On a GA-P55A-UD3 here's my dilemma:
Installed the board with a single Intel SSD and WIn 7, after setting the "PCH SATA Control Mode" to AHCI as recommended on Newegg. SSD was on SATA2_0. Win 7 installation went fine, all well, did not need to add any drivers during installation. Then added a 1TB data disk on GSATA_6. All still fine. Then took a RAID pair of disks from another machine and installed them on SATA2_1 and SATA2_2. BIOS recognized both disks, BUT Win 7 sees only one. (I disconnect one of the pair and Win 7 looks the same.) Then I try changing the "PCH SATA Control Mode" to RAID(XHD). I could get into the RAID setup by CTRL-I, both new disks were listed. So just for fun I tried leaving them non-RAID and trying to boot, but the machine would not boot. If I change back to AHCI, the system boots, but, of course, no RAID.
What I want to do is to make the two new disks a RAID 1 array, leave the SSD and 1TB drive as single non-RAID drives. Any ideas? Thanks.