So it is a local drive as opposed to network storage. What I don't understand is, you have to mount is somewhere in the file system, for example '/dev/sdd1 /mnt/raid [options]' in /etc/fstab. If you then create a directory /mnt/raid/moodledata, you can make $CFG->dataroot='/mnt/raid/moodledata'. That doesn't stop you creating /mnt/raid/somethingelse.
About the soft link, I don't know who advised against it. I can't comment because I've never created a moodledata that way.
Whatever you do, or don't do, you have to take a site-backup and test it by restoring to another location!