Multiple GPUs with no SLI or Crossfire for rendering?

This has been asked before but it’s hard to find a solid answer that isn’t mostly speculation. I’ll give context. I’ve got a b450 f atx board that only supports crossfire but not sli. Now my plan is to either swap out my gtx 980 ti for 2x vega 56 or buy another gtx card. My question is, if I buy another gtx card, let’s say the 1070 8gb, and add it with the 980 ti with no SLI, will I be able to 1.render scenes with both cards, 2.will blender utilise the extra vram on the 1070 or will it just go with the 6 the 980 ti has making the extra 2gb vram useless? Also would it be better to use crossfire with the 2 vega or not use crossfire with them both? Please no speculated answers. Thnx

You will. But just don’t put SLI on while rendering in blender. SLI will not take advantage of that technology, nor does it need to… If you have two different cards though, you can’t use them in SLI in games either. But if your intention is only to render, you can use all cards that are supported and that you can get up and running in whatever OS you’re using. Mind you though, it will hamper the performance if you exceed the RAM usage of the card with the least RAM, that is a fact. only the RTX Series with the NVlink has the possibility to double ram when used like that. But as far as i know, blender does not support that yet. (correct me if i’m wrong.) If you only use the 1070 for rendering though, it will use all the RAM on that card. And it will render when you use both, but if you exceed the 6Gb of Ram on the 980ti, it will start using out of core operations which slow down performance.

edit: Man, that felt like a really clunky paragraph… xD Sorry, but English is not my native language…

This is a response I’ve been looking for thanks. So I can add another gtx nvidia card without sli as my board doesn’t support sli but I’m best of getting a card of similar performance. What about AMD? Is crossfire any good or would 2x non crossfire vega 56 be better?

I’m not familiar with AMD, so I really can’t give an advice there. It doesn’t matter really if it’s either crossfire or SLI, since blender doesn’t really utilize that type of function while rendering anyways. When it comes to rendering i’ve even seen clever people coming up with solutions that makes it possible to render with mixed cards as well… (I don’t know how stable that is though.) I would probably stay just with one brand, so Either Nvidia or AMD. In any case i believe it’s possible to use for instance an Nvidia card for the viewport, and use AMD’s cards for rendering (in cycles).
I guess the upside with AMD is that you get near gtx performance plus more ram for less money.

I kinda end up with Nvidia all the time though… I don’t really know why, but i guess it is something with buying new expensive things and the fear of getting less for the money. xD I have two 980ti’s…

AMD wise, I see no difference between crossfire on or off. Blender sees the two devices independently in OpenCL, as such treats them just fine.

I’ll do more testing, but so far no performance difference in Cycles