# An Intel Arc GPU gets its full VRAM on a 2015 Xeon

A boot-time tool called arc-rebar tricks old motherboards with no Resizable BAR option into exposing an Arc card's full VRAM. One test went from 15 GB/s to 392 GB/s.

- Category: Hardware (mod)
- Made by: [Rod Burlamaqui](https://github.com/RodBurlamaqui/Intel-ARC-Rebar) on GitHub
- Original: https://github.com/RodBurlamaqui/Intel-ARC-Rebar
- On Afterware: https://afterware.xyz/p/an-intel-arc-gpu-gets-its-full-vram-on-a-2015-xeon

## Can I build this?

- Difficulty: Beginner
- AI-buildability: 5/5 (It's a software-only boot hook installed on a Linux system you already have, so it's mostly running diagnostics and scripts, with no hardware work.)
- Time: An evening
- Cost: $0
- Parts: Intel Arc B580
- Tools: Debian or Ubuntu system, terminal

Estimates based on the original write-up. How the AI-buildability score works: https://afterware.xyz/ai-buildability

## Build sheet

- Board: Supermicro X9DRH-7TF
- GPU: Intel Arc B580 12 GB
- OS: Debian 13, xe driver
- Method: initramfs boot hook

## Starter prompt

```
Based on "An Intel Arc GPU gets its full VRAM on a 2015 Xeon" on Afterware: https://afterware.xyz/p/an-intel-arc-gpu-gets-its-full-vram-on-a-2015-xeon

I have an Intel Arc GPU in an older motherboard with no Resizable BAR option in the BIOS. Help me check the kernel log for the "Small BAR device" message, then write an initramfs hook for Debian that resizes the GPU's BAR2 to the full VRAM size before the xe driver loads. Include a verification step that reports the new Vulkan heap size.
```

## Story

Intel's Arc cards are designed to map their whole video memory into the PC's address space through Resizable BAR. Boards without that BIOS option only expose a 256 MB window, so big allocations fail and data crawls through the gap. On a 2015 Supermicro X9DRH-7TF with two Xeon E5-2670 v2 chips and an Arc B580 12 GB, the 4K Vulkan filter test went from stalling at zero frames to 39–50 fps.

Rod Burlamaqui's arc-rebar runs from the initramfs on every boot, before the xe driver loads. It writes one PCI register and re-enumerates one PCIe root port, leaving the firmware, kernel and Intel's drivers alone. It ships with diagnostics that check the kernel log for the "Small BAR device" message and the "was not released" bridge signature, so you can tell whether you have the problem before you touch anything.

If you have an old Xeon or Core board gathering dust with an Arc card in it, this is the rare fix that costs nothing but a reboot. The project is free for personal use, requires Debian or Ubuntu, and the author says to back up first.

## Resources

- [arc-rebar GitHub repo](https://github.com/RodBurlamaqui/Intel-ARC-Rebar)

Tags: intel arc, resizable bar, pcie, linux, debian, xeon, gpu

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