“Dual” bifurcation?

[Weapon]

I have an Asrock C246 board and 2x Supermicro PCI-E to dual m.2 drive cards. I’m trying to use all 4 drives in the system but only the card/drives in the 16x slot (PCI-E 4) are detected. I’ve tried all possible BIOS settings but nothing changes. Any ideas?

Note there is an m.2 to u.2 converter in the photo but the drive isn’t actually powered on, I disconnected it, thinking that may be the issue but alas.

 

[zir_blazer]

Which adapters? Most likely you will not get them to work because you're using adapters that rely on platform supporting PCIe Bifurcation on one that doesn't.

 

[RolloZ170]

PCIe Slot6 and Slot4 chare 16 PCIe lanes from CPU.
the x16 Slot should be Slot6 not 4.
from the manual:
Expansion Slot
PCIe 3.0 x16 Slot 6:
Gen3 x16 link, auto switch to x8 link if Slot 4 is occupied
(Physical x16, EE x16/x8 (from CPU), shared with Slot 4)

PCIe 3.0 x8 Slot 4:
Gen3 x8 link (Physical x8, EE x0/x8 (from CPU), shared with Slot 6)

check if you can force the Slot6 x8 / Slot4 x8 bifurcation setting in the BIOS

 

[Weapon]

Which adapters? Most likely you will not get them to work because you're using adapters that rely on platform supporting PCIe Bifurcation on one that doesn't.

AOC-SLG3-2M2, why do you say the platform doesn’t support bifurcation?

 

[Weapon]

PCIe Slot6 and Slot4 chare 16 PCIe lanes from CPU.
the x16 Slot should be Slot6 not 4.
from the manual:
Expansion Slot
PCIe 3.0 x16 Slot 6:
Gen3 x16 link, auto switch to x8 link if Slot 4 is occupied
(Physical x16, EE x16/x8 (from CPU), shared with Slot 4)

PCIe 3.0 x8 Slot 4:
Gen3 x8 link (Physical x8, EE x0/x8 (from CPU), shared with Slot 6)

check if you can force the Slot6 x8 / Slot4 x8 bifurcation setting in the BIOS

Yes, 16x is slot 6, I typed that wrong. It has the option for 8x/8x but only card in slot 6 is detected

 

[Markess]

What options does it offer you for "PCIE6 Link Width" in the BIOS Advanced>Chipset Configuration Menu? There probably isn't a Link Width option for PCIE4 is there?

If its like most other C2xx Chipsets that have bifurcation exposed, you'll only be able to bifurcate one slot, and it will have "Auto", "X16", "X8X8", and "X8X4X4", or a subset of those to choose from. Maybe also CPU dependent since these are CPU PCIe lanes?

I've never seen a C2xx chipset board with an X4X4X4X4 option, which I'd assume is what you need to work with four x4 NVMe drives.

I think that, without an "X4X4X4X4" option, you're only going to get X4X4 on one slot, and maybe X8 on the other, so long as the motherboard 's PCIE auto switch to split lanes between slots isn't disabled by a selection other than "Auto" that is. I could also see the BIOS locking out the motherboard switch when bifurcation is selected, in which case you'd get bifurction on PCIE6 and PCIE4 would be "dead".

To get all 4 drives, I'd think that you'd need an X4X4X4X4 configuration that also works within the motherboard's auto X8 + X8 switch. Not sure anybody makes something like that?

EDIT: OTOH, if anyone does make a C2xx chipset board with X4X4X4X4 as an option, I hope other members who read this will please let us know. I'd think a number of folks might like to have that option.

 

[zir_blazer]

EDIT: OTOH, if anyone does make a C2xx chipset board with X4X4X4X4 as an option, please let us know. I'd think a number of folks might like to have that option.

That is impossible. The PCIe Controller of the Processor only supports 16x, 8x/8x and 8x/4x/4x modes.

 

[Markess]

That is impossible. The PCIe Controller of the Processor only supports 16x, 8x/8x and 8x/4x/4x modes.

I thought so, but being a member here I’ve learned that what I don’t know exceeds what I do know by several orders of magnitude!

 

[Weapon]

So after some experimenting, as I now understand from the description of the bifurcation modes, the board behaves pretty much as expected.

If set to auto or 8x/8x only one m.2 SSD in each adapter card is detected in PCIE 4 and 6

If set to 8x/4x/4x, then one m.2 in PCIE6 is detected and both in PCIE4

I am able to put the 4th m.2 SSD in the motherboard slot and it is detected so overall it works but the dual m.2 card is wasted so I will probably look for a single card converter.