[SOLVED] Can anyone explain why an nvme pcie card only works with two ssd's but a third nvme can be added in its own pcie slot.

[Alan Alan]

This is certainly a mystery to me. The nvme support card that holds 4 ssd's is an X16 , The other separate card that only holds 1 nvme ssd is an X4 card. It seems each pci-e X16 slot would have its own data pins connected to the micro. So it seems the x16 card should show all 4 ssd's. Yet it only allows 2 ssd,s I figured that's all I could yet. Yet I get 3 nvme ssd's total if I add another card into another the third pcie slot. I know they want the video card in pcie slot #1 for best results, but why does that matter. I have three X16 slots, are they not the same? Would the video card have limited data transfer if used in slot three or something? If so, why even had three X16 connectors. As it stands, the X16 nvme works with up to 2 ssd's in pcie slot number two. And the single nvme X4 works in pcie slot # three. So I have a total of 3 individual nvme ssd's working but why couldn't I get more than 2ssd's to work in the card that holds up to 4 ssd's? Something tells me you can't really make full use of three X16 cards. I really don't get it. They say an X4 card uses 1 lane, an X8 uses 2 lanes and the X16 uses 4 lanes. So why can't the single cards that holds up to 4 ssd's use all 4 lanes, one for each ssd. This really makes no sense. Maybe the lanes may be set to 4 on pcie slot number 1 "if it's in there" and trimmed down to 2 lanes on pcie slot 2 and 1 lane on pcie slot 3. I know some mobo's have more lanes such as the x299, I have the 370a with fewer lanes so the X299 board might be intended as a server or something that can actually use three separate pcie X16 with 4 lanes on each slot. I'm beginning to think if I had put the card that holds 4 nvme ssd's in pcie slot 1 where the video card is, it may have actually acknowledged all 4 ssd's. But then the video card if put In pcie slot #2 may only be able to use 2 lanes limiting its data flow. How does this all really work? Anyone know???

 

[hotaru.hino]

First of all, what PCIe cards and motherboard are you using? Then we can probably help. Otherwise we're pretty much going in blind here.

Secondly, how many lanes a PCIe card may appear to have may not be what it actually needs or has connected. Manufacturers may due this for cost reasons as it's actually more effort to etch away connectors on a PCB. That or they don't want to stock a bunch of different sizes.

Thirdly, yes some PCIe 16 lane slots may not be wired up for 16 lanes, or even say 8 lanes. It's done this way again to simplify manufacturing (the board makers only need to stock x1 and x16 slots).

 

[CountMike]

In addition, not all PCIe (including M.2) are likely all connected to CPU PCIe lanes and others are likely to be connected to chipset.

 

[Alan Alan]

First of all, what PCIe cards and motherboard are you using? Then we can probably help. Otherwise we're pretty much going in blind here.

Secondly, how many lanes a PCIe card may appear to have may not be what it actually needs or has connected. Manufacturers may due this for cost reasons as it's actually more effort to etch away connectors on a PCB. That or they don't want to stock a bunch of different sizes.

Thirdly, yes some PCIe 16 lane slots may not be wired up for 16 lanes, or even say 8 lanes. It's done this way again to simplify manufacturing (the board makers only need to stock x1 and x16 slots).

https://www.newegg.com/kingston-kc1000-480gb/p/N82E16820242445?Item=9SIAADF6YT5396

Are you a human?

www.newegg.com

https://www.amazon.com/ASUS-M-2-X16...ocphy=9022889&hvtargid=pla-659234806310&psc=1

Top link = single pcie nvmed
2nd link = mobo
3rd link = quad ssd holder

Not sure what they did, get what you mean about etching but fail to see why I had to use two cards, The kingston is actually a short pcie connector so no etching needed. Doubt any etching on the asus as it actually is a X16. I'm inclined to think there is some sort of dynamic assigning done to the lanes. Perhaps Pcie slot 1 gets lane priority, if it uses all 4 lanes the only 2 are available on slot 2 and possibly 1 or 2 or slot 3. Hard to say

 

[SkyNetRising]

How does this all really work? Anyone know???

Quite simple actually.

On ASUS Prime Z370-A only 1st PCIE x16 slot can operate in x16 mode (x16/x0)
Using 2nd PCIE x16 slot, switches 1st and 2nd PCIE x16 slots into x8 mode (x8/x8).
3rd PCIE x16 slot operates in x4 mode.

