Intel® Embedded Server RAID Technology 2 (ESRT2) RAID 5 option is grayed out for Intel® Server Board S1200SP family

What am I seeing?
On Intel® Server Board S1200SP family, the RAID 5 upgrade key RKSATA8R5 is installed but RAID 5 option is still greyed out in the  Ctrl-E RAID BIOS (also know as the Intel ESRT2 configuration utility for legacy boot mode).

Why am I seeing it?
RAID 5 is not supported when using legacy BIOS mode on Intel® Server Board S1200SP family. Refer to 3.4.3.2 Intel® Embedded Server RAID Technology 2 (ESRT2) section of the Technical Product Specification for Intel® Server Board S1200SP family:

How to fix it
Follow below steps to change the system boot mode from legacy BIOS to UEFI:

1. Ensure that the drives are connected to the corresponding SATA ports.
2. Restart the system into the BIOS.
3. Once in the BIOS, proceed as follows:
   1. Go into the Mass Storage Controller Configuration menu and see to it that both AHCI Capable SATA Controller and AHCI Capable RAID Options are set to RAID Mode and Intel(R) ESRT2, correspondingly.
   2. Go into the Advanced Boot Options menu and change Boot Mode to UEFI:
      
   3. Save the changes and exit.
   4. Restart back into the BIOS. Once back into the Set-up Utility, proceed as follows:
      1. Go into the PCI Configuration menu, and then go into the UEFI Option ROM Control:
         
      2. Once inside the UEFI Option ROM Control menu, go into the Intel(R) Embedded Server RAID Technology 2 (in the screenshot below) and follow the on-screen instructions to create the RAID 5.

         For more details, refer to the Human Interface Infrastructure Configuration Utility section of the Intel® Embedded Server RAID Technology 2 User Guide.

4. Save the changes, exit, and proceed installing the operating system as normal.