GPU Bifurcation Question/Idea

[Kmpkt]

Wondering if anyone more knowledgable could comment on the viability of bifurcating one of these with a GPU:

https://www.asrock.com/mb/spec/product.asp?Model=ULTRA QUAD M.2 CARD

Considering there is virtually no performance loss using a GPU @ x8, would this quad M.2 be able to realize the full Raid-0 potential of say 4 x Samsung 960 Pro (14 GB/s) by using the other x8 of the PCIe slot?

 

[BryceK]

Where do you wanna use it on (which OS?) since at the moment the newer mobo's which use intel, only allow it when using Intel m.2 pci-e ssds and those don't go so high as the samsung onces.

 

[BryceK]

Asus also has such a card:

 

[Aki]

As far as I understand it, you would only be able to connect 2 additional M.2 drives, since the CPU would be running in x8 for the GPU and x4 x4 for this adapter on a mainstream CPU.

 

[Phuncz]

I guess ASRock would be your best bet at getting that answer, as they make this card and have a compatible board (Intel X299 or AMD X399 chipset) where you'd need Bifurcation. But since you're splitting the PCIe x16 port into two x8 ports, you're max bandwidth will be capped at half of the full x16.

 

[AleksandarK]

This could potentially work, but not at full speed. The M.2 drives are maxing out the bandwidth of the current PCIE gen 3 connector, unlike GPUs. That is why M.2 SSDs are going to have more benefit from going to PCIE 4 than GPUs.

The bandwidth of the the ASRocks adapter would be cut down to 8x, and given that the the board design is splitting the lanes into the four different connectors(4x when on 16x), they would operate at 2x and effectivly giving 50% speed reduction. Of course, this is just theoretical and it would need to be tested in order to have reliable information.

 

[EdZ]

New Wondering if anyone more knowledgable could comment on the viability of bifurcating one of these with a GPU:

How you can bifurcate with 'passive' risers depends on the capability of the device providing the slot. If you're looking to split a x16 slot with a GPU, I'll assume that'll be using lanes from the CPU rather than the PCH. For the majority of recent Intel* CPUs, this can be set as: x16, x8/x8, or x8/x4/x4 (maximums, so you could do x8/x2 or x8/x1 if you wanted). As @Aki says you cannot, for example, do x8/x2/x2/x2/x2.

(from the 8th Gen datasheet, but it's been effectively unchanged for several generations)

What I do not know, and what probably has not really been tested by anyone, is whether you could take one of these quad m.2 cards and use it as 'just' a dual m.2 card (bifurcating x8 to two x4 slots).

*AMD do not appear to even bother publishing datasheets (or if they do, they're so well hidden in their awful website design nobody can actually find them), so the bifurcation capabilities of Ryzen is a big fat ¯\_(ツ)_/¯

 

[Kmpkt]

The other thing to consider here is when PCIe Gen 4 hits it will double all of this so these two would effectively function as 3.0 x16 each

 

[ChinStrap]

I asked that very question in the asrock x370/b350 gaming itx thread.

https://smallformfactor.net/forum/t...d-ab350-gaming-itx-ac.2341/page-19#post-80770

not much going on.

I also asked on the asrock forums: http://forum.asrock.com/forum_posts.asp?TID=7254&title=x370-gaming-itx-nvme-raid-0

thread highlight: "AMD says NVMe support should be available soon for X370, waiting on BIOS from board vendors. It should look very much like X399. Please open a ASRock ticket and see if you can get them going."

From what I have gathered, you need a board that can be set for Bifurcation level 4x/4x/4x/4x. Boards with only Bifurcation support for 8x/8x don't support the card. you also need platform support from the CPU & BIOS. So, who knows. Once the new APUs start showing up, I would love some NVMe raid 0 on my x370.

If you find anything else, please update.

Thinking about it a little, I can see AMD supporting it on future x470 products as a means to upgrade. That would be Lame.