Set up RAID 1 in Mojave

I just got a new G-RAID Thunderbolt 3. How do I set it up in a RAID 1 with a Mojave iMac?

Actually, I see that you can use the RAID assistant in Mojave’s Disk Utility, but in order for it to work, you have to partition the drive into two. If I’m partitioning my 16TB drive into two 8TB sections, how do I know that the partition is going along with the two separate 8TB physical drives in the unit? And does matter if the partition goes along with the physical drives, or if its elsewhere?