If you want to see how a large copy is proceeding you can send -USR1 to the process.
# dd if=a.img of=/dev/libvirt_lvm/a-os
In a new terminal send -USR1 to the process or even use watch if you like.
# watch -n60 'kill -USR1 $(pgrep ^dd)'
The copy will start showing some progress lines after each -USR1 received.
6370041+0 records in 6370041+0 records out 3261460992 bytes (3.3 GB) copied, 247.17 s, 13.2 MB/s