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Confused about M.2 PCIe and "Regular" PCIe


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#1
Spyderturbo007

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I'm looking to build a new gaming rig and am confused about the relationship between the M.2 PCIe and the "normal" PCIe that I would use for a video card.

For example, I'm looking at this motherboard, M.2 NVMe and video card:

Samsung 950 Pro M.2 PCI-Express 3.0 x4

http://www.newegg.co...Item=N82E168...

MSI Gaming X99A Gaming 7

http://www.newegg.co...Item=N82E168...

GeForce GTX 960 4GB

http://www.newegg.co...Item=N82E168...

My confusion stems from the overlap between the two types of PCIe slots.

If I install the M.2 PCIe SSD, does that essentially "use up" any of the PCIe slots? Similar to how using a regular M.2 SATA drives disables some of the regular SATA ports? Or is there no overlap between the two?

I'd like the ability to upgrade to SLI down the road and don't want to bottleneck myself out of the gate.

Also, will that motherboard allow maximum performance out of the SSD? The SSD is labeled as NVMe, but I can't seem to find that exact wording on the motherboard page. Just the overlap of the M.2 PCIe designation.

Thanks!

 


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#2
terry1966

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yes it uses up pci-e lanes, a cpu motherboard combo has a set number of pci-e lanes, the number of lanes depends on the cpu and chipset.

so those pci-e lanes will need to be shared amongst all devices that need to use a pci-e lane.

eg. when running a single graphics card it will run using 16 pci-e lanes but when you use dual cards each card will use 8 lanes each for a total of 16 lanes (for a cpu that has 16 pci-e lanes.).

 

the m2 pci-e ssd though will not use any of the cpu lanes available to the graphics cards and will use the chipsets pci-e lanes which use a separate connection, dmi-2.0x4 for the x99 motherboards i believe, to communicate with the cpu.

 

:popcorn:

 

forgot to say yes the motherboard will allow the maximum speeds of the nvme drive because it uses m2 gen3x4 pci-e connection, only thing i can't say for definite is if you can use it as a boot drive because the bios/uefi has to be compatible too but i would think it probably can be booted from.

 

as an aside, i put a similar nvme drive (sm951) in my last build and the speeds were awesome, over 2000MB read, i've never seen anything come close, even in ssd raid 0 setups, to those speeds.


Edited by terry1966, 22 March 2016 - 07:22 AM.

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#3
Spyderturbo007

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Awesome.  Thank you so much.  I was concerned that it would essentially rob PCIx lanes from the GPU.

 

I'm wondering how I determine if the NVMe slot is bootable.


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#4
terry1966

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no idea to be honest, mine showed up in the uefi and i could install an os to it (was on a z170 skylake system.), i'd assume if it's not bootable then it won't be seen in the uefi and will only show up as a usable drive after an os is up and running.

 

if it doesn't show up in the uefi and you don't get an option to install the os to it, try updating the uefi to the latest version and then you might be able to use it as a boot drive.

 

:popcorn:


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#5
bassfisher6522

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The key point to remember is your mobo and how it's specifically laid out to use M.2 PCIe lane. With my mobo (Gigabyte GA Z97 Gaming 7), If I use the M.2 port it knocks out 2 SATA ports because it uses the same PCIe lane as those 2 SATA ports. Just something to keep in mind when looking for mobo's and to confer with the mobo manual online for specific details. 


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#6
Spyderturbo007

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I got everything built, but unfortunately, I'm stuck at 10Gbps.

 

Mobo - MSI Gaming 7 X99a
OS - Windows 7 x64
GPU - Sapphire Nitro Radeon R9 390x 8GB
Intel i7 5820k

I installed the NVMe drivers from Samsung's website and have the drive installed in the motherboards M.2 slot between PCIe slots 3 & 4. The GPU is in slot 1.

From MSI's website it says:


• 1 x M.2 port, supports M.2 SATA 6Gb/s module* or M.2 PCIe module up to 32Gb/s speed**
- M.2 port supports 4.2cm/ 6cm/ 8cm length module
- M.2 PCIe module does not support RAID 0, RAID1, RAID 5 and RAID 10.

* The SATA Express port or SATA5~6 ports will be unavailable when installing the M.2 (Gen2 x2 mode) module in the M.2 port.
** Intel RST does not support PCIe M.2 SSD with Legacy ROM.

There are some PCI options in the BIOS that I've tried changing, but I'm not sure what they do.

PCI Latency Timer (I didn't change this one).
M.2 Source Link (Set to Auto)
M.2 PCH Strap (Set to M.2 PCH PCIE)

If I set the Source Link to PCH, it drops down to 5Gbps.

The Magician App says "Link Speed Current: 10Gbps, Max10Gbps. Link Width Current: x4, Max :x4.

Any thoughts on how I can fix this?


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#7
terry1966

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sorry can't offer any solutions at the moment except to read your motherboard manual again, does look to me though like you have the correct setting.

eg. "M.2 PCH Strap (Set to M.2 PCH PCIE)"

 

can you download and run crystal diskmark just to double check what speeds your getting. :- http://crystalmark.i...rk/index-e.html

 

:popcorn:


Edited by terry1966, 02 April 2016 - 02:07 AM.

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#8
iammykyl

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Gday.

Have you managed to get the correct speed from the 950 Pro?   Do you still need some help?


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