same I'm afraid

 

[davidjames1701]

1. Do they mount another user account?
2. Can you run First Aid on them while unmounted?
3. Have you tried mounting in terminal? If not, the errors message may help identify the problem.
4. Have you tried rebooting in Safe Mode? If they mount there, you might have some incompatible software installed.

To mount in Terminal, enter “diskutil list” and press Return. Identify your drive by size, name, or type (e.g., /dev/disk2 for an external HDD; note the volume identifier like /dev/disk2s1). Then type “diskutil mount /dev/diskXsY” (replace with your identifier, e.g., diskutil mount /dev/disk2s1) and press Return.

If they do mount after this, I’d run First Aid on them again.

Hi, haven't tried them on another account on same machine, but ran First Aid in Disk Utility ok -

 

[bzgnyc2]

hi, sorry for they delay, busy week,
!. I'm using erase from disk utility and selecting APFS as the GUID portion Map, if that's what you mean?

Yes

2. its a Sandisk SSD, 1TB, connected directly to a std USB port, I've tried that drive in all four std USB ports.

From the Disk Utility screenshot I can see this is a SanDisk Extreme SSD though it's not enough to distinguish between their 3 versions of this product: SDSSDE60, SDSSDE61, SDSSDE62. These appear to have very difference performance and therefore one can assume different internal electronics. Knowing which model may be helpful for troubleshooting.

I also note firmware updates available for some models fix severe issues under Windows 11. It's possible that the same bugs now also break this drive under Tahoe. You might try updating the firmware just to see...granted that means finding/making a Windows system to run the updater on the drive.

Also I notice this is a native USB-C drive and assume you are using the included USB-C to USB-A cable. Can you try using a USB-C <-> USB-C cable plugged straight into the Thunderbolt 3 port (which will then drop down to USB 3 but at the same time avoid the adapter cable). This shouldn't make a difference but then again you shouldn't have this problem...

3. is this ok ? View attachment 2568455

This is part of it but already interesting. It's only the showing the internal drive here despite Disk Utility showing an APFS container and volume. And also successfully running First Aid on the filesystem. So the OS can see and access the drive. The kernel filesystem driver just can't see it.

Can you post a snapshot or copy/paste of Info from Disk Utility? (upper right-hand corner in Disk Utility)

Also the USB section of System Report? Just to make sure there's no unusual connection there.

Finally, if you can use Terminal, the output of "diskutil info disk4" (assuming "disk4" is what appeared as the "BSD device" in the output of Info from Disk Utility)

Note that this could just be a macOS system bug (e.g. the FB13749402 mentioned above if ChatGPT didn't hallucinate) in which case you might just have to wait for a future version of macOS to use this drive under Tahoe.

 

[gilby101]

It's only the showing the internal drive here despite Disk Utility showing an APFS container and volume.

I think that is because system Information > Storage only shows mounted volumes.

There is something odd here with the macOS volumes. I expect "Macintosh volumes" and "Macintosh snapshot" to be in bold text. Only "Macintosh" should be grey. This doesn't directly relate to issue with external drives, but may indicate an underlying problem.

It would be really good to see Terminal output. Open the Terminal app. Type diskutil list and show us all the output.

 

[gilby101]

ChatGPT said so

Can you provide some more detail on FB13749402? Not just ChatGPT output. When I do a web search, I can find no other reference to this bug number.

 

[McScooby]

Haven't updated to Tahoe yet, but see no-ones mentioned the obvious (esp if they're shown in Disk Utility) - Finder, Settings, General and ensure that hard drive visibility on the desktop is checked?

IIRC, think there was a previous similar update that removed it, so may be the same with Tahoe

 

[caver]

Thanks for sort of leading me in the right direction.... Was troubleshooting this too..... When you mentioned ESET I knew that couldn't be a coincidence. Here's where I learned that device control blocks usb drives by default. Either turn the feature off (which will have it always telling you that it's off and being annoying) or turn the blocking off (by using the menu bar to click on the eset app name (in my case eset endpoint security) > Settings > Device control > rules remove the check mark from "Block all removable devices for all users" and click ok. I think I had to replug the devices to get them to connect again, but I was fine from that point. Annoyingly it spells this out when you turn the feature off and then back on, but makes no mention of it during install.

