PCI-E x16: Run graphics card and M.2 SSD at top speeds? And M.2 slot cannot give top speed.

[Deleted member 44897]

I'm running a fairly minimal system housing an Intel i6700K CPU, an NVidia graphics card and a Samsung 960 EVO M.2 SSD. The motherboard is a MicroATX Asus Maximus GENE VIII board with 16GB DDR4 memory.

I would like to run both the graphics card and the M.2 SSD at the advertised speeds. However, I'm unable to do so.

When running the SSD in the M.2 slot (as designed), it didn't reach top speeds as advertised. But when I inserted the SSD to the PCIE x16 via Asus Hyper X4 M.2 Add-On card, it does reach close to top speeds, which is satisfactory.

I'm confused. How is everyone praising this M.2 SSD at such high speeds when the M.2 slot can't achieve that? What's the catch? Why don't they mention, "Oh, but you need the PCIE X4 M.2 Add-On card to reach those speeds, by the way"?

Furthermore, in reference to the following image:

I have two PCIE x16 slots to work with. My graphics card is in the first one and my M.2 SSD (as stated) is in the second. I've heard that doing this cuts the bandwidth in half (x8 and x8)...but I'm told I wouldn't notice that difference in the graphics card. (I don't do any graphics/CPU intensive activity). And, with the M.2 sitting in the second PCIE x16 (via Add-on card), it's getting it's top speeds.

But I don't understand why I can have all of one, but only half the other...

AFTER-POST EDIT:
An Asus chat representative provided me with this information, credit the Intel specs sheet on the I6700K:

Is this my answer? That I can only use one x16 device at top speed?

Burning questions:
1) With this configuration, is it at all possible to achieve top speeds on my graphics card and the M.2 SSD? (I find it hard to believe that I can't.)
2) Could top speeds on both devices be achieved on a motherboard with three PCI-Ex x16 slots?
3) What about the Ultra M.2 slot I've heard about (utilized by ASRock)? How is that different from my M.2 and would that allow for the "top advertised speeds"?

Any insight and information would be much appreciated. Thanks in advance!

 

[TJ Hooker]

How did you come to the conclusion that the SSD wasn't getting it's max speed when plugged into the M.2 slot?

 

[4745454b]

How close do you get? What else might be using the M.2 slots bandwidth?

 

[Deleted member 44897]

How did you come to the conclusion that the SSD wasn't getting it's max speed when plugged into the M.2 slot?

Crystal DiskMark had reported it at about two thirds its advertised speed. But, while in PCI-Ex x16 via add-on card, it was closer to max.

Also, I don't know what else could be using the M.2 bandwidth. I have stated that all I have is the graphics card and the SSD.

 

[TJ Hooker]

Could you list the speeds you got with the M.2 slot, and with the PCIe x16 slot?

The M.2 slot goes through the Platform Controller Hub, and then over the DMI 3.0 interface to the CPU. Pretty much all peripherals/drives (that aren't connected to the direct-CPU PCIe lanes) go over this interface as well, and DMI 3.0 is limited to 4GB/s (i.e. PCIe 3.0 x4 speeds). So if you have any activity to other drives or peripherals, it could in theory cut into your M.2 slot's bandwidth. In other words, you can probably just put in the the M.2 slot and you'll never experience a measurable difference in performance compared to the PCIe slot during normal use.

But you're probably not going to be trying maxing out your SSD and another device simultaneously anyway, so this probably won't be an issue. Also, the only time you're going to actually get maximum advertised speeds (or close to) out of your SSD is running synthetic benchmarks, as no normal consumer use is ever going to max out the PCIe 3.0 x4 interface.

 

[Deleted member 44897]

I apologize for the delay. I ran Crystal DiskMark on the M.2 SSD in the PCI Ex x16 slot, the x4 slot, and the M.2 slot. Here are my results:

PCI-Ex x16 slot:

PCI-Ex x4 slot:

M.2 slot:

(These tests were run at night, within fifteen minutes of each other.)

I am actually surprised at the M.2 slot readings. Six months ago, when I built the system, the M.2 readings were about half that (similar to those of the x4 port). There have been no hardware changes since.

I guess I've answered my own dilemma. I am currently getting top speeds with my M.2 SSD in the M.2 slot now.

 

[4745454b]

In that case I'm glad it worked itself out! LOL.

 

[blazeaglory]

Could of just been throttling itself because it might have got too hot?

 

[Pavel_]

LOL. Good question! Here i am trying to explain. Maybe somebody will see it and that would be useful.
1.When u choosing m2 ssd, first thing u need to decide is raeding speed ( if reading speed is 1500mb/s or below u can use motherboards with m2 pcie x2 slot and it would be enough) motherboards with this slot can be smaller and price can be much lower.
2. If u need really outstanding fast ssd with reading speed like 3200-3500 mb/s u should pa attention and choose apropriate motherboard
(u need m2 X4 pcie slot NOT X2 to achieve reading speed like 3200 mb/s. Motherboards with m2 x4 slot always more expensive and rare. They are often have 2 m2 x4 slots and 4-8 ddr ram slots and they big, not mixro atx or mini atx.
3. If u don't pay any attention at all or u miss this things and bought m2 ssd or don't have any m2 slot either u can use m2 x4 to pcie x16 adapter and use it in your pcie x16 second slot (if you have more than one your motherboard).
4.m2 ultra is designed for ssds like intel Optane or new kind of ssd, which is not faster than samsung 950/960/961 pro/evo. they often small and they designed to cache ur files if u have ssd+hdd combination.
5. So basically it's ur fall that u dont pay attention. u need to: a.change motherboard or b. use your m2 ssd in pciex16 via adapter and loose ur 200-500 mb/s reading speed. Coz, once again the problem is:
m2 x4 speed - 3200 mb/s - 3500 mb/s
pcie x 16 speed - 3000 mb/s
m2 x 2 speed -1500 mb/s
msata speed -500 mb/s - 700 mb/s
sata speed 300 mb/s - 500 mb/s

ur ssd( samsung 950/960/961 pro/evo) speed 3500 mb/s

 

[TJ Hooker]

Motherboards with m2 x4 slot always more expensive and rare. They are often have 2 m2 x4 slots and 4-8 ddr ram slots and they big, not mixro atx or mini atx.

No, (modern) mobos with PCIe 3.0 x4 M.2 slots are not rare, are not necessarily expensive, and they're not limited to full size ATX. Here's a micro ATX mobo with PCIe 3.0 x4 M.2 slot for under $60.
https://www.newegg.com/Product/Product.aspx?Item=N82E16813130991&ignorebbr=1&nm_mc=AFC-C8Junction&cm_mmc=AFC-C8Junction-PCPartPicker,%20LLC-_-na-_-na-_-na&cm_sp=&AID=10446076&PID=3938566&SID=

m2 ultra is designed for ssds like intel Optane or new kind of ssd,

Ultra M.2 is the same as PCIe. 3.0 x4 M.2. Which is basically the standard PCIe M.2 now.