Mac Mini mounts 2 hard drives

Mi mac Mini always mounts 2 hard drives. I dismount the "ghost" one but next time I turn it on, there it is again, Macintosh HD2. How can I keep it from mounting a hard drive that does not exist?

Open your Disk Utility application (Applications -> Utilities -> Disk Utility) and tell us how many hard drives does it "see" and the names of them.

Here you go:

And is this the 2.0 Ghz Core i7 with OS X server installed on it from sometime in 2011 -2012?

If so, it shipped with two 500 GB drives in it.

What makes you think it is a ghost drive?
What happens when you select each of the 2 partitions there in disk utility - what sort of used/free space does each one show?

As noted in the previous reply, your Mini has two hard drives, obviously ordered that way and so shipped. One of the drives has the server version installed.

Indeed guys. The computer came with 2 hard drives. I worked in the graphic arts industry for 17 years and never saw it, nor I see the need to do it. I'd rather have one hard drive with one TB. It simplifies things for me.
Thanks.

have a look at the second video from OWC on replacing the drive/s.

How to Upgrade Aluminum Mac mini Hard Drives or SSDs @ EveryMac.com