This message was posted on behalf of Intel Corporation
I understand you are testing the onboard RAID controller on RAID 1.
I was thinking that Asus has modified this configuration at RAID BIOS level, it appears to be that this RAID 1 volume recovery will only work if failed drive is set on SATA 0.
Theoretically, the SATA drive port should not matter but this seems to be customized by Asus.
I recommend checking with them for further information.
See contact information here
Hope this information is helpful.
Please do let me know if you need further assistance with your Intel product, I will be glad to assist you.