 

[davidjames1701]

It's been sorted ! First of all, I'd like to thank everyone for their help and apologies from me for not thinking smart enough about this, my iMac had had a service, internal cleaning etc & a wipe for a fresh clean install of Sequoia which I noticed there was a update to Tahoe, first thing I did on Tahoe was to install my Eset Cyber Security, which I'd used for years, but didn't suspect this causing a problem, and no clue from Eset, I noticed a post on the Apple Comunity Forum saying what to do - Eset Help which explains in Eset, to go to Protections, Device Control, slide that slider to the left (its on as a default) then go to Disk Utility in Tahoe and mount each drive, they all appear instantly, all file formats, even ex-fat, I'm guessing that most security packages may do this as well, thanks again guys !

 

[schmalen]

[FIX] Time Machine Volume not mounting automatically on macOS 26 Tahoe (M2/M3/M4)

Thread Content:
The Issue:
Since updating to macOS 26 Tahoe, my external Time Machine drive (APFS Case-sensitive) no longer mounts automatically after a reboot or when re-plugging the USB cable. While Disk Utility often fails to mount it, a manual terminal command via diskutilor mount_apfs works. It seems macOS Tahoe has a bug in its mount prioritization or a conflict with TCC (Transparency, Consent, and Control) security rules for backup volumes.


The Fix:
I’ve created a workaround using a custom LaunchDaemon that triggers a mount script with a specific hardware delay and active path monitoring for /Volumes.

---

Step 1: Create the Mount Script
Create a file at /usr/local/bin/mount_tm.sh:

bash
#!/bin/bash
# 1. Hardware initialization delay (Essential for Tahoe/M-Series)
sleep 15

# 2. Ensure mount point exists
/bin/mkdir -p /Volumes/TimeMachine

# 3. Mount via Volume UUID (Get yours via 'diskutil info /dev/diskX')
/usr/sbin/diskutil mount -mountPoint /Volumes/TimeMachine 2A3947B9-72F8-4EC2-9327-BF9368CA0F40




Crucial: You must set the correct permissions and remove the quarantine flag:

bash
sudo chown root:wheel /usr/local/bin/mount_tm.sh
sudo chmod +x /usr/local/bin/mount_tm.sh
sudo xattr -c /usr/local/bin/mount_tm.sh

---

Step 2: Create the LaunchDaemon Plist
Create the plist file at /Library/LaunchDaemons/com.user.mount_tm.plist:

xml
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "www.apple.com">
<plist version="1.0">
<dict>
<key>Label</key>
<string>com.user.mount_tm</string>
<key>ProgramArguments</key>
<array>
<string>/bin/bash</string>
<string>/usr/local/bin/mount_tm.sh</string>
</array>
<key>RunAtLoad</key>
<true/>
<key>WatchPaths</key>
<array>
<string>/Volumes</string>
</array>
<key>StandardErrorPath</key>
<string>/tmp/mount_tm.err</string>
<key>StandardOutPath</key>
<string>/tmp/mount_tm.out</string>
</dict>
</plist>

---

Step 3: Activation & Permissions
For this to work on Tahoe, permissions must be exact:

1. Set Plist permissions:
   sudo chown root:wheel /Library/LaunchDaemons/com.user.mount_tm.plist
   sudo chmod 644 /Library/LaunchDaemons/com.user.mount_tm.plist
2. Register the Service:
   sudo launchctl bootstrap system /Library/LaunchDaemons/com.user.mount_tm.plist
3. Full Disk Access (Mandatory):
   Go to System Settings > Privacy & Security > Full Disk Access and add /bin/bash to the list. Tahoe will block background mount commands otherwise.

---

Results:
The drive now mounts reliably ~15 seconds after login or immediately after plugging it in. The WatchPaths trigger ensures that the system checks for the drive whenever there is activity in the /Volumes directory.
Hope this helps anyone struggling with persistent mount issues on the latest macOS!

Disclaimer:
The codes and instructions provided here are to be used at your own risk. I assume no responsibility or liability for any data loss, system errors, or hardware damage that may occur from following these steps. Please ensure you have a current backup of your data before making any modifications to your system.