[CentOS] Centos 7 and Software Raid Minimal Install

I am trying to install Centos 7 on a couple 4TB drives with software raid. In the Supermicro bios I set UEFI/BIOS boot mode to legacy. I am using the Centos 7 minimal install ISO flashed to a USB thumb drive.

So I do custom drive layout something like this using sda and sdb.

Create /boot as 512 MB XFS raid1 array.

Create SWAP as 32 GB SWAP raid1 array.

Create / on 3.xxx TB XFS raid1 array.

I then get error.

"Your BIOS-based system needs a special partition to boot from a GPT disk label. To countinue, please create a 1MiB 'biosboot' type partition."

I cannot seem to create the biosboot partition so it is mirrored to both drives for redundancy. Any ideas how to do this? I want everything mirrored to both drives.