Samsung SSD suddenly isn't readable and won't run first aid

Make sure Sonoma is completely up to date with all patches....I think it is up to 14.1.2 at this time.

Unfortunately First Aid doesn't specifically mention the specific error nor is it easy to find the meaning of exit code 12. Since it is an exFAT volume, you could try running a file system check using Microsoft Windows to see if it can repair it.

I hope you have a backup of the data on this drive. It is hard to say what may have caused the file system corruption. If MS Windows is unable to repair it, then you will need to erase this drive and restore the files from a backup.

What file system is on the T7?

Try running First Aid a second time immediately after the first scan fails. Sometimes this will allow the scan to complete successfully.

Click "Show Details" on the First Aid summary screen. Post the First Aid report here.

Get (try) a current backup if you don’t already gave one, then check for diagnostics and recommendations from Samsung support, then (if you can get the SSD working stably and have a backup) apply the most current SSD firmware if not already loaded.

Peter Tompkins wrote:

I have an old Mac with Monterey 12.6.3 OS and my Samsung T7 Shield mounts! This is an apple issue on the new versions of their OS.

Check for diagnostics, for firmware updates, and then check with Samsung support for related reports.

While this might be macOS, it might also be some Samsung issue.

And if it is a macOS issue, Samsung would be in the best position to know about and discuss that with Apple, and to potentially work around the issue.

And get a backup, if the data is valuable and there’s no current backup.

I'm having the exact same issue with my Samsung T7 Shield. It use to connect fine. Now none of my macs can see the SSD.

I have an old Mac with Monterey 12.6.3 OS and my Samsung T7 Shield mounts! This is an apple issue on the new versions of their OS.