you should leave the Bios defaults to Raid+AHCI, as this setting is the most compatible/fastest for the z420
the raid extensions by default contain the AHCI driver, and the raid bios will only be loaded/used if you create a raid array otherwise it's not loaded and only the AHCI extensions are active
new drives are usually pre partitioned and formatted as Fat32 and should be reformatted as NTFS using "disk Management"
disk management will also show if the drive has been partitioned, if not then partition and format
https://www.digitaltrends.com/computing/how-to-partition-a-hard-drive-in-windows/
https://www.wikihow.com/Partition-Your-Hard-Drive-in-Windows-7