PCIe lane bottleneck?

[Petrie X]

I was planning on getting a m.2 ssd for boot and core apps. I currently have a i7 6700k and a gtx 1080 paired with a gigabyte gaming z170mx mobo. Would a m.2 ssd make my GPU run only on 1x8 PCIe lanes? 

[SageOfSpice]

Why would it? They are separate lanes?

[Sakkura]

The PCIe lanes for the M.2 slot come from the chipset, so it doesn't affect the graphics card at all.

 

The CPU has 16 PCIe lanes, mainly for graphics cards, while the chipset has an additional 20 PCIe lanes for other things including M.2 slots.

[Electronics Wizardy]

No as the ssd uses pcie lanes from the pch not the cpu.

[Petrie X]

4 minutes ago, Sakkura said:

The PCIe lanes for the M.2 slot come from the chipset, so it doesn't affect the graphics card at all.

 

The CPU has 16 PCIe lanes, mainly for graphics cards, while the chipset has an additional 20 PCIe lanes for other things including M.2 slots.

Thanks i was just confused

[Zyndo]

Since we're here, I've often wondered. I'm aware the M.2 port comes off of the motherboard's chipset, but if I were to put in an PCIe adapter, and ran an M.2 card off of a PCIe port instead of the dedicated M.2 slot, does it then come out of my CPU's lanes? or is the hardware intelligent enough to still notice it as an M.2 drive and route it through the chipset lanes instead?

[Electronics Wizardy]

16 minutes ago, Zyndo said:

Since we're here, I've often wondered. I'm aware the M.2 port comes off of the motherboard's chipset, but if I were to put in an PCIe adapter, and ran an M.2 card off of a PCIe port instead of the dedicated M.2 slot, does it then come out of my CPU's lanes? or is the hardware intelligent enough to still notice it as an M.2 drive and route it through the chipset lanes instead?

Depends on the mobo.

[Zyndo]

32 minutes ago, Electronics Wizardy said:

Depends on the mobo.

Would there be a way to predetermine this before purchasing a motherboard? Something on the spec sheet or in the manual that could give a definite answer? I'm considering going X99 on my next rig (or whatever the equivalent of X99 is at that point) and I want to do something like RAID 0 2 NVME m.2 drives (like a pair of Samsung 950's). But most motherboards that I tend to like, don't tend to come with 2 m.2 ports. If i end up doing SLI in that system, I don't want to be shooting myself in the foot with GPU lanes because I want to SLI m.2 stuff.

[Electronics Wizardy]

42 minutes ago, Zyndo said:

Would there be a way to predetermine this before purchasing a motherboard? Something on the spec sheet or in the manual that could give a definite answer? I'm considering going X99 on my next rig (or whatever the equivalent of X99 is at that point) and I want to do something like RAID 0 2 NVME m.2 drives (like a pair of Samsung 950's). But most motherboards that I tend to like, don't tend to come with 2 m.2 ports. If i end up doing SLI in that system, I don't want to be shooting myself in the foot with GPU lanes because I want to SLI m.2 stuff.

If you have x99, then pcie won't be a problem, you will have more than enough.

 

If a board supports sli, the secod slot is off the cpu.

 

Running in pciex8 won't hurt performance in games.

[Zyndo]

3 hours ago, Electronics Wizardy said:

If you have x99, then pcie won't be a problem, you will have more than enough.

 

If a board supports sli, the secod slot is off the cpu.

 

Running in pciex8 won't hurt performance in games.

I don't think any of this answered my question. Thanks anyway though =). GL with the build OP, enjoy dat uber leet M.2 speed =)

[Sakkura]

10 hours ago, Zyndo said:

Would there be a way to predetermine this before purchasing a motherboard? Something on the spec sheet or in the manual that could give a definite answer? I'm considering going X99 on my next rig (or whatever the equivalent of X99 is at that point) and I want to do something like RAID 0 2 NVME m.2 drives (like a pair of Samsung 950's). But most motherboards that I tend to like, don't tend to come with 2 m.2 ports. If i end up doing SLI in that system, I don't want to be shooting myself in the foot with GPU lanes because I want to SLI m.2 stuff.

On X99 it's easy, just check if the lanes are PCIe 3.0 or 2.0. The X99 chipset is only offering 8 PCIe 2.0 lanes, where the CPU provides PCIe 3.0 lanes (28 or 40).

[Zyndo]

So even if I plug a Samsung 950 Pro 3.0x4 m.2 into the dedicated m.2 port on an X99 motherboard its still coming off my CPU lanes then? If its really as simple as that....

[Glenwing]

17 hours ago, Zyndo said:

Since we're here, I've often wondered. I'm aware the M.2 port comes off of the motherboard's chipset, but if I were to put in an PCIe adapter, and ran an M.2 card off of a PCIe port instead of the dedicated M.2 slot, does it then come out of my CPU's lanes? or is the hardware intelligent enough to still notice it as an M.2 drive and route it through the chipset lanes instead?

 

17 hours ago, Electronics Wizardy said:

Depends on the mobo.

No it doesn't. PCIe slots are hardwired to either the CPU or the chipset. The board can't dynamically decide that the lanes are now connected to somewhere else. You might as well be asking the motherboard to automatically plug your hard drive into a different SATA port.

 

If you plug a device into a slot which is wired to the CPU, it will use lanes from the CPU.

[Zyndo]

5 minutes ago, Glenwing said:

 

No it doesn't. PCIe slots are hardwired to either the CPU or the chipset. The board can't dynamically decide that the lanes are now connected to somewhere else. You might as well be asking the motherboard to automatically plug your hard drive into a different SATA port.

