Multiple graphics cards questions.

Support Technical Support
1

I have been researching doing multiple graphics cards but I am confused on some things.

  1. Does 2 identical cards double the memory capacity for the scene? I have setup CPU render networks for Vue. In that setup, the entire scene is sent to each PC so each PC needed to have enough RAM for the entire scene. Is it that way with multiple graphics cards too where the entire scene would be loaded on each card?

  2. Is there a memory limit in cylces? I was reading about an 8GB memory limit. Is that correct? If so, is that total scene memory or per card?

What I am wanting to do is to run 2 GTX 1080 and be able to have scenes up to 16GB.

2

The scene is loaded into the memory of each graphics card so your memory limit is restricted to the card with the least memory.

1 card with 8GB + 1 card with 1GB = 1GB memory available
1 card with 2GB + 1 card with 2GB = 2GB memory available

What I am wanting to do is to run 2 GTX 1080 and be able to have scenes up to 16GB.
Each card would have to have at least 16GB on board for you to have 16GB available.

Also note that if you have identical cards in SLI mode then you would have less performance than if they were 2 independent cards

3

Thanks for clearing up the memory question. One more question about the independent cards…

I’m assuming based on your answer that cycles can use both cards if they are set up as independent cards, is that correct?

If so, does it give the option to use both or just one? That would be the best because I could then render with only 1 card if I wanted to use the computer while it was rendering.

I just want to make sure I understand how it all works before making a very expensive purchase for to 1080 cards and a new computer :slight_smile:

4

sorry to hijack this thread, but I did a recent test render and found no difference in render times with SLI on or off, has something changed recently?

5

Hi damon, you can en/disable each card for render.
I often use one card for setup scene and preview and other card for display to work without lag in view port.

@Shonuff, SLI can slowdown performance but fine if it is not.
Main thing is Cycles does not profit from SLI.

Cheers, mib

6

thanks for the reply mib
yeah it doesn’t speed it up, which you would think SLI would do, but it doesn’t slow it down either lol

wonder if we will get a fix for this soon…

7

SLI is mostly for games, at least those games that are programmed to use it. Not only can SLI slow down renders but it takes up a small amount of card memory too. If your primary use is rendering, it’s best just to leave it off.

8

like I said, I haven’t noticed any difference in render times.

9

while on this subject, because I have dual video cards, is there any way you can use one card for rendering in blender for eg while the other I dedicate to use for editing etc? is this possible?

sorry for a noob question but first time I have had a system with dual gfx cards