X299 motherboard choices

[kylec]

I've built a few X299 systems, now, and I thought I'd share some observations about the motherboards that are available.

To my mind, the best way to break down X299 motherboards is by the way that they handle routing of PCI-e lanes. Having 44 (or with Cascade Lake-X, 48) CPU lanes is the big advantage with this platform, compared to the standard desktop CPUs that still only have 16 CPU-connected lanes. So here's what that breakdown looks like:

• boards that don't route all available CPU lanes to the expansion slots: this includes most of the ASUS boards, most of the Gigabyte boards, and the cheapest option from some of the other brands. Usually one of the M.2 slots is CPU-connected, but there still may not be a way to use all available lanes, so this is not so desirable.
• boards that do route all CPU lanes to the expansion slots; the onboard M.2 is either PCH-connected, or has the option of using CPU lanes but at the cost of losing a slot. There is a very cost effective option in this category: the MSI X299 Pro at only $250. If not using Cascade Lake, the ASUS Prime X299 Deluxe is also in this category (it will be x16/x4/x16/x8 instead of x16/x8/x16/x8).
• boards that route all CPU lanes to the expansion slots, but switch x8 down to x4 when an M.2 is installed: this is quite handy! Includes the ASRock X299 Taichi CLX, which is x16/x4/x16/x8 when a single M.2 is installed in the correct slot. If you're using a Thunderbolt AIC, there needs to be one x4 slot in order to not waste lanes.
• boards that use PCI-e switches to provide more expansion slot bandwidth than is available on the CPU: Gigabyte X299-WU8, ASUS WS X299 SAGE, etc. They're quite expensive, and to me it's probably only worth it if the system has 4 GPUs.

I also want to share one more thing that I've just figured out, which I think is a pretty cool hardware hack! The price difference between the MSI X299 Pro and the ASRock X299 Taichi CLX is at least $150. But the MSI board can bifurcate that last PCI-e slot (or any of them, actually). If you get a case that has the two additional expansion slots that mount vertically (my favorite is the Corsair 275R Airflow), then we can use this to upgrade the MSI board to x16/x8/x16/x4/x4! You will need an adapter board and two cables. For the board, we'll use this:

Supermicro AOC-SLG3-2M2 dual x4 M.2 to PCI-e x8 - https://www.amazon.com/dp/B071S3ZY8P/?tag=tonymacx86com-20

And then for the extension cables:

M.2 M-key to PCI-e x4 extension R42SF 15cm - https://www.ebay.com/itm/223574412310?var=522319592980

The BIOS setting is in the menu for "VROC settings," or something like that. You just enable bifurcation on PCIE4, which splits the last x8 slot to x4/x4.

I also tried doing this the other way, with a bifurcation adapter card from Supermicro and then a regular PCI-e riser cable. The problem is that with the available bifurcation adapter, it doesn't quite fit in the case, and the riser cable doesn't line up straight, so it's not good that way. The M.2 based approach is only a little bit more expensive, and much better at keeping the cables intact and clear of your GPU.

Hope it's helpful to somebody!

 

[oli.mathieu]

nice to know
thanks

 

[hotbullet]

kylec are you able to have more than one nvme on vroc enable in OS X. I have asus card if I enable vroc OS X would not see even one nvme. If I disable vroc I can have one nvme visible in is Catalina. I am using as rock creator.

thanks

 

[kylec]

BIOSes seem to handle this in various different ways, so you might have to experiment with different combinations of settings. The best behaved will just locate all PCI-e devices and make them available. Some might only show the devices on bifurcated slots (which is kind of the subject of this post) after the master "RAID on" setting is turned on. That may be labeled VROC in your case. The same setting may also control SATA behavior, which is unfortunate. When this sort of thing happens to me, I always go into the hidden variables (accessible via IFR export), and usually there's a resolution.

The important thing, though, is that OS X doesn't actually support VROC. Don't create an array in the BIOS, do it in Disk Utility (software RAID). Or just use them as totally separate devices.

If your PCI-e SSDs don't show up, after turning RAID features on you want them to appear as... I forget the exact terminology, right now. Non-raid device, or non-attached device. That sort of thing.

 

[kylec]

However, I should also add that I've seen claims that only the expensive boards with the PEX chips actually allow all lanes to be used in OS X. I'm in the process of evaluating this for myself, now. I'll let you know how it works out with the MSI X299 Pro that I got recently.

 

[hotbullet]

However, I should also add that I've seen claims that only the expensive boards with the PEX chips actually allow all lanes to be used in OS X. I'm in the process of evaluating this for myself, now. I'll let you know how it works out with the MSI X299 Pro that I got recently.

My Friend has msi board cant remember the exact name it came with extra nvme to pcie that can use two card. both the card are shown automatically.

In my case how do i know which one is bifurcated slots (bifurcated is after turning on vroc? before turing on it is slot3?) ioreg will say what it is if hackintosh can not see the device? would you mind to look at my ioreg? i have attached.

thanks.

 

[kylec]

The card they include is a bifurcator. Or whatever the term is for the 4-way ones: PCI-e x16 to 4x PCI-e x4. So, enable bifurcation on any slot that has this type of thing (but note that some boards do it automatically). I like to reserve the x16 slots for GPUs, so I use the x8 to 2x x4 bifurcation adapter made by Supermicro.

Just look in the Hackintool PCI device list. It's the easiest way to see whether the problem is with a device driver or not. If it doesn't appear in the list, then keep trying different BIOS settings.

With my MSI, the bifurcation settings are in a menu labeled "VROC," but that's not really what they're about. It just has an "enable" for each slot. Again, there's more granular settings available if you go into the IFR variables.

Another label you may see is "IIO." This is the term for the channels (4 of them) from which the processor's PCI-e lanes are allocated.

 

[Kevin]

Hi @kylec were you able to find out how the PCIe lanes on the MSI X299 Pro are used in OS X? I'm debating starting a Cascade Lake-X Core i9-10920X system but am having trouble picking out a mobo. Do you have one you prefer? Thanks!

 

[kylec]

No, sorry. Unfortunately, I wrote all of this up, but then I had to stop working on that system with the MSI board.

 

[etorix]

The answer to that question would ideally be provided by a block diagram, and there's one at page 20 of the manual… but it's the most useless diagram I've ever seen. Just arrows, no indication of the actual number of lanes or even which PCIe slot is which.
If I were looking for a board, such a joke of a manual would strike MSI out of my list!

Otherwise, if you do consider investing in a dead socket, you may have a look at C422 boards for Xeon W-2000 CPUs. RDIMM is cheaper than UDIMM, especially if you find second-hand bargains from refurbished servers. All Xeons W-2000 have the maximal number of PCIe lanes (no headaches), and server/workstations board usually come with proper block diagrams.