Let me help you with this.
Please note the RAID BIOS or Option ROM will be enabled automatically when the chipset mode is set as RAID and by doing this the raid volume will be recognized as well.
It is necessary to set the chipset mode as RAID so you can configure and setup a volume.
I have set up the os in ahcj mode thinking that the system matrix would create a raid but have been informed that ahci dose not work that way
Yes I am afraid to say that RAID is possible when having AHCI chipset mode set.