Ok, so that confirms that your Ubuntu root is on /dev/sda2.
Could you now run:
sudo fdisk -l /dev/sdb
I am hoping this will yield more information about that second disk.
The smartctl will show errors on a disk, for example:
sudo smartctl -x /dev/sda
sudo smartctl -x /dev/sdb
However, looking at posts #7,8 and 9, it sounds like the result might be predictable….
That does assume, of course, that the drive supports SMART.