I once executed a command to mount a disk:
sudo mount /dev/sda3 /media/test
And noticed the following error:
mount: unknown filesystem type ‘LVM2_member’
The disk was partitioned under LVM, so to mount it you need to specify not /dev/sda3, but let’s see the correct name with the command:
sudo lvdisplay
In my case, it was /dev/ubuntu-vg/root, and mount it:
sudo mount /dev/ubuntu-vg/root /media/test
Done.