I'm having difficulty setting up Docker to build a container with the XFS Filesystem. My Storage Driver is correctly set to overlay2, but my Backing Filesystem is extfs.
Is there something I would specify for storage-opts in my docker daemon file?
If you are using the overlay2 storage driver, then Docker never creates filesystems. It is simply creating directories on your existing backing filesystem. If that filesystem is using ext4, that's what you're going to get.
The only situation in which Docker actually creates a new filesystem is when using the devicemapper driver, in which case Docker is carving out chunks from a block storage device and then formatting them for use with the filesystem of your choice.