So, how many of those 18TB drives do you have in that box?
Zero.
Those are matched external drives that I rotate in for offsite, monthly backups. I put the 12TB drives, which were my old externals, in the box. So really I upgraded from 6TB drives to 12TB for internals and those 18TB drives are my new externals. There's also a 10TB drive in the box as well for game install backups for 4 computers. There are 70TB worth of drives total dedicated to having 4 copies of my data. I use Free File Sync to mirror what's on the 12TB drives and there are 2 copies of my data on the external 18TB drives. I like having an extra copy of all the game install backups on the externals, which is why I size them larger.
From time to time I mirror the 12TB mirror and 10TB game backups to my main gaming rig, which has a 16TB drive in it, because why not go overkill on backups right? I suppose that backup is for uptime in case the server fries or something.