To date, we have looked at a total of three NVIDIA GeForce RTX 3090 graphics cards, the NVIDIA RTX 3090 FE, ASUS ROG Strix RTX 3090 OC, and ZOTAC RTX 3090 Trinity. All three GPUs are extremely capable graphics cards by themselves. At the time of this review, we had two RTX 3090 GPUs here in the lab and wondered what type of performance numbers we might generate using an SLI/ NVLink multi-GPU configuration.
NVIDIA GeForce RTX 3000 series graphics cards are somewhat of a problem. NVIDIA has basically dropped SLI support with the RTX 3000 series graphics cards. Not only does NVIDIA drop support, but most of the graphics cards themselves do not come equipped with the ability to use an SLI or NVLink bridge. NVIDIA has been slowly phasing out the consumer edge connector for this. However, one card in the lineup includes a NVLink edge connector, the RTX 3090.
The latest NVIDIA drivers for the 3000 series of graphics cards will not show SLI options even if one has the NVLink bridge installed. When one opens up the NVIDIA Control Panel and drills down into Manage 3D settings/ Program Settings, the traditional SLI settings are not there with an NVLink bridge in place.
This phasing-out of SLI in favor of NVLink on higher-end GPUs makes a lot of sense. There is such a large delta between low-end GPUs and high-end data center GPUs that one can often scale in a single GPU system. Still, with NVIDIA seemingly phasing out SLI, we are no longer in the days that one can get two smaller cards for less than a larger card and get a value SLI setup. For our purposes, on the compute side we found that programs that can use multiple GPUs will result in stunning performance results that might very well make the added expense of using two NVIDIA 3000 series GPUs worth the effort.
We started off going down the multi-GPU adventure with two RTX 3090 graphics cards, the ASUS ROG Strix RTX 3090 OC and ZOTAC RTX 3090 Trinity. We did have a few problems to overcome. First, the ASUS ROG Strix RTX 3090 OC is simply huge, much like a large brick. A keen observer would also spot the size difference between the two cards hights. The ASUS ROG Strix RTX 3090 OC is 5.51″ tall, while the ZOTAC RTX 3090 Trinity is 4.75″ tall. We found our SLI bridge would not line up as the ZOTAC card was much lower. Being creative and only planning on running this configuration for these benchmarks, we ordered a PCIe x16 Extender Riser cable to lift the ZOTAC card. We now had a fully SLI configured system.
Clearly, this was not an optimal configuration to run long term, but it did serve for running our benchmarks.
We are also going to quickly note that even as GPU prices have drifted upward, GPU-to-GPU connectors have gone from free items in motherboard boxes to $75+ parts.
The last item to note. Being able to purchase even a single RTX 3090 is next to impossible unless you head down the second-hand market. Then getting two of the same RTX 3090 graphics is even more difficult. Normally we would want to run two NVIDIA RTX 3090’s that are the same, however, we have to recognize that is not the environment we are in. The prospect of having two different cards is simply a sign of the times. If this was a week or two where availability was tight, then we would understand. Instead, this has been a persistent challenge since the cards launched spanning many quarters.
We figured it might be worth the experiment to run our two RTX 3090 graphics cards in an NVLink configuration and see what we might get in our benchmarks. We can then gauge whether going down the multi-GPU (desktop compute) route is even worth it in the first place. For many use cases, the power and cooling requirements will make this impractical to have on the desktop. Having more than two GPUs in a desktop system these days is possible, but the practical aspect will force multi-GPU workloads to data centers and data cabinets.
The market has changed since we did our dual NVIDIA Titan RTX NVLink and dual NVIDIA Quadro RTX 8000 NVLink reviews. Part of that is due to NVIDIA’s product lineup while some change is simply due to market conditions.