PCI-E Bifurcation

LukeD

Master of Cramming
Case Designer
Jun 29, 2016
427
1,153
I used the Amerirack riser. And then used LiHeat risers with that :)



Here are the FireStrike results:



What i did was inject the SLI certificate using DSDT. Its not a walk in the park, but it can be done and then SLI works without issues. You can see the FireStrike result validated which says SLI: ON :)
 

Biowarejak

Maker of Awesome | User 1615
Silver Supporter
Mar 6, 2017
1,731
2,218
Been meaning to design my own, got everything pinned out in Eagle, just haven't been bothered to study the PCIE spec and how it ties into the bifurcation chip.
 
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aquelito

King of Cable Management
Piccolo PC
Feb 16, 2016
887
995
Did you make any progress ?

I designed a custom enclosure around my dual-slot riser.
Looks way cleaner than the Amerirack one, while I trust good old PCB traces rather than a PCIe ribbon to feed my two 1070s with 12V.
Works like a charm :)

Some close up preview picture ; I'll do a proper thread later on.

 
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Biowarejak

Maker of Awesome | User 1615
Silver Supporter
Mar 6, 2017
1,731
2,218
Did you make any progress ?

I designed a custom enclosure around my dual-slot riser.
Looks way cleaner than the Amerirack one, while I trust good old PCB traces rather than a PCIe ribbon to feed my two 1070s with 12V.
Works like a charm :)

Some close up preview picture ; I'll do a proper thread later on.

Looks awesome! No progress on the riser yet; I've been juggling a few other things. I really need to structure my time more effectively so that I can get back on it.
 

aquelito

King of Cable Management
Piccolo PC
Feb 16, 2016
887
995
Question regarding the STRIX Z370-I Gaming :

this mobo is supporting Bifurcation through their Hyper M.2 X16 card, which can carry up to four M.2 drives.
Manual specifies two possible PCIe configurations :

- two drives : x4 + x4
- tthree drives : x4 + x4 + x4

Any chance the PCIe slot could be configured in x8 + x8 ?

@1461748123 ?
 

1461748123

Master of Cramming
Nov 5, 2016
489
1,065
Question regarding the STRIX Z370-I Gaming :

this mobo is supporting Bifurcation through their Hyper M.2 X16 card, which can carry up to four M.2 drives.
Manual specifies two possible PCIe configurations :

- two drives : x4 + x4
- tthree drives : x4 + x4 + x4

Any chance the PCIe slot could be configured in x8 + x8 ?

@1461748123 ?
Not an expert in this area, sorry man :(
 

gunpalcyril

Airflow Optimizer
Aug 7, 2016
287
310
Been scouring around to confirm this, if anyone can verify for me that would be greatly appreciated.

Does the asrock b350 itx motherboard have bifurcation support for dual gpus (2 x 1070's)? Or does this only work on the x370 version?
 
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jtd871

SFF Guru
Jun 22, 2015
1,167
845
Been scouring around to confirm this, if anyone can verify for me that would be greatly appreciated.

Does the asrock b350 itx motherboard have bifurcation support for dual gpus (2 x 1070's)? Or does this only work on the x370 version?
Contact AsRock pre-sales support and straight-up ask?
 

RavenIII

Minimal Tinkerer
Jan 26, 2017
4
1
AsRock Fatal1ty X470 Gaming-ITX/ac have unlocked bifurcation but Asus ROG Strix X470-I Gaming have it lock
From what I can understand by myself and after plenty hours of research, is it because Asus motherboard use a second M.2 slot for NVMe?
AsRock can use all 24 lanes at once. PCI-E 3.0 x16 (16 lanes), USB 3.1 Gen2 (4 lanes) and M.2 (4 lanes)
Asus have one M.2 NVMe/Sata port more so it is 4 extra lanes of use. When you have connected 2 M.2 NVMe SSD's your device on x16 slot is working in x8 mode (if i correctly understand my native language)

So, if x16 slot is working in x8 mode when you connect 2 NVMe drives, is it not a bifurcation? Correct me if I'm wrong. Can not we bifurcate x8 to 2 x4? If we install 1 NVMe drive or none of them, aren't we possible to bifurcate x16 to 2 x8? It's a silly move Asus...

