Skylake PCI Bus Saturation?

[eTanium]

So, I'm looking to build a new system. I want RAID 0 some M.2 SSD's, but I want to ensure that my Processor and Motherboard will have enough PCI lanes for them, and the SLI video cards. I've been researching this a lot (hours and hours), but I am still a bit confused, and wanted to see if anyone had some solid advice/answers.

PC Parts: (note, only one 1080 listed, as I already have one).
https://pcpartpicker.com/list/rWQwm8

So, I was mainly looking for a Mobo that had dual M.2 slots, which the Gigabyte GA-Z170X-Gami​ng 7, has, but I then learned that the two PCIe 3.0 lanes will downplay town 8x by 8X in SLI. I hear this doesn't really degrade performance, as the two 1080's can't fully saturate those 16 lanes anyway (or no?). If anyone has suggestions on a Mobo that runs SLI in 16x by 16x and still has two M.2 slots, please let me know.

So, that's 16 lanes down. Now, with two M.2 drives, which each run at 4x, that's 24 lanes. What lanes does the GA7 Mobo use for the graphics cards, and which for the M.2's? I've read that the M.2s are running on the PCH? This is separate from the graphic PCI bus, correct?

Essentially, I don't want the two M.2's and the two graphics cards fighting for direct PCI lanes to the cpu.

Any thoughts/info/advice is much appreciated. I am going blind researching this.


Thanks!

 

[Rogue Leader]

The M.2 slots on the motherboard do not use CPU PCIe lanes.

The 6700k processor has 16 PCIe lanes that it shares amongst the 3 GPU slots on your motherboard. So when you SLI your 1080's you will be running them at x8/x8.

The M.2 slots and any other PCIe slots and other system devices use the 20 PCH PCIe lanes of the Z170 chipset. You'll notice the M.2 slots share lanes with the SATA express ports, so if you use them those ports are disabled (which who really cares SATA express drives are non-existent).

In short you have no crossing over to worry about. The only thing I would say is running RAID 0 on M.2 drives is a waste of time and money.

http://www.tomshardware.com/reviews/samsung-950-pro-256gb-raid-report,4449.html

Looks cool in benchmarks, no real world performance benefits.

 

[ahnilated]

I can attest to there being no real world gains in running M2 drives in raid 0. In fact in a lot of ways it will be slower, which you probably still wouldn't notice being how fast they are. The big deal is you increase your failure ratio by having 2 drives instead of 1.

 

[eTanium]

The 6700k only has 16 PCIe total? So, even if I found a board that allowed for dual PCIe 16x, the SLI cards would still run 8x by 8x?

Also, I don't care about losing SATA lanes on the PCH because I don't plan on using any additional storage; I have a NAS for that.

The provided RAID link was usefully. Raid or not, the M.2 will be a noticeable difference from my existing SATA SSD.

I was running my assumptions off of this video, but they are only benchmarking. Still, seems to be some benifit of the RAID, for at least two cards:
https://www.youtube.com/watch?v=9dA8yNEZgQU

 

[Rogue Leader]

The 6700k only has 16 PCIe total? So, even if I found a board that allowed for dual PCIe 16x, the SLI cards would still run 8x by 8x?

Also, I don't care about losing SATA lanes on the PCH because I don't plan on using any additional storage; I have a NAS for that.

The provided RAID link was usefully. Raid or not, the M.2 will be a noticeable difference from my existing SATA SSD.

I was running my assumptions off of this video, but they are only benchmarking. Still, seems to be some benifit of the RAID, for at least two cards:
https://www.youtube.com/watch?v=9dA8yNEZgQU

There is no such Z170 board. While it may have 2 or 3 (or 4) x16 slots, they run only at x8 when in SLI (or if you try to do something like quad crossfire they even run as low as x4) because the CPU only has 16 lanes.

You have to move to X99 and get a 40 lane CPU to get true x16/x16 SLI. Honestly the performance difference in minimal, and the 6700k is faster when it comes to gaming workloads.

As for RAID, like I said (and the article I linked agrees), it does benchmark faster, but real world there is no difference, meanwhile you add complication and another avenue for failure. And I trust Tom's results over some youtube channel.

 

[eTanium]

I'm aiming to push 4k resolution, at max settings for current titles. I haven't had an issue doing so with the 1080 on 1080p. I have seen that an pair SLI of 1080s was able to do this. I imagine that some settings would need to be scaled back in the coming years...

I imagine, even since the cards will be 'downgraded' to 8x by 8x, the SLI configuration will still perform better than the single 1080 running at 16x? I don't expect a two fold increase or anything, but still better than the single.

I've always wanted to SLI, but I've never gotten around to it. I've always run single GPUs, and my 680, overclocked, has been doing the trick, up until now. Yet, with 4k, and resolutions on the rise, I think it is time to drop some cash for SLI.

 

[Rogue Leader]

I'm aiming to push 4k resolution, at max settings for current titles. I haven't had an issue doing so with the 1080 on 1080p. I have seen that an pair SLI of 1080s was able to do this. I imagine that some settings would need to be scaled back in the coming years...

I imagine, even since the cards will be 'downgraded' to 8x by 8x, the SLI configuration will still perform better than the single 1080 running at 16x? I don't expect a two fold increase or anything, but still better than the single.

I've always wanted to SLI, but I've never gotten around to it. I've always run single GPUs, and my 680, overclocked, has been doing the trick, up until now. Yet, with 4k, and resolutions on the rise, I think it is time to drop some cash for SLI.

Depending on the game SLI can be up to an 80% or so performance increase. As for x8/x8 vs x16/x16 the performance difference between those speeds is less than 5% (I used to have a link to back this up but I can't seem to find it right now), in other words in titles that support SLI you will have no problem getting a huge performance bump out of a second 1080.

 

[eTanium]

Thanks for the info guys. I'll adjust my build accordingly!