You are right. That's exactly the problem...

The “Intel ® Virtual RAID on CPU” BIOS menu should be used to create the desired
RAID volume(s). Currently supported RAID configurations are:
• RAID 1 boot volume.
• RAID 1 data volume.
• Only 1 volume is supported on a given array of drives. Matrix RAID is not
supported.
• RAID 0/10/5 are not currently supported.

Thanks for the hint