External hard Drive Invisible on Mac Mini used as a file server

We're using a Mac Mini as our small office file server. There are multiple external Hard drives connected. All of the drives show up and are accessable on the networked computers but on the Mini itself, some are only accessable through Disk Utility. The inaccesable drives are not on the desktop nor in the sidebar in Finder. Some drives show up on the desktop and finder. The Finder preferences to display external drives on the desktop is checked. I have tried using sudo chflags commands to make the drives visible. Nothing has worked. The only place they show up on the Mini they are physically connected to is in Disk Utility.