docker volume create mariadb-volume
The volume data is stored under the /var/lib/docker/volumes
on your host.
docker run -d --name mariadb -p 3306:3306 -e "MYSQL_ROOT_PASSWORD=YOUR_ROOT_PASSWORD" --restart unless-stopped -v mariadb-volume:/var/lib/mysql mariadb:latest
Don't forget to replace YOUR_ROOT_PASSWORD
with your secret password.