My B450 board with Ryzen 2700 has only 4 usable SATA ports (if a M.2 drive is connected, the SATA ports 5 and 6 are disabled) and the 4 disk scrub in FreeNAS is

My B450 board with Ryzen 2700 has only 4 usable SATA ports (if a M.2 drive is connected, the SATA ports 5 and 6 are disabled) and the 4 disk scrub in FreeNAS is fairly slow compared to the sum of the speed of each drive. Heavy FreeNAS users confirmed many times on the forum that the performance of a dedicated controller is visibly (not only benchmark measurable) better than the onboard SATA. I did not test, personally, just pointed to the FreeNAS forums.