Dual RTX 3090

[Magu]

Hi there,

I recently switched from hackintosh to Windows getting an RTX 3090 (what a revolution ).
I'm now wondering if I can mount a second one in my current configuration :
- ASUS Z490-E GAMING motherboard
- Intel 10850K CPU with Be Quiet Dark Rock Pro 4
- MSI GeForce RTX 3090 GAMING TRIO
- Fractal Design Define 7 Compact case (ATX)
- Seasonic Prime TX 850W PSU (I know that I'll we have to switch to 1500W)

Do you think it's reasonnable to mount 2 RTX 3090 ? My main interrogations are about space / temperature.
The space between the 2 cards is certainly going to be very tight...
Thanks for your help.

 

[Alex Glawion]

The pcie-lanes on the expansion slots of the ASUS Z490-E GAMING will drop down to 2x x8 when using two GPUs. This could impact your performance, given that they are still pcie 3.0. It'll depend on your workloads if you see a considerable impact on performance when your bandwidth is throttled.

The MSI GeForce RTX 3090 GAMING TRIO of course also is an open-air cooled GPU that will not perform optimally in a multi-gpu stacked config, so expect some slowdowns because of temperature throttling here as well unless you have some really good case ventilation.

Everything considered, I'd say entirely possible, but you won't get the full potential ou of the GPUs.

 

[Magu]

Thanks a lot for the quick answer @Alex Glawion.
The Define 7 is highly configurable, so I think I can optimize ventilation adding fans and switching top and front panels (from closed to filters).

I've seen some posts talking about this x8 drop down but the real impact is not really clear. Sometimes talking about between 5% and 8%, sometimes between 50% and 100%, sometimes no performance drop down at all depending of scenes and / or vram...

However the good news is "Yes we can" .
I just didn't want to change now my whole configuration which is pretty recent. I'd still do it later if I notice a very annoying drop down.
2x 3090 on x8 PCI lanes will still be faster than one on x16 (at least I hope so)

 

[Magu]

Interesting article by Puget about PCI generations and 3D rendering : https://www.pugetsystems.com/labs/a...ne-Scaling-in-OctaneRender-and-Redshift-1259/

Obviously I work with Redshift

 

[Alex Glawion]

Jup, though that's with a 2080Ti that barely saturates x8 pcie3. For pcie4, these tests py Techpowerup are interesting, but unfortunately they only really test gaming: https://www.techpowerup.com/review/nvidia-geforce-rtx-3080-pci-express-scaling/27.html

 

[Magu]

According to Puget's moderator in this article, PCIe 4.0 8x is comparable to PCIe 3.0 16x : https://www.pugetsystems.com/labs/a...VIDIA-GeForce-RTX-3080-3090-Performance-1892/

He is also pointing this article : https://www.pugetsystems.com/labs/articles/PCI-Express-4-0-vs-3-0-Video-Card-Performance-1982/

The drop down is not that huge. I think I'll try.
If you want @Alex Glawion, and if you have a C4D / Redshift test scene, I can post here my before / after results.

 

[Alex Glawion]

You can do two runs if you have time for it. One with the redshift benchmark scene and another with a scene that has 50mio polys or more (just duplicate or subdivide a bunch of primitives). Thanks!

 

[Magu]

Well, I called my retailer and there is no 3090 available actually.
If I really want one, I've to wait and pay 3000€ for it (my first one was 2600€ 2 months ago).
Knowing I'll get a performance drop down, I refuse to pay so much for a card supposed to cost 1500$...

Finally I'll wait for the launch of the 3090ti and / or a better price.
Considering this shortage and speculation, I wonder if next Mac Pro could be an descent alternative since it will not be possible to mine with...

 

[Alex Glawion]

Yes GPUs are crazy expensive right now. I am waiting for prices to come down as well, as are a lot of people. Thumbs crossed.

 

[Magu]

Hi,

some news about my build.

I noticed that the 3090 was getting very hot (VRAM up to 106°C).
To fix it, I did the following :
- undervolted the card
- adjusted GPU's fans curve
- got a new case, the Fractal Design Torrent
This case is just amazing for air cooling. I don't want to switch to water cooling because it's quite complicated, needs regular maintenance, has a short lifespan compared to air cooling...
Doing that, the temperature dropped down to max 94°C.

Moreover I read that the expected performance of the 3090 ti will only be 10% better than the 3090. It is not worth the cost of replacing the 3090.
I therefore plan to get a second GPU : an RTX 3060.
This is the only 2 slots (I want to keep 1 free slots between the two GPUs for air flow) / 12Gb available card and one of best price / value card according to CG Director's benchmark. I'll run the 3090 as main GPU to let all applications use its VRAM. 3060's 12Gb will be available for Redshift rendering.

What do you think about this setup ?

 

[Alex Glawion]

You have an open-air cooled 3090, right? Then you'll definitely need a slot in between the two cards, yes.

The thing with very different GPUs for rendering, is, that the VRAM will be capped to the smaller amount of you render on an image with both GPUs. You'll have to render two tasks at once, each on one GPU, to make use of the full amount of VRAM.

You don't want the 12GB of VRAM bottleneck the 24GB on the 3090.

 

[carpetbomber]

Hi there, I stopped by to revive this older thread because I am considering the same combination - but I am not 100% everything will fit: two ZOLTAC 3090, in a Define 7 compact. Have you had the chance to finish the double?