Getting failed message when trying to create symlinks. It seems there should be another field for the name of the symlink in this feature as well.
ln -s pathtolink nameoflink (created in destination folder)
So if you wanted /opt to be included in folder data on data disk...
ln -s /opt opt (created while in this location /media/uuid/data)
Source: /opt
Destination: /media/uuid/data
Name of symlink: opt
After which you should be able to:
cd /media/uuid/data/opt
ls -la (to see contents of opt.)