how to do hardware raid on dell r720 server

hi

I have one r720 fully populated with HDD, I have two logical drives 0 and 1, the first logical drive ( 6 units of 500GB HDD) is configured with raid 0 and contains data, the second logical drive has only 2 units of 500GB with raid 1 configured on it and also its hosting the operating system. My client populated the 6 units with the data first and the last two with the operating system as the last HDD. During boot operation I have the following error 1. No boot device available 2. Current boot mode is set to bios 3. Please ensure compatible bootable media is available 4. Use the system setup program to change the boot mode as needed.

I tried using the system setup program to change the boot mode at the bios by pressing f2 function key. I have two options on boot mode ie the bios and the UEFI. When I change to UEFI I was redirected to boot from NIC or DVD rom, when I change back to bios I have the same error above, how will I change the settings such that my server will not look for the boot sector from the first two hard drives or rather  how do I redirect it to boot from the last two HDD having my operating system. My fear is losing data on those first logical drive.

Best Regards,