Are there any PCIe Switch Risers?

[Zarathustra[H]]

PCIe Switches are a thing. They are expensive, use power, and introduce some latency, but they exist and work.

PLX was probably the most famous until they were absorbed by Broadcom, but there are other brands as well. I believe TI makes some, and there is also a company named Microchip that appears to be in the market.

We often se them integrated into enterprise hardware (either motherboards or SAS controllers, etc)

The question is, are there any general purpose risers one could use?

An example use case could be as follows:

Your motherboard has a 4x Gen5 or 4x Gen4 slot. You need to use an 8x Gen3 expansion card. The 4x Gen5 and Gen4 slots have more than enough bandwidth to support the 8x Gen3 card, but if you just install it, it is going to run in 4x Gen3 mode and choke.

The solution would be a PCIe switch riser that inserts into the slot, and communicates with the motherboard at 4x Gen5 or Gen4 speeds, and converts all of that bandwidth to 8x Gen3, allowing the 8x Gen3 expansion card to work at full bandwidth.

This could be either a straight up riser allowing for the use of a half height card on top of it, or it could use a cable and breakout board to allow you to install the 8x gen3 card somewhere else.

Heck, in the case of the latter, it could even be designed to go into a gen5 or gen4 m.2 slot.

The technology to do this exists, but the question is, has anyone actually done it?

I'd happily pay a few hundred dollars for something like this. I can't be the only one.

I've done some googling, but all I can find are some half-assed mining adapters that look like they would be crap. Has anyone seen anything better?


The closest I have found thus far is this one electrical engineer in Germany who seems to run his own business:

https://c-payne.com/collections/pcie-packet-switch-adapters-gen4

His products are pretty cool, but are quite overkill for what I have in mind.

 

[cdabc123]

No, just dedicate a number of pcie lanes and call it good, pcie bandwidth is ample for most devices. The problem is modern consumer setups have a minimal amount of pcie resources.

It not worth introducing the latency and challenge of emulating multiple slower pcie lanes on a pcie 5.0 lane. Most older devices that did switching used propitiatory standards and slots to the switch.

Just use your pcie lanes conservatively and remember most devices do not need the full bandwidth they are electrically capable of. Im pretty disappointed with the ability of consumer mobos to handle more then afew pcie devices. seems like a step back from x99 or older prosumer setups.

 

[Zarathustra[H]]

No, just dedicate a number of pcie lanes and call it good, pcie bandwidth is ample for most devices. The problem is modern consumer setups have a minimal amount of pcie resources.

It not worth introducing the latency and challenge of emulating multiple slower pcie lanes on a pcie 5.0 lane. Most older devices that did switching used propitiatory standards and slots to the switch.

Just use your pcie lanes conservatively and remember most devices do not need the full bandwidth they are electrically capable of. Im pretty disappointed with the ability of consumer mobos to handle more then afew pcie devices. seems like a step back from x99 or older prosumer setups.

Well, I'm willing to mess with finicky systems to make this work.

No system with less than a 16x-8x configuration is of any use to me at all. It just doesn't fit in my setup and where I want to go with things.

Neither the new Threadripper nor Intel's Xeons are real HEDT platforms, in that they perform so much worse than client CPU's

Pretty much all of the enterprise hardware I would put in the 8x slot has been known to be finicky if not operating with all lanes.

I see no other way forward, even if I have to commission some electrical engineer to make these damn things for me. Maybe I can turn it into a business

I don't see how anyone can use a PC without at least 40 available PCIe lanes, and I shouldn't have to sacrifice performance in order to get it.

 

[Zarathustra[H]]

It not worth introducing the latency and challenge of emulating multiple slower pcie lanes on a pcie 5.0 lane. Most older devices that did switching used propitiatory standards and slots to the switch.

By the way, Consumer PCIe switching is by no means dead.

Its built in to just about every consumer motherboard chipset.

How do you think the AMD X670E grabs only four Gen5 lanes from the CPU and uses those to provide things like USB, SATA as well as 12 PCIe gen4 lanes and 8 PCIe Gen 3 lanes?

While I wish at least one of the many motherboard makers would just give me those 8 gen3 lanes in an 8x slot, that just isn't happening for some reason. But if AMD themselves can do it and do it well in the chipset, why not in a 3rd party peripheral?

Heck, I have an LSI 9300-16i, which is essentially two 9300-8i's glued together on the same board using a PLX chip. Why not have it as a plug in adapter?

 

[toast0]

What you're asking for makes sense to me, I don't need it, but it makes sense, but I haven't seen anything like you're asking for. I think C-Payne used to post in hardforums, not sure if he still does.