[blue68f100]

The 4500 does support the 750gig HD's, atleast with v4 GOS. The Dell and 4200 are different. They look the same with on minor difference. The 4200 has a ID chip that identifies it as a Snap unit. This is required for GOS.

There is a thread where FreeNAS was installed on a 4500. There was one issue that needed addressed.

The bios should see all HD, not that it is required for a linux OS. It does it own discovery process. I would swap drives and sleds to see if you have a hardware problem the reason in only see 2 HD's.