# backup remote docker volume to local tar file
ssh USER@HOST 'docker run --rm -v VOLUME_NAME:/from alpine ash -c "cd /from ; tar -czf - . "' > FILENAME.tgz

# backup remote docker volume to local volume
ssh USER@HOST 'docker run --rm -v VOLUME_NAME:/from alpine ash -c "cd /from ; tar -czf - . "' | docker run --rm -i -v VOLUME_NAME:/to alpine ash -c "cd /to ; tar -xzvf - "

# copy local docker volume to remote volume
docker run --rm -v VOLUME_NAME:/from alpine ash -c "cd /from ; tar -czf - . " | ssh USER@HOST 'docker run --rm -i -v VOLUME_NAME:/to alpine ash -c "cd /to ; tar -xzvf - "'