You can switch the P420i card into IT mode (plenty of guides on the web), then it will stop being a RAID controller, and your individual disks will appear in unraid. You’ll need to tweak the drive config in unraid to get the individual disk temperatures showing correctly, but other than that it should work perfectly (of course, using another HBA card will also work but you’ll need to buy longer mini SAS cables as the internal cables aren’t quite long enough, also the drive LEDs may not work either, it depends on the HBA card firmware IIRC)