MergerFS Multidisk Mount Batocera
Make required directories mkdir -p /userdata/mergerfs/VERSION_NUMBER && cd /userdata/mergerfs/VERSION_NUMBER
Download newest static mergerfs build, current built now can be found HERE
extract tar -xvzf FLIE_NAME.tgz
cd ../ && ln -s VERSION_NUMBER current
Create disk labels so we know what to add to the script, replace LABEL_NAME and /dev/sda1 with your disk info e2label LABEL_NAME /dev/sda1. Thankfully batocera mounts disks by label in the /media/ folder
Create script to mount nano mergerfs.