$ docker run --rm --volumes-from [DATA_CONTAINER_NAME] -v $(pwd):/backup ubuntu tar cvf /backup/backup.tar [/path/to/the/data/to/backup]
$ docker run --rm --volumes-from [DATA_CONTAINER_NAME] -v $(pwd):/backup ubuntu bash -c "cd [/path/to/datadir] && tar xvf /backup/backup.tar --strip 1"