Your PCIE M.2 adapter with 4 NVME drives requires full x16 connectivity (4 times x4 per drive)
With 4 drives you can use it in 1st PCIE x16 slot only.

And graphics card has to be put in 3rd PCIE x16 slot (or 1st PCIE x16 slot switches into x8 mode).

 

[Alan Alan]

Quite simple actually.

On ASUS Prime Z370-A only 1st PCIE x16 slot can operate in x16 mode (x16/x0)
Using 2nd PCIE x16 slot, switches 1st and 2nd PCIE x16 slots into x8 mode (x8/x8).
3rd PCIE x16 slot operates in x4 mode.

Your PCIE M.2 adapter with 4 NVME drives requires full x16 connectivity (4 times x4 per drive)
With 4 drives you can use it in 1st PCIE x16 slot only.

And graphics card has to be put in 3rd PCIE x16 slot (or 1st PCIE x16 slot switches into x8 mode).

Nice, so they can switch dynamically... I do sincerely thank you for your expertise. Do they explain this in the mother boards manual? T did a search in the manual for X16 but nothing came up. Also there is no bios setting for any of the slots X value. It does appear that slot 1 is the only X16 slot unless video cards work on X8 slots. I tried the adapter in slot 3 with the graphics in slot 1; It only acknowledged two drives so it must be working as X8. I tried to find out if the RTX3070 card is X8 but even Nvidia doesn't say on their spec sheet. Lamers... Any suggestions on where to get a straight answer, there's nothing in the owners manual either. I would swap things around and should get the X16 to work on the adapter but might end up with X8 on the graphics. Not sure, would that degrade the graphics somehow?

 

[SkyNetRising]

I tried to find out if the RTX3070 card is X8 but even Nvidia doesn't say on their spec sheet.
I would swap things around and should get the X16 to work on the adapter but might end up with X8 on the graphics.
Not sure, would that degrade the graphics somehow?

RTX 3070 is full PCIE 4.0 x16 card. It can work in PCIE 3.0 x4 mode too. With somewhat reduced performance though.
(~10-20% performance loss depending on application and settings used).

NVIDIA GeForce RTX 3080 PCI-Express Scaling

NVIDIA Ampere finally brings PCI-Express 4.0 support to the high-end graphics market. The new interface promises twice the bandwidth of PCI-Express 3.0. We've setup an AMD Ryzen 3900XT system to test how various PCIe generations and lane widths affect gaming performance.

www.techpowerup.com

 

[Alan Alan]

RTX 3070 is full PCIE 4.0 x16 card. It can work in PCIE 3.0 x4 mode too. With somewhat reduced performance though.
(~10-20% performance loss depending on application and settings used).

NVIDIA GeForce RTX 3080 PCI-Express Scaling

NVIDIA Ampere finally brings PCI-Express 4.0 support to the high-end graphics market. The new interface promises twice the bandwidth of PCI-Express 3.0. We've setup an AMD Ryzen 3900XT system to test how various PCIe generations and lane widths affect gaming performance.

www.techpowerup.com

Gee, thanks, I guess it all worked out for the best then. I did a raid 0 on the 2 tb drives in the asusX16 and kept the os on the kingston. The speed of the raid 0 is very fast and minimizes video studder speeds. At best it's a relief to know that I didn't know what was happening and thanks to you it seems optimized. My original plan was to use intels Vroc for the raid and after getting all the parts it turns out it didn't even work. Asus found this out a year after it was made. So they said they weren't going to mention Vroc on future motherboards. I can't find the link right now. But even if it did work the graphic cards would have ended up in X4 mode and I would have never known it. So in reality you've been a great help. I'd still like to know where the lane info is in the user manual or how you know all of this, for future reference.

 

[Ralston18]

@Alan Alan

I removed your Best Answer award because Forum rules prohibit Self-awarding Best Answers.

From the context it appears that you intended to award @SkyNetRising a Best Answer.

You may do so, but as I understand Post #8, you need to click the Trophy icon in @SkyNetRising 's response - Post #7.

Thank you.

 

[Alan Alan]

@Alan Alan

I removed your Best Answer award because Forum rules prohibit Self-awarding Best Answers.

From the context it appears that you intended to award @SkyNetRising a Best Answer.

You may do so, but as I understand Post #8, you need to click the Trophy icon in @SkyNetRising 's response - Post #7.

Thank you.

DONE, I messed that up. However I still get better looking in the mirror everyday, lol.