Interesting idea. It should work, right? Isn’t that what the low cost NVMe carrier boards do, routing 4 lanes to each m.2 without using a switch chip.
There are much less expensive risers on eBay, might be worth a gamble of you really need more slots.
Also could use simple extension cables to make use of slots that are covered by a large card.
My x399 has two full x16, two full x8 wired to the CPU, along with three x4 via m.2 slots.
I think it has two or three more slots that are not so fully wired but have the full size x16 connector. My 10g card is connected to one of the promontory slots, and is still wicked fast, faster than any network storage I have available.
That is exactly what those boards do! They just do it in a single slot package since the nvme size allows it.
The problem is that most ebay risers are 90 degrees risers, meaning that they face down once you plug them in and I don’t have the space for that. They might also be proprietary since many server OEMs use proprietary slots(?) and risers.
My X399 Taichi has 2x 16 and 2x 8 slots and 1 or 2 PCIe 2.0 x1(?) slots wired through the chipset. Unfortunately I don’t have an onboard 10Gb NIC but that is OK since I am using SFP+ gear anyway.
I did email a company that produces some x4 splitters to see if they are interested in making something that could be of use for X399 and normal tower computer cases.
It is a shame really that all companies that produce X399 did not add more PCIe slots, since you can bifurcate them manually, something that lower tier boards do by default (e.g. one x16 slot or 2x x8 slots on 115x Intel boards).
I feel a vertical GPU bracket could be modified to hold a larger riser easily enough. Many have room for 3 or even 4 slot GPUs to mount, so, two single slot cards should fit ok. You still need a chassis that supports such a thing. Use the x16 extender that comes with the kit to connect the splitter riser to the motherboard.
From just following the traces on that circuit board, it looks like the first x8 lanes go to the bottom slot and the next x8 lanes go to the top slot. A cheaper version is available without power injection.
PCIe 2 and 3 are electrically identical if I recall correctly, so it shouldn’t matter that it’s listed as gen 2 device.
My x399 Designare is similar, 2x16, 2x8 and 1x4 pcie 2.0 attached to the chipset. I confirmed, all three m.2 slots are pcie 3.0 and x4 bandwidth to the cpu. That checks out math-wise, 32 + 16 + 12 = 60, and the remaining 4 lanes connect the cpu to the chipset.
Taking the second x8 slot and splitting it x4 x4 would be plenty of bandwidth for a network controller, and something like an ssd, capture card or thunderbolt 3 adapter.
i remember i used one on a old fm2+ i ordered from a china company i can no longer find… most of them take a x16 slot and break it down is now usually in external boxes like how ltt did theirs a while ago
Yeah but something like this is bulky and requires case modding whereas you could adapt one motherboard PCIe slot and 2-4 “case slots” to 2-4 half height slots with the right PCB or some sort of riser cable (which would provide even more flexibility).
I know Wendell and EposVox were also complaining about the lack of more than 4 slots on HEDT platforms so they might hopefully be onto something!
Unfortunately this would occupy the whole slot where it is plugged in.
I have an X399 Taichi board in a Corsair 900D case. The motherboard has 4 PCIe slots to the CPU and 1 to the chipset (pretty useless for anything but USB controllers and soundcards).
Each motherboard slot corresponds to two on the chassis, apart from the bottom one.
If you have two 2-slot GPUs in slots 1 and 3, you are left with a two slot gap at slot 2 and in my case a 4 slot gap at the bottom slot (the 900D can accomodate up to 10 slots).
Slots 1 and 3 are x16 and slots 2 and 4 are x8 electrical. That means that with bifurcation you can split slots 1 and 3 to x8/x8 or x4/x4/x4/x4. Slots 2 and 4 can be split to x4/x4.
If you plug something like this in slot 2, you take up a slot and can only use the one underneath. There is no point in doing that.
If you plug it in slot 4, you can only double it so effectively you get 5 in total.
If you could produce this at a 90 degree angle and use half height cards, then you could use it at both slots 2 and 4 and end up with a total of 6. If you produced a flexible solution that can plug in slots 1 or 3, then you could multiply them 4 times. If they are flexible enough, you could use them with the bottom 4 unused chassis slots and could get up to the full 10 slots theoretically. It would also be usable in any computer case without mods.
90% or more of X399 motherboards use this layout, probably many of the X299 use something similar as well. Most 10Gb NICs and HBAs come with half height adaptors for server use.
MIning solutions are no good unfortunately. Devices like 10Gb network cards and HBAs need their PCIe 3.0 x4 bandwidth and the mining solutions only usually provide PCIe 2.0 or 1.1 x1.