Mac OS Sequoia not recognizing USB Flash Drives

I have a similar issue with M1 Air and Sequoia (after updating), my external SSD in a HUB is not mounting.

The fix is to activate the option in security, always ask to connect accessories. Not ideal, because now a I have to allow everything I plug.

Anyone running into this issue, please open the System Information app by:

• Holding the Option Key
• Clicking the Apple logo on the top left
• Click "System Information"
  • If your issue is with USB devices and card readers, click USB and report if the USB device in question shows up.
  • If your issue is with the built in SD card reader, click Card reader.
• Screenshots of this page will be helpful.

Please also tell me the following:

• What device you are trying to plug in, model and brand
• How the drive is formatted (NFTS, exFAT, FAT, Mac OS, etc)
• How it's plugged in (via a simple USB-C adapter, or USB-C Hub)
  • The brand and model of the adapter or hub
• Have you done a clean install of Mac OS Sequoia, or an upgrade over Sonoma.

If you have issues, try a reboot and report if that fixes the problem.

• I have personally witnessed Disk Utility stop working, if a previous formatting operation failed. Only a reboot would make disk utility work again.

Try booting into recovery and see if the device shows in DiskUtility

• These Steps are for Apple Silicon (M1-M3)
  • Shut down your Mac
  • Hold power button until you see Startup Options
  • Enter your password
  • Open Disk Utility
  • Report if your device shows in recovery mode.

Sorted now. Erased HD and reinstalled Sequoia, migrated data and loaded apps manually from Adobe etc. Mounts all USB drives and XQD and SD cards in seconds. This method although tiresome, eliminates old bits of stuff that was conflicting with sequoia.

This has been my experience too since updating to Sequoia. Whether it be External SSDs, USB sticks, if the connector is of the A-type then it just won't mount. only if i use a usb-C type connector does it mount. They're cheap to buy so not a real big deal but it should be fixable by apple.

I had to go through Apple Support. They say they don't have any history of this issue with updating to Sequoia.

After trying many things, the support person had me upload the files from my Flash drive to my old computer, then using my MacBook Pro to erase my flash drives (that were already in FAT-32) and reformat my Flash drive with ExFAT. And finally, reload my flash drives with the files from my old computer.

It seems like a lot to have to go through for a system update. Especially for someone like me, who has a very basic understanding of how tech works. Trogander, you lost me on step 3 but I do appreciate all the detail you provided.

I’ve replied elsewhere? But- click ‘about this Mac’ system info >USB> and ‘if’ it’s there click on the drive for a pop up asking for permission.

after the first instance, the pop up has appeared when I connect another drive once or twice, but they aren’t hiding anymore- it didn’t appear in Disc Utility originally either.

PVRP wrote:

I have a similar issue with M1 Air and Sequoia (after updating), my external SSD in a HUB is not mounting.

The fix is to activate the option in security, always ask to connect accessories. Not ideal, because now a I have to allow everything I plug.

Once it asks about the one device, you can set that back to something else. It should remember the devices you approved.

USB C adapters got my web camera working, too. All USB devices are plugged in to a USB dock that is connected via a USB C adapter. Working fine, now. Apparently the bug is in the regular USB port drivers.

my external drives exhibits the same problem, but it's okay if i use a USB-C adaptor OR I reboot with it attached - and it mounts. By the way this only happens with my M1 Macbook Pro, does not happen with my M4 Pro Mini

Hey everyone,

I recently encountered a strange issue where my Mac M1 running Sequoia 15.2 suddenly stopped recognizing my Sandisk USB external drive.

Background:

• My external drive has both built-in USB-A and USB-C ports. Courtesy SANDISK USB A on one side USB C on another side.
• I had a Type C to Type A extension cable lying around just in case
• I had been connecting External Drive to the Type-C port on the back of my iMac without any issues.
• The problem started after I connected my iPad to the iMac.
• I initially suspected the drive had crashed, but it worked fine when connected to my MacBook Air M3.
• Command-line tools mentioned in forum didn't work.
• System Report however showed SANDISK External Drive information. (System Report is in App Launchpad with Disk Utility)

The Solution:

After some troubleshooting and watching Youtube, I discovered the issue:

• Connect the drive using the Type-A port instead of Type-C.
• Use the extension cable Type-C to Type-A adapter to plugin SANDISK Type A side (remember I said i had two--back to back).

This simple workaround resolved the issue for me.

Possible Explanation:

I suspect this might be related to Apple's transition to a more USB-C-centric ecosystem, potentially influenced by EU regulations. It seems like some USB-C devices might have compatibility issues with certain configurations.

If this solution works for you, please leave a comment and let others know!

Disclaimer: This is just one user's experience. Your mileage may vary.

I hope this helps!

PS: This post reflects the user's experience and potential explanation. It may not be the definitive cause or solution for all users.

Disclaimer: This post expresses the user's opinion and may not reflect official Apple policies or statements.

Hello people of the world,

I was able to connect external SD card to my M1 mac using a following workaround.

diskutil list

This allowed me to see IDENTIFIER of the drive

diskutil mountDisk /dev/diskX

Where X diskX is value found in terminal - IDENTIFIER

That mounted a drive and I was able to drag n drop.

Be well, I found this on reddit, user u/wowza42 mentions this 4! months ago.

I hope iCloud security team has a different management :D

I had to go dig into the sofa cushions to find a USB stick to try.

When I plugged it in, Finder gave me the this disk not recognized dialog. Figured it was just bad.

Tried formatting and then it worked fine. I don't know how it was formatted before.

If you can actually mount the drive using Disk Utility or Terminal, copy the data off and reformat. If it is a camera card, use the camera to format it.

I'll dig through some other furniture to see if I can find another to test.

I have been using SD cards on my M2 MacBook Pro without issue. The USB Stick I tested was on an M1 Mini.

I have found that USB sticks formatted for FAT mount reliably but ones formatted for exFAT don't.

Open Disk Utility, see if the USB drive appears here even if it doesn't show up on the desktop or in Finder. Disk Utility can repair or reformat the drive with corrent file system, so the it can be recognized. Note: reformatting will wipe the files in the USB drive, operate with caution.

I have had this issue, in particular when I try to dump a .stl file for my Prusa Printer, which ONLY reads a Fat32 formatted USB. I will put a small, empty Fat32 USB drive in my M2 MacStudio running Sequoia 15.0 and if I try to copy anything from a 1k text file to a 50Meg .gcode file my Mac pukes and says there is no room on the drive. I have tried reformatting using Disk Utility to no avail. But..... I have succeeded and now use Path Finder from Cocoatech and that works perfectly. I have always used Path Finder off/on and I like it for some specific things. Now it is invaluable so I can work interchangeably with Fat32 USB drives. BTW, I saw this too on my old MBP which was the last Intel MB Apple made running both Ventura and Sonoma and they did not like Fat32 drive too. I don't know of an Apple solution to this issue. While one may exist, I can say that Path Finder works every time.