I'm in the process of building a NAS, and went with the Asrock Rack x470D4U motherboard. I was unsure about it supporting re-bar. After tearing trough the BIOS, I was a bit annoyed when it was not supported. I ended up sending a mail to Asrock rack...

To my surprise they answered a day later with a BIOS update:

We add resized bar option in BIOS L4.27
Advanced -> PCI Subsystem Settings -> Re-Size BAR support.

The BIOS is not listed on Asrocks pages yet, so you should probably not use it yet. (Especially not since you got the file from a random guys blog).

But if somebody needs it, here's the file:

Other names for resizable bar:

  • CAM - Clever Access Memory
  • SAM - Smart Access Memory
  • Rebar - Resizable bar