ReadyNAS 314 Largest Hard Disks installed?

ReadyNAS RN-314

Please can anyone advise what the largest drives are that they have employed in this or similar NAS units I'm utilising the last latest firmware that was available for this system. Without looking I think it was FW Version: 6.10.10

I current run 4No. Seagate EXOS 18TB disks in the unit and I'm looking to upgrade them to 4No.  EXOS 24TB disks. I don't recall these being on the approved list as they came along after this unit was discontinued... however they work just fine. 

Thanks for any advise.