Multi GPU and Deadline

[zoubein]

Hi

We have a small farm with a few boxes with 4 cards each, and we are rendering using Maya and Arnold GPU to render through Deadline. A bit confused with the way Arnold GPU uses the cards we are not using NVLINKS so will Arnold use all 4 cards to render a frame or will it just use one card since we dont have NVLINKS?

Cheers

[Stephen.Blair]

Arnold GPU will use all the cards, but memory won't be shared.
The full scene will be loaded on each card.

[zoubein]

Thanks, so is it a good investment to get some NVLINKS? will we see some speed gains?

[Stephen.Blair · Accepted solution]

Not necessarily speed, but you'll be able to render larger scenes. Memory will be pooled across the card.

If I have multiple GPUs, will Arnold use them all?

Arnold will use all the GPUs at full capacity yes. It will also pool the memory if you have NVlink. However, you can only Nvlink 2 cards together at the same time. So your memory is bound by these "islands". One possible limitation of using differing RTX GPUs at render time is that the less powerful GPU may end up throttling the more powerful one as the work is divided between the GPUs evenly.

If I have three cards, how much memory will I have?

You can NVLink two cards, so your memory limit is determined by the third card. For example, if you have three cards with 16GB, the scene and textures have to fit in 16GB. The two NVLink cards combine for 32KB, but the third card is still 16GB, so the limit is still 16GB. Three cards are still faster than two, so it's a tradeoff.

If I have two cards that are not NVLinked, is a scene split across both cards?

The scene must fit on each card. For example, if you have two cards, each with 16GB, then the scene must fit in 16GB. Each card loads its own copy of the scene.