Quad M.2 SSD Cards with a PLX chip - An option for getting your PCIe lanes back

Hardware Hub Motherboards
1

This is a follow-up to an old thread I posted 2 couple weeks ago.

My complaint is modern motherboards don’t have enough PCIe slots. For those of us that have networking cards, lots of M.2 cards, storage media, video cards, or lots of other PCIe hungry devices, what are we supposed to do? How are we supposed to give lanes to all the devices in our builds? Because like the rest of you, I don’t want to drop effectively a huge premium on a modern HEDT platform just to get more PCIe lanes. So what is a PCIe enthusiast to do?

I found a solution. It’s not the best one, but it’s worth exploring:

I recently purchased this:

https://www.aliexpress.us/item/3256805724779576.html

Found a cheaper one on Amazon:

This is PCIe gen 3 x16 to quad m.2 adapter. But if you look at the spec page, this is actually just a PLX8747 PCIe switch chip on an expansion card:

In other words, all this card does is create more PCIe lanes where there were none before. And PCIe lanes don’t just have to be used for SSDs, they can be used for anything. So I purchased this expansion card, and ran several tests on it. I bought this to be the guinea pig and answer several questions to the three other people out there who have the same specific problem:

All tests were done on a Gigabyte X99-UD4P Motherboard with a Xeon E5-2697 v4.

  1. Does this device require PCIe bifurcation to work?

No. One of the reasons I specifically bought this card is because no bifurcation is required as my motherboard doesn’t support bifurcation. Just plug it in and go. The PLX chip handles everything.

  1. Can you use things other than M.2 SSDs in this?

Absolutely. I have one of these M.2 to USB C front panel header adapters hooked up to the expansion card right now and it works great:

https://www.aliexpress.us/item/3256806770633853.html

  1. Can you boot from the SSD?

Yes, you can boot from this card. I have my Intel P4800X SSD connected to this card right now.

  1. Does drive information display correctly in the bios?

Yes. All drive information including the SSD displays in the BIOS and in Windows. TRIM and garbage collection both work on my other SSDs.

  1. Can you shove this card into a PCIe slot on a motherboard with fewer lanes than the card has?

Yes, this works.

I was skeptical this was going to work at first because this is a PCIe switch. Some Quad m.2 cards require all the lanes present on the card to be connected to the motherboard. But not this one!

I taped off most of the PCIe lanes on the card except for enough contacts to effectively turn it into a “PCIe x1” expansion card. After trying this, my PC was still able to boot just fine and all other SSDs were visible. Obviously bandwidth took a massive hit, but it worked.

So where would this be useful?

You could buy a cheaper B-series AM5 motherboard with two expansion slots. Then shove this quad m.2 ssd card in one of the bottom expansion slots (that is usually PCIe x4). This will effectively give you access to four more m.2 slots which can be used for anything from wifi to extra SATA ports to even 10GB ethernet.

What are the downsides?

The biggest downside I see is speed. This is a PCIe gen 3.0 device. Now this isn’t the biggest deal in the world for now, but it will be in the future as I/O becomes ever faster.

I think I may have just solved my extremely first-world problem. Hopefully this is useful to someone else.

5 Likes
2

Useful to know, yes. IMO PCIe speeds above gen 3 are only useful if you need to move a lot of data very fast. Most people don’t :dash:

[edit] The Amazon card is not available in my country, bummer :rage:

3

If memory serves, PCIe Gen3 x4 is 4ish GB per second.
Closest network spec would be SFP28 at 25Gbit/s, which would not saturate that Gen3 x4 link.

4

There are some u.2 options as well like the Viking U20040-02. As long as you can keep it cool. :slight_smile:

5

You’re going to need to be very selective with your SSDs. Depending on where you stick the assemblage, there might be no clearance for heat spreaders and such.

6

checks ebay

What… exactly is this thing? Is it just a U.2 to quad m.2 ssd adapter? I’m assuming underneath the heatspreader is a PLX chip?

7

It seems your evaluation is correct. Needs a high airflow environment (i.e. servers!) to keep cool.

Meanwhile, I found a cheap quad M.2 card, claiming to have the PLX8747 PCIe switch chip on Aliexpress. I ordered one, which will be shipped after Lunar New Year, and then I’ll give it a test on an old AMD system with an actual PCIe x1 slot and a mining-era contraption to expand that x1 slot into x16. I’m not gonna post the link yet, as it might be bogus. Although the brand itself is a better reputed one I believe. We’ll see :person_facepalming:

8

Yup, 8 GT/s 128b/130b, so 985 MB/s bus capability per lane and 3.94 GB/s for an x4 link. Max data transfer rate after protocol overhead’s ~3.5 GB/s, so full rate 25 GbE’s about 90% utilization.

Also I don’t know of any drives with cache folding rates above 2.4 GB/s. So it’ll probably be a while still before 3.0 x4’s likely to constrain writes past pSLC.

1 Like
9

Nice post. I’ve also been ‘plagued’ by this først world problem. I already have 4 m.2 SSD’s and I hate having such fast storage I can’t use for anything.

For me it’s not about the outright speed, but m.2 are cheaper than 2.5" SSD (in my country). So I don’t mind m.2 drives share PCIe bandwidth. It is still faster than SATA. One problem might me compatibility across CPU platforms. But still it would be nice seeing this work for people.

10

If you want 4 good things (10Gbe, 2 USB-C 10 Gbps and 2 M.2 slots) on a single card that also doesn’t require bifurcation I can recommend this card:

I use it myself and it’s a fine thing imho.
You can safe some space with it and still get 2 m.2 pcie slots that can be used.
I don’t have much in the way of other m.2 cards than storage so I haven’t tested other cards.

1 Like
11

Yeah, U.2 to quad m.2. However each port can do Pcie x2. Which makes it a little more interesting.

12

That might be useful if you are REALLY constrained for space. But i’m not. And a $120 quad m.2 adapter works just fine for a fraction of the price.