Unable to replace failed disk
One of the 4 disks is missing. the failing disk is likely causing panics. SoftRAID has been alerting you for a couple months that a disk was failing.
Can you get the 4th disk to appear in SoftRAID? I would try without the failing disk connected, as it is making your system unstable. It seems like your volume has been unmountable since August 9.
Correct - one of the four disks is missing and is not recognized by the system - and causes the system to crash. Even if it is the only disk attached. The other 3 (including the one with predictive failure) do not cause the system to crash. The issue started occurring on the 9th of August, when the missing disk died, prior to that disk dying the volume had no issues.
The expectation of this volume completely losing a disk is that SoftRaid would not split the volume/mirror and that I would be able to remove the missing disk from the volume and add a new disk and rebuild the volume.
Normally that would be the case. Something else must have happened when the disk failed. Let me see what we can do.
Are you backed up?
This is primarily my backup target and also some archived data. It would not be the end of the world if I lose the data, but I would like to make every effort to attempt to rebuild. Maybe a learning opportunity in case this issue comes up again in the future.