Rancher uses etcd as datastore. When using the Single Node Install, the embedded etcd is being used. The persistent data is at the following path in the container: /var/lib/rancher. You can bind mount a host volume to this location to preserve data on the host it is running on.

Command:
docker run -d --restart=unless-stopped \
  -p 80:80 -p 443:443 \
  -v /host/rancher:/var/lib/rancher \
  rancher/rancher:latest