I have a computer with one 250GiB SSD disk connected to first onboard SATA connector which holds one EFI partition and one root partition (ubuntu 19.04).
The computer also has a second discrete SAS controller card in a PCIe slot with 4 x 500GiB slow disks attached.
The slow disks are in an enclosure that supports hotswap. I installed the OS while the 4 slow disks were not enabled. Ubuntu installer puts UUID numbers in /etc/fstab nowadays so I was a bit suprised that the OS completely locks up and fills the screen with filesystem errors for the ubuntu root partition as soon as I enable one of the slow disks. It seems as though suddenly the kernel confuses the newly enabled disk with the existing one even if the slow disks have been completely wiped.
I could go on listing all manner of log output, but copying it is difficult as the computer locks up completely and won't even reboot on 3 finger salute. I have to power off. Though it looks exactly as it would look if you yanked the SATA cable oout of the disk while the computer was booted. Not pretty.
I am curious if there exists any theories on why this would happen, and how I might go about debugging it further!