I am trying to install CentOS 7.6 to a R740XD server. The server has eight 1 terabyte drives in the front bay, and two 600 gig drives in the back bay. I want to configure the two 600 gig drives in a RAID 1 configuration and install the OS to that drive, and configure the eight 1 terabyte drives in a RAID 6 configuration to use as data storage. I configured the RAID 1 and RAID 6, installed the OS to the RAID 1 drive, rebooted, and got an error about no OS installed. It was looking for an OS on the RAID 6 drive, so it appeared that the BIOS was seeing the RAID 6 as the first drive in the system, and failing when no OS was found there. I removed the RAID 6 configuration, installed the OS to the RAID 1, and the system booted correctly, but after configuring the RAID 6 again, it tried to boot from that drive, rather than the RAID 1, and failed. I tried to edit the boot sequence to have it choose the RAID 1 as the first device, but the BIOS only sees the RAID controller as a single device, not 2 separate drives. The PERC controller is a R740P-Mini. I'm using legacy BIOS, not UEFI. How can I force the system to recognize the RAID 1 as the first hard drive, and not the RAID 6? Thanks