Octane Not Using Second GPU: Multi-GPU Setup Problems and Fixes

Octane not using second GPU is one of the most common multi-GPU complaints, and the manual covers most of the causes. It is rarely a mystery: a checkbox, a priority, a monitor assignment or an out-of-core lock. This guide follows OTOY’s Devices tab documentation and ends with six fixes in order. The guide uses the Cinema 4D edition of the manual; other host applications have similar pages.

Why is Octane not using second GPU in my render?

The most likely reason is a device setting. OTOY documents that the Available GPUs list shows every GPU card in the system, with one checkbox per function: Using the GPU for Rendering, Using the GPU Priority setting, Using the GPU for Tone mapping and Using the GPU for Denoising. If a box is unchecked, that GPU is not used for that function.

Source: Octane Devices tab (Cinema 4D).

How does render priority affect multi-GPU Octane?

Render Priority is set per GPU, with options including LOW and HIGH PRIORITY. OTOY suggests keeping a single GPU at LOW when it also drives the monitor, so the interface stays responsive. With several identical powerful GPUs, the page advises keeping all of them at High Priority and not adding a weak GPU to the group.

What happens when the two GPUs are different models?

Mixing cards changes the advice. With two different GPU models, OTOY suggests connecting the weaker card to the main monitor and giving the stronger card High Priority. For heavy or complex scenes, lower the weaker GPU’s priority or disable it. If you have two powerful GPUs and one weaker card, connect the highest-VRAM card to the working monitor, set the other powerful GPUs to High Priority and lower or disable the weaker one for heavy scenes.

Does a second GPU add VRAM in Octane?

No. OTOY documents that multiple GPUs increase render performance linearly, but VRAM does not add up the same way. Every GPU needs a copy of all scene assets it processes, so usable space is limited by the card with the least VRAM among the GPUs used for rendering, including networked GPUs.

The table follows the rule in the OTOY documentation. Real speed also depends on the scene.

Can out-of-core stop Octane from using a second GPU?

It can stop you from changing devices. OTOY states that you cannot turn devices on or off while out-of-core is in use, and that out-of-core memory is shared between GPUs. The same applies to network Render Nodes. If a card was disabled before the render began, it stays disabled until you stop out-of-core use.

Source: Octane out-of-core (Cinema 4D).

Six fixes when Octane is not using second GPU

1. Open the Devices tab. Confirm both cards appear in the Available GPUs list. If one is missing, the issue is outside Octane, such as drivers or the physical connection (our interpretation).
2. Check Using the GPU for Rendering. The box must be ticked for each card you want to render.
3. Check Render Priority. Set cards that should render at full speed to High Priority, and keep the display card at Low if it drives the monitor.
4. Stop and restart before changing devices. Device changes are not allowed while out-of-core is in use.
5. Compare VRAM. A smaller card limits the scene; disable it for heavy scenes.
6. Check Use RTX acceleration. OTOY says the option is enabled by default in the device settings, so confirm it was not turned off.

Related reading: Octane GPU memory error VRAM fixes, Redshift vs Octane animation stability and Maya Arnold CPU render too slow.

When a rented multi-GPU machine makes sense

If a second card in your own workstation is the problem, a rented multi-GPU server avoids the case but does not change the VRAM rule. As one example, iRender’s public price page lists 2x RTX 4090 at $15.00 per hour, or $13.50 for 3 hours or more, as of October 2026. Compare providers in the top render farms of 2026, and read the provider’s current price page before committing, since prices change.

Conclusion

Octane not using second GPU almost always traces back to a Devices tab setting, a priority choice or an out-of-core lock. Work through the checklist, remember that VRAM does not add up, and disable weaker cards for heavy scenes. If you need more memory per card, look at larger GPUs in the top render farms of 2026.

In short, octane not using second gpu is almost always a setting or a driver issue, not a hardware fault. Work through the checklist above on a short frame range, and change one thing at a time when octane not using second gpu persists.

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