When the file storage backend is used, the filesystem_store_datadir configuration option in glance-api.conf declares the directory Glance uses to store images (relative to the node running the glance-api service).
$ #for RHEL/CentOS/Fedora derived distributions
$ sudo openstack-config --get /etc/glance/glance-api.conf \
DEFAULT filesystem_store_datadir
/var/lib/glance/images/
$ #for Ubuntu derived distributions
$ sudo cat /etc/glance/glance-api.conf|grep \
filesystem_store_datadir|egrep -v "^#.*"
filesystem_store_datadir=/var/lib/glance/images/
