$ mount /dev/mapper/docker-8:1-3146939-pool /mnt/docker-data/
mount: wrong fs type, bad option, bad superblock on /dev/mapper/docker-8:1-3146939-pool,
       missing codepage or helper program, or other error

$ lsblk --fs
loop1
└─docker-8:1-3146939-pool
loop2
└─docker-8:1-3146939-pool