or download this
[admin@kvm5a ~]# rbd showmapped | perl -pe 's/^?!\d+\s+.*\n//g'
id pool image snap device
0 rbd_hdd vm-209-disk-1 - /dev/rbd0
...
7 rbd_hdd vm-138-disk-1 - /dev/rbd7
8 rbd_hdd vm-141-disk-1 - /dev/rbd8
9 rbd_hdd vm-143-disk-1 - /dev/rbd9