Woud x8/x8 bifurcation work for a 4-port U.2 adapter with 2 drives?

I bought a 10GTek U.2 adapter with 4 connections and I was not aware bifurcation was not a thing on the Asus B660M board I bought for building a NAS.

After more research it seems 4/4/4/4 split is basically Bigfoot in the normy-world, and 8/8 is the best deal intel is able to give me. Since I need micro-ATX, to fit in the Jonsbo N4 case, Z790 seems to be the only option as far as I can tell.

Before I make another botched purchase, I need to know if I split up the x16 to 8/8, would the U.2 adapter work if I plugged the two drives I have in the appropriate sections of the card? Like the traces go to different pins from the connectors, I would use the 1st and 3rd connectors. Would that make it work?

Edit:
The parts if relevant:

  • Jonsbo N4 case
  • Intel 12100T 35W with Noctua NH-L9x64
  • ASUS TUF B660M-E D4
  • 4x8GB G.Skill Trident-Z 3600 something I had in the drawer
  • 2x KIOXIA XG6 1TB nvme
  • 4x 12TB Seagate IronWolf (ST12000VN0008)
  • Intel Optane 905P 480GB
  • Kingston DC1500M 7.68TB

AMD seems to have better bifurication support in general. But a quick search seems to suggest it’s still limited to ATX boards.

If you only have x8x8 from x16, and if you have 4xU.2 adapter, then yes it would work if you plug in slot 1 and 3. You’d waste the other 8 lanes but yes it is possible.

Something like this Delock Products 90169 Delock PCI Express 4.0 x16 Card to 4 x internal U.2 NVMe SFF-8639 - Bifurcation (LxW: 288 x 122 mm) or this Delock Products 90077 Delock PCI Express 4.0 x16 Card to 4 x SFF-8639 NVMe - Bifurcation - Low Profile Form Factor

1 Like

In short - no.
For assus bifurcation support check here
In general intel desktop platform don’t support lower bifurcation than x8/x8.
AM4/5 platforms support the bifurcation pattern you need. x4/x4/x4/x4

“Before I make another botched purchase, I need to know if I split up the x16 to 8/8, would the U.2 adapter work if I plugged the two drives I have in the appropriate sections of the card?” - In theory it should, but most likely not. Your board is relatively low end and not on the supported list Usually x8/x8 is applicable for split between two physical slots.

I got the ASUS Prime Z790M-Plus board. It works as I hoped in my initial post.

In the bios I split up the primary x16 slot to x8/x8 and the U.2 adapter was able to function. Plugged in the NVMe and Optane drives to the top and 3rd from top connectors and both are visible and usable.

Yes I’m aware, I won’t be able to use 4 U.2 drives, but I don’t need to.

Also this board is so cheap… 1gig network, no M.2 latches to secure drives (the B660M TUF had them), the IO shield is the ancient silver one from 30 years ago. Yeah it’s a Prime board, but damn. They did Z790 dirty.



Some observations to post above:

  • if adapter is priced reasonably, then it requires bifurcation. Necessary pcie switches that obviate bifurcation requirement are very expensive, many multiples of total card cost like this even.
    • seller mentioned bifurcation requirement is broken chineglish way, so they didn’t lie to you
    • 10GBE tek makes pcie switch adapters, entire lineup is here, cheapest PCIE3 capable start at 150 USD+
  • Bifurcation is available on some consumer boards, but it is limited and not guaranteed to be there. You must verify support board by board.
    • if its available, then its available only on pcie ports directly connected to cpu
    • On consumer platforms, that is only the first 1x16 PCIE slot ( or first and second if they share bandwidth)
      • If slot is PCIE5 , then generally only X8/X8 bifurcation is available ( nobody seems to know why only that)
      • If slot is PCIE4, then X4X4X4X4 is usually available

Not a hard and fast rule - there are a few consumer AM5 boards that support PCIE5 x4x4x4x4 (or even x4x4+x4x4)