Question Asus Pro WS W680-ACE: gen3 x16 card in PCIe 5.0 x16 slot that's bifurcated to 5.0 x8: possible?

JossBrown

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Jun 29, 2023
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Among other boards for a server/NAS build, I have my eyes on the Asus Pro WS W680-ACE workstation mainboard:

It comes with two PCIe 5.0 x16 slots (CPU). The board is for 12th & 13th gen Intel Core processors, which have 16+4 PCIe lanes, so you can either use one slot with gen5 x16 or both with gen5 x8 (manually or auto-bifurcated in BIOS).

However, I want to use two slower cards: a 10Gtek 710-25G-2S-X8 dual 25GbE SFP28 card, and a HighPoint Rocket 1104 quad M.2 NVMe card. The former is PCIe 4.0, the second one PCIe 3.0.

NIC

AIC

So I guess that I could go into the BIOS, and change the link speeds: one PCIe 5.0 x16 to gen4 link speed (network card), and the other 5.0 x16 to gen3 link speed (M.2 card).

The network card is x8 physical, which would be fine even with bifurcation. But a problem—and I'm pretty sure it's a problem—might be that the quad M.2 card is x16 physical & electrical, so it needs all 16 lanes, even if only at gen3 speeds. So my question is: would the board still bifurcate to 2x8 electrically, independent of the link speed setting in BIOS? Or are these systems intelligent enough to see that the overall PCIe bandwidth is low enough for the system to handle both cards without bifurcation?

In other words: would this setup work? Pro WS W680-ACE + 10Gtek 710-25G-2S-X8 (gen4 x8 in gen5 x16) + HighPoint Rocket 1104 (gen3 x16 in gen5 x16)?

From what I could gather online, if a card needs 16 lanes, it will need all 16 lanes, independent of link speed, and if it only got 8 in a bifurcated setting, it would run with half bandwidth/speed.

So if this setup doesn't work: are there quad M.2 NVMe cards using PCIe 5.0 x4 or PCIe 4.0 x8, which like the HighPoint device have their own controllers, so they would work without bifurcation?

Or maybe there are PCIe converters, i.e. to gen3 x16 from either gen4 x8 or from gen5 x4?

I hope that I have understood it all correctly. (Still new to this.) Thank you in advance for your input.
 
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Addendum – maybe a possible workaround: instead of the Rocket 1104, I could buy the (more expensive) HighPoint Rocket 1504 quad M.2 NVMe. This one is PCIe 4.0 x16, and with bifurcated lanes on the board (see above), it would only receive x8 speed/bandwidth at gen4 from the slot, but that would effectively be equal to x16 at gen3, which would be fine for me, because I only want to use gen3 M.2 NVMes anyway.

Woud this work instead? (I guess I'd have to contact the manufacturer anyway to be absolutely sure. Their cards use a special switch chipset, and I don't know how they behave when they only receive 8 instead of 16 lanes from the board.)
 
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