 

If you plug a device into a slot which is wired to the CPU, it will use lanes from the CPU.

That is what I assumed. now, how does one go about determining which PCIe ports are CPU driven and which ones are chipset driven?

[Glenwing]

8 minutes ago, Zyndo said:

That is what I assumed. now, how does one go about determining which PCIe ports are CPU driven and which ones are chipset driven?

In general, all motherboard tend to follow the same design. All ×16 and ×8 slots are from the CPU. ×4 slots (typically the bottom slot, and usually it's disguised as an ×16 slot) are usually from the chipset, but in some cases it's from the CPU. In earlier motherboard (Z77, Z87, Z97) you could tell because the CPU used PCIe 3.0 and the chipset used PCIe 2.0, so you could look at the PCIe revision of the slot. With Z170, both use PCIe 3.0, but the chipset has so many additional lanes (20, compared to the previous 8) that there's almost no reason to use CPU lanes, so it can be assumed that any ×4 slots on Z170 motherboards come from the chipset. Any peripheral connections such as M.2 slots, Thunderbolt ports, etc. come from the chipset as well.

[Zyndo]

Alright, thanks.

[Master Sonic Wisebeard]

19 hours ago, Zyndo said:

19 hours ago, Electronics Wizardy said:

Depends on the mobo.

Would there be a way to predetermine this before purchasing a motherboard? Something on the spec sheet or in the manual that could give a definite answer? I'm considering going X99 on my next rig (or whatever the equivalent of X99 is at that point) and I want to do something like RAID 0 2 NVME m.2 drives (like a pair of Samsung 950's). But most motherboards that I tend to like, don't tend to come with 2 m.2 ports. If i end up doing SLI in that system, I don't want to be shooting myself in the foot with GPU lanes because I want to SLI m.2 stuff.

 

I Believe this is the Motherboard you are looking for

 

http://www.newegg.ca/Product/Product.aspx?Item=N82E16813128878&nm_mc=BAC-GDR-CA-PC&cm_mmc=BAC-GDR-CA-PC-_-dyn-_-Motherboards+-+Intel-_-N82E16813128878&gclid=CI_P-JOY3c0CFVE0aQodjp0JHg

 

And here is a good info video of some guys who did what you want to do

 

 

Cheers

 

[Sakkura]

2 hours ago, Glenwing said:

 

No it doesn't. PCIe slots are hardwired to either the CPU or the chipset. The board can't dynamically decide that the lanes are now connected to somewhere else. You might as well be asking the motherboard to automatically plug your hard drive into a different SATA port.

 

If you plug a device into a slot which is wired to the CPU, it will use lanes from the CPU.

It does depend on the motherboard. Different boards will have different configurations.

2 hours ago, Zyndo said:

That is what I assumed. now, how does one go about determining which PCIe ports are CPU driven and which ones are chipset driven?

As I said, on X99 it's easy, you just check if the PCIe lanes are 2.0 or 3.0.

[Zyndo]

4 minutes ago, Master Sonic Wisebeard said:

I Believe this is the Motherboard you are looking for

Thanks, but I'm not interested in that board for a few reasons. Although seeing that video a while back is originally what sparked my interest in doing a build like this.

[Sakkura]

2 hours ago, Glenwing said:

In general, all motherboard tend to follow the same design. All ×16 and ×8 slots are from the CPU. ×4 slots (typically the bottom slot, and usually it's disguised as an ×16 slot) are usually from the chipset, but in some cases it's from the CPU. In earlier motherboard (Z77, Z87, Z97) you could tell because the CPU used PCIe 3.0 and the chipset used PCIe 2.0, so you could look at the PCIe revision of the slot. With Z170, both use PCIe 3.0, but the chipset has so many additional lanes (20, compared to the previous 8) that there's almost no reason to use CPU lanes, so it can be assumed that any ×4 slots on Z170 motherboards come from the chipset. Any peripheral connections such as M.2 slots, Thunderbolt ports, etc. come from the chipset as well.

No, you cannot assume that x4 slots on Z170 boards will come from the chipset. The lanes from the CPU can be split into an x8/x4/x4 configuration, most commonly for Crossfire, and many boards use that functionality. It makes sense to do it that way because while the chipset has tons of PCIe lanes available, it still only has a limited DMI 3.0 connection to the CPU, equivalent to a PCIe 3.0 x4 connection. So if you were to put a graphics card on there, bottlenecking would be a very real possibility.

[done12many2]

1 hour ago, Master Sonic Wisebeard said:

 

I Believe this is the Motherboard you are looking for

 

http://www.newegg.ca/Product/Product.aspx?Item=N82E16813128878&nm_mc=BAC-GDR-CA-PC&cm_mmc=BAC-GDR-CA-PC-_-dyn-_-Motherboards+-+Intel-_-N82E16813128878&gclid=CI_P-JOY3c0CFVE0aQodjp0JHg

 

And here is a good info video of some guys who did what you want to do

 

 

Cheers

 

 

The problem with running a RAID 0 with M.2 through a z170's chipset is that you saturate DMI 3.0 with 2 x M.2's let alone 3.  You'll still see improvements in overall performance by the sheer fact that you are using 3 x M.2 drives, but sustained read and writes will be substantially limited to around 3 GB/s both ways.  That's a big hit when you consider that 2 x 950 Pro 512 GB M.2s can do 5 GB/s read and 3 GB/s write by themselves if you split them between the chipset and CPU lanes.  3 of them would be 7 GB/s + read and 4.5 GB/s write via a CPU / chipset lane split.