My understanding is that RAID is typically controlled at the hardware level by the disk controller. So, in your example, the two disks that are used as D would need to be on one controller (say as a stripped or mirror set). The system would need to be configured so that those disks are not expected to provide the primary (boot) partition.
You ask what RAID format to use. Suggest you understand what the different RAID formats are (see click here) and decide what you want to achieve first. In any event, you will be limited by the RAID formats supported by your controller.