The X79 Dark has 2 seperate RAID controllers, an Intel that is integrated to the in the X79 south bridge, the secondary is a Marvell.

First off, remember that a RAID array is isolated to a specific controller so you can NOT make one large array across ports controlled by the Intel and Marvell together through the controller.

To access the Intel controller, first, you MUST have 2 or more HDD/SSD's attached, have them enabled in the BIOS and have the BIOS set in RAID mode.

Save and Exit the BIOS

Upon reboot, there will be the initial POST screen, after that you will have a secondary black screen showing initialization of the SATA controllers, at this point press CTRL-I this will allow you to go into the Intel Controller.

If you do NOT have 2+ drives plugged in and RAID mode enabled, the option to enter the controller will NOT be available.

For the Marvell controller, you can access as long as 1 HDD/SSD is plugged in, and that is accessed at the same point of POST by pressing CTRL-M