Docker Swarm - no space left on Worker-Node even if each volume is with NFS

Hi All,
I’ve setup an infrastructure for our company’s websites with docker swarm (for now we are testing it with only 2 nodes: one manager and one worker. I know that is too little, but now its only for testing).

For now we have 10 stacks (3 on manager, 7 on worker)

Every container running on the worker-node has its storage volume mounted from an NFS server.

The total amount of the GB for all the stacks on the NFS server is 5GB.

Now, I don’t understand why the worker-node has filled 11GB on its hard disk…

The only bigger folder that i see on the worker node is “/var/lib/docker/overlay2/”…

How its possible??

Here some info:

– Ubuntu 18.04
– Docker version 18.09.6
– NFS docker-compose.yml config example:

volumes:
  www:
    driver_opts:
      type: nfs4
      o: addr=192.168.1.13,nolock,soft,rw
      device: :/var/nfs/storage/website_1/www