Here you can set the GPUs on your system and how Octane will use them. As we mentioned earlier, Octane uses Nvidia GPU models. If you are looking for speed and performance, it is naturally recommended to increase the number of GPUs. Preferably GPU's of the same model and Vram. Remember, GPUs are also used by your operating system, Cinema 4D viewport or other softwares running on the background. So you may need to make some adjustments to get a full performance. We'll talk about these below.
The ‘Render Priority’ option is for adjusting the GPU usage. It is similar to the task manager ’CPU Priority’. This settings depends on the scene structure you have and may vary performance from scene to scene.
It shows the GPU cards in your system. From here you can determine how to control the GPUs. The settings you make here with your GPU may vary depending on the structure of your scene. Now let's look at a few usage scenarios. Finally, do not forget to activate the box next to use priority.
You have 1 GPU card and 1 Monitor:
You may add 1 more GPU. UI and Viewport feedback will be faster this way. It is also recommended to leave Render priority at "LOW" when you have only 1 GPU card.
Info: To activate the priority, press the box next to it. If this box is off, the GPU will run 100%.
You have 2 different models of GPU cards and 2 Monitors:
You can connect one of the GPUs (preferably the weak one) to the main monitor you are working with. If your scene is heavy and complicated, you can play with the weaker GPU, either from the Priority settings, or you can turn off that GPU. Also you can activate "High Priority" for the powerful GPU.
You have 2 same models of powerful GPU and 1 weaker GPU:
In this scenario, you can connect the GPU with the highest VRAM to the monitor you are working with. You can set the other powerful GPUs to "HIGH PRIORITY". If your scene is heavy and complicated, you can play with the weaker GPU, either from the Priority settings, or you can turn off that GPU.
You have many powerful same model GPU and 2-3 Monitors:
In this scenario, all GPUs will provide high performance so you can leave them all open and make "High Priority". It is also not advisable to add a weak GPU in such a configuration.
One of the questions about Octane is related to the use of Vram. Here is the magic question: "I have 2 GPU cards, one is 6 GB, the other is 4 GB, but the Octane only sees 4 GB. Octane is wrong because it should be 10 GB. Is there any information on this issue? "
Yes we have the information, let's explain: Putting two cards (or multiple cards) together will add up the cores resulting in a linear speedup, unfortunately it is not same for the VRAM -memory is not compounded in the same manner in GPU rendering.
All the textures and HDRI among other stuff used for an entire scene has to fit into a functional swap space – that is each GPU must have a copy of all scene elements it needs to process — and therefore this swap space will be limited to the size of that card with the least amount of VRAM present in your machine or in the network where all GPUs used for GPU rendering resides.
So, according to the above explanation, if you have 2 or more GPU cards, the lowest Vram amount will be used. This is a general GPU technology limit, not Octane's fault.
Look at the picture below: