Mounting two external block devices as persistent storage

I read the tutorial on how to mount ext4 block devices as persistent storage by stopping Docker, mounting the device as /var/lib/docker and restarting Docker. So far so good. But what if you want to have more than one external filesystem on the host as persistent storage? Where should I mount that so the overlay2 storage driver knows what to do with it?

Hmm. I mounted it under /var/lib/docker/data and it doesn’t seem to complain.