Copying data with dd can take a very long time and the process could seem to be frozen. To see status messages from dd you can use the following command:
pkill -USR1 -n -x dd
This will output something like below in the original terminal where dd is running:
559+0 records in 559+0 records out 2344615936 bytes (2,3GB) copied, 150,144 s, 15,6 MB/s
To see status updates repeatedly watch is very handy:
watch -n 10 "pkill -USR1 -n -x dd"
This outputs a status message like above all 10 seconds.