mainboard pcie slot layout and lanes (upgrade advice)

[tobbe]

it has been a while since i built my last computer but recently i ran into problems mainly with lack of rebar support on one of my linux boxes, so i started to look around for what more recent mainboards have for pcie slots and lanes.

looks like now most mainboards have one x16 slot with 16 lanes and rest is perhaps physically a x16 slot but only 1 lane is wired up.
this created problems because i have both a sas controller (lsi 3108) and a dual 10gbit nic plus (reason for the rebar issue) a gpu.

even my old z170 skylake mainboard have better choices for pcie lanes (unfortunately also no rebar support or i would have used it)

so what i’m looking for is decent options for a not too expensive upgrade that would allow me to reuse the existing ddr4 memories i have.
likely some older intel gen 12,13 or 14 cpu + mainboard, i have little or no use for m.2 slots at most one to boot from.
i assume my only option to fit all 3 cards is to “steal” the pcie lanes from one of the m2 slots via a riser or perhaps use pcie bifurcation on the first x16 slot since i only need 8 lanes for the gpu.
but then what about mounting it in the computer?
would a matx mainboard be better to leave more empty space for riser cards?

side note:
the current one is a supermicro C7X99-OCE mainboard and i was hoping to be able to turn on above 4g decoding plus pci=realloc in proxmox to get larger bar but that did not work.
the bios on this mainboard sucks a lot, it is super easy to run into a bios reboot loop if you try to turn off legacy boot and csm.
i lost track of the number of cmos resets i did trying to get it working, eventually giving up.

best upgrade is not having to do the upgrade in the first place and thats what my initial plan.

[lemma]

Variations of this thread happens on a regular basis around here. TL;DR: x8+x8 switched PEG off the current x28 sockets is expensive, the selection of three slot boards with x8+x8+x4 is limited, x16+x4+x4 can also be a bit hard to find, and x8+x8+x8 isn’t a thing.

For AMD, X870E Carbon or B850 LiveMixer as a lower cost non-switched approximation. But those are DDR5. In AM4 I don’t know any easily available three slot boards with x8+x8 PEG.

For Intel, MW34-SP0. With DDR5, Z690 Carbon, Z690-Z790-Z870 ProArt, W680 Ace, Z690+Z890 Aorus Xtreme. Taichi is two slot but Z890 LiveMixer’s again a non-switched approximation.

Probably there’s a few others but the above should be a decent starting set. Also W880 but I think it’s not shipping yet and definitely won’t match the cost objective once it is. But…

@tobbe

not too expensive upgrade

…don’t see that happening unless you find something used that’s underpriced or happen to also already have some DDR5.

@tobbe

pcie bifurcation on the first x16 slot

It can work with a breakout card and risers to the GPU and HBA. But I’m not sure 5x8 implementations exist yet and 4x8 with the needed redrivers/retimers and riser quality easily prices into the upper tier motherboard range with a lot more hassle. If 3x8’s ok that’s doable without signal regeneration on the breakout card, lower cost risers, and less care in parts selection. Though by the time you buy the parts, solve the mechanicals, and validate the signal integrity a three slot board starts to look not so bad.

@tobbe

would a matx mainboard be better to leave more empty space for riser cards?

Doubt it. Also if you can find W680D4U it probably won’t fit the budget and the mechanicals are tricky.

@tobbe

best upgrade is not having to do the upgrade in the first place

If you don’t want to fight board layouts, plan to phase out SAS for NGFF and ASMedia SATA with 3x1 or 3x2 uplinks, maybe RTL9101. Or start budgeting for MCIO and planning U.2/3/E1.S/E3.S thermals. Not that NGFF thermals are simple.

Mobos with dual 10 GbE are mostly workstation and server sockets and the few desktop socket server boards tend to be unobtainium. X870 Taichi Creator’s 10+5 GbE, which is both about as cost effective and close to 10+10 as it gets otherwise.

[homeserver78]

@lemma

In AM4 I don’t know any three slot boards with x8+x8 PEG.

Asus ProArt B550-CREATOR is x8+x8+x4 (all in physical x16 slots). (Plus 2x x1 slots.)

Or I might say it was x8+x8+x4 since it’s no longer sold.

[twin_savage]

The hard part about this is it’s typically the lower end chipsets that support DDR4 on LGA1700 and thus bad PCIe breakout, but good boards do exist.

There are boards like the ADS630 that support PCIe x16+x4+x4+x4+x4+M.2s+on board 10GBe but I think this might be overkill with PCIe slots and features (also kind of expensive @ 700USD).

Asrock had the IMB-X1712 and IMB-1712 that would have worked but the stock of these has dried up. Stock of IMB-X1314 still exists, and it does fulfil your requirements, but is mATX so only has a x8+x8+x4+x4+M.2s configuration as opposed to even more PCIe.

@tobbe

“steal” the pcie lanes from one of the m2 slots via a riser or perhaps use pcie bifurcation on the first x16 slot since i only need 8 lanes for the gpu.
but then what about mounting it in the computer?
would a matx mainboard be better to leave more empty space for riser cards?

I see PCIe risers and adapters advocated for far too often on forums in general, they are a headache and prone to random failure and IMO should only be used as a last resort with the expectation they will perform like a heavy overclock, probably maybe stable but not guaranteed to work over the long term.

[lemma]

@homeserver78

Or I might say it was x8+x8+x4 since it’s no longer sold.

X570 ProArt too. B650 ProArt is a popular AM5 suggestion in this niche as well, but it’s down to a tiny amount of old stock around here that’s “only” marked up like 1.6x (as opposed to 2-4x). Ironically, X670E ProArt drops to x8+x8+x2.

IMO Asus’s combination of security vulnerabilities, bloatware, predatory support, high brand tax, and BIOS crippling’s unappealing. But it seems to work for some folks. ¯\_(ツ)_/¯

[xzpfzxds]

By upgrading, what do you want to solve other than getting a BIOS with working PCI options?

The PCI connectivity layout of gaming boards is extremely limiting, so I think the only options using DDR4 (what type? UDIMM/RDIMM?) will be Zen3 Threadripper if you want a bump in CPU performance.