RAM bottleneck with RT?

[MANUEL_MOUSIOL]

I am thinking about getting a GTX 1080 ti additionally to my Quadro K4200 and GTX 1070, but I heard that I cannot use the 11gb in the 1080 ti because the bottleneck would be the GPU with the smallest RAM (which would be 4 or 8gb with my cards).
Couldnt find anything in the documentation and would like to have some clarification.
Thank you very much!

[savage309]

If you use multiple GPUs for rendering at the same time, you will be limited by the smallest amount of memory that each GPU has.

Best,
Blago.

[MANUEL_MOUSIOL]

so that means if I use all three of my cards vray only has 4gb or VRAM in total to use?

[savage309]

so that means if I use all three of my cards vray only has 4gb or VRAM in total to use?

Yes. Probably it is a good idea to use the Quadro for display only.

Best,
Blago.

[MANUEL_MOUSIOL]

Yes. Probably it is a good idea to use the Quadro for display only.

Best,
Blago.

ok, thank you.

I was wondering why that limitation exists? is it a thing that one day you can go around or is it hardware or driver related?

[savage309]

ok, thank you.

I was wondering why that limitation exists? is it a thing that one day you can go around or is it hardware or driver related?

Each GPU is a small computer, with processor, memory and so on. The chip needs ot access the memory as fast as it can (these days the memory is the bottleneck of the performance almost all the time). So, we make a copy of the data on each GPU.

NVLINK is hardware, that allows for fast comunication between GPUs, therefore it allows of stacking the GPUs memory (so if you have two GPUs with 16GB each for example, this makes something close to 32GB). It is very new technology (so still a bit pricy), but we already fully support it in V-Ray GPU. Available currently in the Quadro GP100.

Best,
Blago.

[MANUEL_MOUSIOL]

sounds good. just ordered two of them - lets get cracking!!

kiddin!

As always, I am so amazed about the repsonse time and the detailed answer here from you guys! Awesome customer relations! Thanks for the explanation! I hope that nvlink thing becomes a new standard for the cheaper cards too.

[JabbaTheNut]

What if I have two computers:
Computer 1) One GTX 1080 8GB
Computer 2) Two GTX 1080Ti 11GB

If I do V-Ray RT with distributed rendering, will I be limited to 8GB for both computers? Or, will I get 8GB on Computer 1 and 11GB on Computer 2?

[savage309]

What if I have two computers:
Computer 1) One GTX 1080 8GB
Computer 2) Two GTX 1080Ti 11GB

If I do V-Ray RT with distributed rendering, will I be limited to 8GB for both computers? Or, will I get 8GB on Computer 1 and 11GB on Computer 2?

When using distributed rendering, each node needs to have the whole scene. So you will be limited by that 8GB.

Best.
Blago.

[JabbaTheNut]

Bummer. Thanks Blago.

[JabbaTheNut]

Follow-up question...

I have a single computer with three graphic cards. They are as follows:

a) One Quadro K4200 4GB
b) Two GTX 1080Ti 11GB

If I select only the Two GTX 1080Ti 11GB graphics cards for use with V-Ray RT and use the Quadro K4200 4GB for my monitor an user interface only, will I get the full 11GB of the GTX 1080Ti's with V-Ray RT? Or will I still be limited to the 4GB of the Quadro K4200?

[savage309]

If you don't use the Quadro for rendering and render with the 1080ti only, you will be able to use the whole 11GB of the 1080ti.

Best,
Blago.

[JabbaTheNut]

Awesome! Thanks again Blago