PCIE4 @ x8 mode for 2nd GPU?

[hrsetrdr]

I'm looking to double up my FAH GPUs, 2 in one rig. My X79 board has: 3 x PCI Express 3.0 x16 slots (PCIE1 @ x16 mode; PCIE3 @ x16 mode; PCIE4 @ x8 mode).
Will the PCIE4 @ x8 mode affect PPD for the GPU installed there?

[MeeLee]

I'm looking to double up my FAH GPUs, 2 in one rig. My X79 board has: 3 x PCI Express 3.0 x16 slots (PCIE1 @ x16 mode; PCIE3 @ x16 mode; PCIE4 @ x8 mode).
Will the PCIE4 @ x8 mode affect PPD for the GPU installed there?

It will. However, very minor.
Most GPUs will see a degradation at PCIE 3.0 x4, but PCIE 3.0 x8 usually runs fine (without much PPD loss; PCIE 3.0 x8 is about as fast as PCIE 4.0 x4).

So long your GPU accepts the PCIE 4.0 standard, you'll have to get something faster than an RTX 3090, to be bottlenecked by the PCIE 4.0 x8 bandwidth.

[bikeaddict]

Since PCIE4 @ x8 has the same throughput as PCIE3 @ x16 (what my machines and many other folders use) it shouldn't limit the speed at all. My NVIDIA Setting app shows I'm using 1% bandwidth.

[kiore]

Since PCIE4 @ x8 has the same throughput as PCIE3 @ x16 (what my machines and many other folders use) it shouldn't limit the speed at all. My NVIDIA Setting app shows I'm using 1% bandwidth.

Thanks for this, was wondering if this would be the case, my experience even on PCIE 3 at 8 the difference is noticeable but not huge, I think it those populating PCIE 3 x2 slots that were used for mining that suddenly see this critical drop.

[hrsetrdr]

I'm looking to double up my FAH GPUs, 2 in one rig. My X79 board has: 3 x PCI Express 3.0 x16 slots (PCIE1 @ x16 mode; PCIE3 @ x16 mode; PCIE4 @ x8 mode).
Will the PCIE4 @ x8 mode affect PPD for the GPU installed there?

It will. However, very minor.
Most GPUs will see a degradation at PCIE 3.0 x4, but PCIE 3.0 x8 usually runs fine (without much PPD loss; PCIE 3.0 x8 is about as fast as PCIE 4.0 x4).

So long your GPU accepts the PCIE 4.0 standard, you'll have to get something faster than an RTX 3090, to be bottlenecked by the PCIE 4.0 x8 bandwidth.

Since PCIE4 @ x8 has the same throughput as PCIE3 @ x16 (what my machines and many other folders use) it shouldn't limit the speed at all. My NVIDIA Setting app shows I'm using 1% bandwidth.

OK, thanks for defining this, if there were to be a significant impact on performance I would then have opted to run the GPUs in separate machines.

[Neil-B]

The biggest issue you may have is the thermal impact ... with two gpus in case the chances are the air flow will be impacted ... one or both gpus may potentially have thermal issues - either running hot or even getting to the point of thermally throttling.

Good airflow case with lots of fans and relatively low ambient temps you shouldn't have any issues but worth monitoring ... Cluttered case with minimal fans and you may have sub-optimal experiences.

[gunnarre]

Yes, so physical spacing between the slots you're going to use on the motherboard may be important too. Even in a good case, if the cards are sandwiched together with millimeter clearance, they may be thermally throttled.

[hrsetrdr]

The biggest issue you may have is the thermal impact ... with two gpus in case the chances are the air flow will be impacted ... one or both gpus may potentially have thermal issues - either running hot or even getting to the point of thermally throttling.

Good airflow case with lots of fans and relatively low ambient temps you shouldn't have any issues but worth monitoring ... Cluttered case with minimal fans and you may have sub-optimal experiences.

I was concerned, even-though my new build has all kinds of air flow the case is a mid-tower, and I'm thinking two fire breathing GPUs running 24/7 would cause an excessive heat build-up all around. So, whenever my new PSU gets here I've decided to put the RTX 3060 in with my GTX 1080, which is housed in a roomier server case.

[MeeLee]

The biggest issue you may have is the thermal impact ... with two gpus in case the chances are the air flow will be impacted ... one or both gpus may potentially have thermal issues - either running hot or even getting to the point of thermally throttling.

Good airflow case with lots of fans and relatively low ambient temps you shouldn't have any issues but worth monitoring ... Cluttered case with minimal fans and you may have sub-optimal experiences.

A good option is to get a high quality, 1 or 2 inch riser, that will allow the GPU to be mechanically mounted in a slot above or below the standard slot.

[hrsetrdr]

The biggest issue you may have is the thermal impact ... with two gpus in case the chances are the air flow will be impacted ... one or both gpus may potentially have thermal issues - either running hot or even getting to the point of thermally throttling.

Good airflow case with lots of fans and relatively low ambient temps you shouldn't have any issues but worth monitoring ... Cluttered case with minimal fans and you may have sub-optimal experiences.

A good option is to get a high quality, 1 or 2 inch riser, that will allow the GPU to be mechanically mounted in a slot above or below the standard slot.

Thanks, addressing the thermal issues is my current undertaking.