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Dual Video Cards... NVLink or not?

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  • PerttiAPerttiA Posts: 10,024

    Quite a few systems and GPU combinations in the Benchmark thread;

    https://www.daz3d.com/forums/discussion/341041/daz-studio-iray-rendering-hardware-benchmarking/p1
     

  • crosswindcrosswind Posts: 6,987

    jngzsz_adafce769a said:

    Thank you very much, you have clarified my doubts.

    I understand that the biggest benefit of having multiple cards lies mainly in the increase in rendering speed, and NVlink is not necessary.

    So, if I add another 4090 (which does not implement NVlink), would it increase the rendering speed?

    Tell me if I'm wrong.

    That's correct. With two 4090, Cuda cores will be doubled, the rendering time of  the same scene will be shortened by appr. 50%, as long as both cards are fully loaded for rendering.

  • franky85franky85 Posts: 133
    edited May 30

    jngzsz_adafce769a said:

    Thank you very much, you have clarified my doubts.

    I understand that the biggest benefit of having multiple cards lies mainly in the increase in rendering speed, and NVlink is not necessary.

    So, if I add another 4090 (which does not implement NVlink), would it increase the rendering speed?

    Tell me if I'm wrong.

    Yeah no need for nvlink for daz. One of my computers has two 2080TIs and NVlink/SLI made it.. worse.
    Also, for daz to use both GPUs properly I had to disable "Hardware-accelerated GPU scheduling" in the System --> Display --> Graphics --> Default graphic settings.

    Turning that off also brings back the CUDA section in the task manager's GPU pane, instead of having everything bunched up as "3D"

    Post edited by franky85 on
  • ZoritaeZoritae Posts: 26

    Ok.  I have already ordered the purchase of another 4090 plus a power supply for it.
    When it arrives and installs it, I'll tell you.
    Thanks and regards.

  • ZoritaeZoritae Posts: 26

    Hello again.

    I'm having a technical problem and I don't know if this is the right place to ask about it.

    I just received the second 4090. I installed it and everything seems to work, but neither the BIOS, nor Windows, nor GPU-Z, not even the Nvida panel recognizes the second card.

    Is it because the board does not have SLI-Nvlink support?

  • Richard HaseltineRichard Haseltine Posts: 100,948

    What do you mean by "everything seems to work"? One obvious test is to see if it works in place of the main GPU, on its own.

  • ZoritaeZoritae Posts: 26

    Hello.
    I already discovered where the problem is.
    I am using two power supplies of 1,000w each.
    I use one source for the plate, etc., plus the first GPU.
    The other, only for the second GPU.
    Well, the supply that only powers the second GPU does not work.
    I exchange them in case it is broken, and no, it is not broken.
    I get the feeling that these power supplies (Gold series) if they do not receive a signal that is powering the board, being prepared to be disabled in case of failure, they simply turn off and it does not work.
    I now have everything connected to a single source and now both cards are visible.

  • Richard HaseltineRichard Haseltine Posts: 100,948

    jngzsz_adafce769a said:

    Hello.
    I already discovered where the problem is.
    I am using two power supplies of 1,000w each.
    I use one source for the plate, etc., plus the first GPU.
    The other, only for the second GPU.
    Well, the supply that only powers the second GPU does not work.
    I exchange them in case it is broken, and no, it is not broken.
    I get the feeling that these power supplies (Gold series) if they do not receive a signal that is powering the board, being prepared to be disabled in case of failure, they simply turn off and it does not work.
    I now have everything connected to a single source and now both cards are visible.

    ATX power supplies, as far as I know, require the lines to/from the power switch to connect to trigger a start and those do pass through the motherboard on the way to the case switch. There probably are workarounds since people do use mutliple PSUs, but if you need that much power a bigger PSU would probably be wise.

  • ZoritaeZoritae Posts: 26

    Hello.
    Thanks for the information.   That has to be the reason.  I'll investigate how to trick the power supply.
    A 2,0000w power supply, here where I live, is around 500 euros.   A power supply of 1,000 can be found for 100€.   I'm talking about Gold Plus certified fonts.
    In the end, I connected a single source (1,000w) with the two cards.  I did render tests without seeing that the font was at the limit.   

    Render times have been shortened by just under 50%.  Which is a lot and worth the investment.
    Thank you and greetings.

  • Richard HaseltineRichard Haseltine Posts: 100,948

    Are you sure you need more than (or at least, as much as double) 1000W? 4090s are not as hungry as the previous generation, though I have no experience with them myself.

  • ZoritaeZoritae Posts: 26

    Hello.
    Well, I hear everywhere that a 4090 needs up to 850w at peak compute.   Actually, it has always seemed like an exaggeration, but it is what I read and hear everywhere.
    The truth is that when running GPU-Z while rendering, the consumption of the two cards does not exceed 240w each, and a maximum consumption of 65% TDP.   Therefore, there are indications to think that you are right.

    Anyway, I already got the information I wanted.
    It is true that the power supply, if it is not connected to the motherboard, does not turn on, but there are many people on Youtube teaching how to do it.   You just have to bridge two pins of the connector that go to the board and it turns on.  It's very easy.
    And I like that configuration, because in case I don't need to render, I can physically turn off a card and be left with only one, with all the advantages that that entails.

    As you can see, little by little I am learning.   Slowly, yes, but with joy.  XD

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