On R1304GZ4GC, the backplane is connected to the onboard SAS/SATA capable ports, or SCU ports. You need to go to following BIOS menu: Advanced => Mass Storage Controller Configuration => SATA/SAS Capable Controller. Choose either ESRT2 or RSTe mode. The drives connected to SCU ports won't show up in BIOS, but you should see them in the RAID configuration utility.
See Intel® RAID Quick Reference Guide for more information about onboard RAID.
As for the 4TB SATA HDD, you may want to check the hardware compatibility first. Please take note that UEFI boot is not supported on ESRT2, and Linux is not supported on RSTe. See Errata 1-3 of the Monthly Specification Update for details.
I knew Linux has mdadm utility and driver for RSTe. Can you help to confirm the above statement is still valid in today newer Linux OSes? Is the above applied to those old OS with kernel below 2.6?