(sorry if it stupid but I'm newbie in bifurcation)
 

Aki

Average Stuffer
Aug 9, 2016
83
82


Using an Asus x470i with a m.2 to PCI-e riser on the slot on the bottom of the Motherboard (inside a Sentry). It does not support bifurcation but at least you can do this and still have a nvme ssd.
 

zovc

King of Cable Management
Editorial Staff
Jan 5, 2017
852
601
So, my understanding of this is limited and I could be wrong, but here's my understanding.*

From what I can understand by myself and after plenty hours of research, is it because Asus motherboard use a second M.2 slot for NVMe?
AsRock can use all 24 lanes at once. PCI-E 3.0 x16 (16 lanes), USB 3.1 Gen2 (4 lanes) and M.2 (4 lanes)
Asus have one M.2 NVMe/Sata port more so it is 4 extra lanes of use. When you have connected 2 M.2 NVMe SSD's your device on x16 slot is working in x8 mode (if i correctly understand my native language)

So, if x16 slot is working in x8 mode when you connect 2 NVMe drives, is it not a bifurcation? Correct me if I'm wrong. Can not we bifurcate x8 to 2 x4? If we install 1 NVMe drive or none of them, aren't we possible to bifurcate x16 to 2 x8? It's a silly move Asus...

(sorry if it stupid but I'm newbie in bifurcation)
PCI-E works in groupings of lanes, x1, x2, x4, x8, and x16. (Maybe x32 and beyond is technically a thing, but it doesn't really matter here.)

When a motherboard manufacturer is designing a board/working with a chipset, it's up to them to engineer the lanes as they see fit. The engineering of the board will dictate where the lanes physically go. However, PCI-E as a protocol can only work in the above lane increments.

So, if a PCI-E slot had 24 lanes physically going to it, it still is only going to run at x16 at maximum--you wouldn't see an engineer design a board this way because it'd be using lots of resources for literally no gain.

In a more realistic use-case, let's say we have a PCI-E slot and a M.2 slot both going through the chipset. Our PCI-E slot, physically has, 16 lanes, and our M.2 slot has 4 physical lanes. In the case of X370, we can use 24 lanes at any given moment. This means our GPU can run at x16 and our M.2 drive can run at x4, and we're still only using 20 of our 24 PCI-E lanes.

Of course, things like our SATA ports or USB 3.1 Gen2, like you mentioned, are going to take up PCI-E lanes on our chipset, too. Maybe the board has a built in M.2 Wifi card (typical on Mini-ITX boards), whatever. These devices are generally going to take up between 1 and 4 PCI-E lanes. Which can lead to a weird situation.

Let's say we have an NVMe SSD running at PCI-E x4 in one of our M.2 slots, our motherboard's USB 3.1 Gen2 is built into the chipset and using PCI-E x4. We've also got a Wifi card built into the motherboard using PCI-E x1. We're using a total of 9 of our 24 PCI-E lanes--there's only 15 left.

It's not possible to run a device at PCI-E x15, and we don't have 16 lanes free anymore--if we run a GPU, it's going to run at PCI-E x8 or lower.

Long story short: our devices are sharing all of our available PCI-E lanes.

To answer your question "Is it not a bifurcation?"... I actually don't know the technical answer. But, when we refer to PCI Bifurcation, we're specifically referring to running two devices off of one physical slot. Whether or not a motherboard will support this depends mostly on how the logic/software of the board is designed. My understanding is it's basically as simple as the manufacturer "turning the feature on," but I have no perspective on what the development to achieve that is like.

The basic problem we run into is, as consumers, the hardware we're normally using is not designed to suit every possible use-case. Manufacturers and engineers spend a lot of time and effort trying to make their motherboards (etc) simple, plug-and-play, and "fool proof." This is usually a good thing, but it can sometimes mean that supporting something "niche" like PCI bifurcation never enters the conversation.
 

APSinc

Minimal Tinkerer
Jul 30, 2018
4
2
I'm curious; I was looking at the ASRock Fatality mITX motherboard and noticed that it supported Bifurcation which makes me wonder, is it possible to run something like a graphics card and a bootable NVMe SSD on a birfucating riser? Is the bifurcation limited to splitting the signal between similar data types, or is this more of a manufacturer/BIOS limitation than a physical limitation of the standard?

