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Rendering time with 2 cards vs 1

mikec0781mikec0781 Posts: 10
in Technical Help (nuts n bolts)

First off I know there are many posts already regarding running multiple cards and sli etc so I apologize if this is redundant but Im not seeing a clear answer anywhere to my question. 

I currently have one gtx1080 and im not concerned about fitting my scenes in 8gb that is plenty. What i want is to significantly reduce rendering time. I can grab a second 1080 refurbed for $400. Will it render significantly faster having two?

Comments

  • j1039564j1039564 Posts: 19
    edited October 2018

    Yes mode cuda cores will make your render go a lot faster. There are spreadsheets, search, you can see others performance with multiple GPUs.  You will only be able to use 8GB GPU memory though, it does not stack!

    Post edited by j1039564 on
  • ebergerlyebergerly Posts: 3,255

    Two 1080's will probably render a scene in about 60% the render time of one 1080. So a 10 minute render with one might be a 6 minute render with two. Or something like that. Not quite cutting render times in half, but close. 

    Oh, and you mention SLI. Don't use SLI with Iray (I assume you're talking Iray here). 

  • rames44rames44 Posts: 332

    Yup - I’m rendering with two 1080’s. Tried a few samples with one, and two give me a render time that runs between 52 and 60% of just one.  Depends on the scene.  My guess is that having the second card increases the amount of time spent loading up geometry and textures, but then runs pretty close to twice as fast once that’s over.  So for short rendering scenes, you don’t come as close to true 2x because of the load time. For long rendering scenes, I seem to get closer to 2x. Also, my monitor is running off one, so there’s some effect there.

    SLI won’t help, and may hurt, so make sure it’s turned off or just don’t get the connector. (My system came with one.)

  • KitsumoKitsumo Posts: 1,216
    edited October 2018

    I never noticed longer load times with multiple cards. Even when I lowered PCI-E slots to 1x the load times did increase but only by a second or two. What kind of times are you seeing rames44? (after you close or save a render, the log file shows the load and render time for each card) I'm just curious as to what other people are getting.

    Post edited by Kitsumo on
  • MattymanxMattymanx Posts: 6,955

    Nvidia's own documentation on Iray states to disable SLI before rendering in Iray.

     

  • Taco DestroyerTaco Destroyer Posts: 10

    using 2 cards has been the biggest performance boost with i ray! even intermediate open gl flies! i use a 1060 in combo with a 750 ti and its a night and day difference. ive tried new processors, software plugings, even overclocking nothing comes close to mutiple nvidia cards. imagine 3 cards. whoa lol

  • rames44rames44 Posts: 332
    Kitsumo said:

    I never noticed longer load times with multiple cards. Even when I lowered PCI-E slots to 1x the load times did increase but only by a second or two. What kind of times are you seeing rames44? (after you close or save a render, the log file shows the load and render time for each card) I'm just curious as to what other people are getting.

    Been a long time since I ran the experiments, and I don’t recall if I actually looked at the load times in details - I may have just assumed that that was the reason for what I was seeing time-wise.  Might have to go back and repeat with the magnifying glass on the times in the log file. 

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