Thanks for taking the time to run this test. You have been able to confirm a lot of things the problem is
not.
It is:
- Not the computer
- Not the OS kernel
- Not softraid
- Not the USB device
- Not the data structures stored on the USB device
- Not your mount command
We have also learned, apparently, that the flashing LED on that USB device does not indicate active I/O, since you were in single-user mode. Once the mount completed, no process was running except the shell, sitting idle waiting for interactive input with a # prompt.
What are we left with, then, as a possible problem cause?
The processes you are running when in multi-user mode.
Is it one of your fleet of automounting daemons? I thought so before, and your test seems to have confirmed it.
To test this, try disabling them and rebooting, instead of stopping them. Stopping them didn't seem to eliminate the problem previously.
Code:
# rcctl disable amd
# rcctl disable toadd
# rcctl disable hotplugd
If, after reboot, you are able to successfully mount the file system, you will know your root cause is how one of these daemons is configured.