The ASRock Motherboard in question only has 1 NVMe slot, so the question is more of a hypothetical use case where I'd be combining an Optane accelerator drive for a standard HDD storage drive with a boot NVMe SSD on the PCI riser. It's an edge case for sure, but it's not really clear from what I've read if this kind of use has really been considered seriously, particularly since a lot of the results on Google go either back to this thread or to bifurcation riser cards rather than actual specs on the specific capabilities or use cases aside from SLI/Crossfire.
 
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zovc

King of Cable Management
Editorial Staff
Jan 5, 2017
852
601
Is the bifurcation limited to splitting the signal between similar data types, or is this more of a manufacturer/BIOS limitation than a physical limitation of the standard?
I am not qualified to give you a certain answer, so definitely keep looking if you want to have confidence... but my understanding is that if your board supports bifurcation it should not matter what the two devices you're using are. I don't know whether bifurcation is able to split into more than halves--x16 into x8+x8, or x8 into x4+X4, rather than x16 into x8+x4+x4, etc--but I don't see any reason why a GPU using x8 and a NVMe drive using the other half (I think they only use up to x4) should not work.

I could be mistaken, but I believe someone's used a GPU and a capture card off of the same slot via bifurcation. Maybe you could even use a GPU in x8 and a NVMe RAID card at x8, rocking two drives at x4 each?
 
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jtd871

SFF Guru
Jun 22, 2015
1,167
845
I'm curious; I was looking at the ASRock Fatality mITX motherboard and noticed that it supported Bifurcation which makes me wonder, is it possible to run something like a graphics card and a bootable NVMe SSD on a birfucating riser? Is the bifurcation limited to splitting the signal between similar data types, or is this more of a manufacturer/BIOS limitation than a physical limitation of the standard?

The ASRock Motherboard in question only has 1 NVMe slot, so the question is more of a hypothetical use case where I'd be combining an Optane accelerator drive for a standard HDD storage drive with a boot NVMe SSD on the PCI riser. It's an edge case for sure, but it's not really clear from what I've read if this kind of use has really been considered seriously, particularly since a lot of the results on Google go either back to this thread or to bifurcation riser cards rather than actual specs on the specific capabilities or use cases aside from SLI/Crossfire.
A bifurcating riser will split the PCIEx16 traces into x8/x8. AFAIK you can then theoretically run any* PCIE devices off those two slots as up to electrically x8 devices.

The motherboard needs the BIOS to explicitly support bifurcation to be able to "know" there are 2 devices running off the slot.

*Power limits may apply for slot-powered devices.
 

xSanchez78

Average Stuffer
Jan 15, 2018
57
56
Does the AsRock Fatal1ty X470 Gaming-ITX/ac have properly working PCIe bifurcation? I know the X370 does but I heard from the review of this motherboard that it doesn't work to well... could someone confirm?
 
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ChronoDog

What's an ITX?
Jan 29, 2018
1
2
I'm curious; I was looking at the ASRock Fatality mITX motherboard and noticed that it supported Bifurcation which makes me wonder, is it possible to run something like a graphics card and a bootable NVMe SSD on a birfucating riser? Is the bifurcation limited to splitting the signal between similar data types, or is this more of a manufacturer/BIOS limitation than a physical limitation of the standard?
Currently running a 1080Ti + NVMe 960Pro (as a boot drive) off of a bifurcated riser, I can confirm this works - but as stated above, it requires explicit BIOS support, an actual option you can toggle to turn it on or off.
 

amback

Minimal Tinkerer
Jan 12, 2019
3
0
Hi guys am new but been reading this thread is pretty interesting to say the least, i still need some directions. with the introduction of nvidia 20s series gpus they said that they don't officially support 4-way sli BUT am assuming that using this way(Bifurcation) we can bruteforce 4 gpus. 2 gpus in 2 x8 slots and 2 more gpus in 2 x8.

a few questions that i got are

1. If we take the 1 x16 and split it into 2 x8 and connect 2 2080ti, do we need to also connect an sli bridge?

2. Has anyone done this setup to do a 4-way sli with the latest 20s series gpus?

3. which latest amd or intel motherboard can i use use to support it, i heard lots asrock motherboards has support for it.
 
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