I am setting up a NAS device using an Intel 1200 BTSR motherboard and an Areca 24 port SATA/SAS card. Booting up into the Areca card's BIOS, I'm able to see all 20 drives that I have configured in JBOD mode. Booting into the motherboard's BIOS only shows 15 of the drives plus the SSD connected to its on-board SATA port. It looks as if that's all the MB BIOS is presenting to the OS, as neither FreeNAS nor various Linux flavors see the full complement of 20 disks.
How can I get the OS to see all 20 disks connected to the Areca card?