You don't say which deployment tool you used to set up OpenStack, but given the content of your message, I assume you are using Kolla.
In Kolla, many services have a corresponding volume used to store persistent data. Glance has a glance volume which is used by the glance_api container for the file backend.
From inside the container, the glance service would see this volume mounted at /var/lib/glance.
I noticied in the glance configuration file after deploying openstack that filesystem_store_datadir=/var/lib/glance/images/ however, upon inspection, I found that images weren't stored in that folder, instead all images where located in this folder /var/lib/docker/volumes/glance/_data/images/.So I'm thinking if actually filesystem_store_datadir is not used to store images but maybe something else.