Is filling up the PCI-E on skylake even worth the efford?

Renegate · September 9, 2016

Before i start allow me to introduce you with the PC hardware i wanted to buy as my new workstation.

Motherboard: Asus z170 ws

CPU: INTEL 6700K

DRIVE: SAMSUNG SSD 951 SM (m.2)

RAM: 32GB DDR4 3000MHz

VGA 1: Asus gtx 970 strix (from previous pc)

VGA 2: an under 100 dollar vga just for the 2 extra monitors

Network: asus 10Gb ethernet card

Now let me explain my problem. After going through some research i discovered that the pci-e 3 and pci-e 2 lanes on the ws z170 would bearly be enough to handle everything. As follows:

Pci-e 3 lanes

16x gtx 970

8x vga no2

Pci-e 2 lanes

4x 10Gbps ethernet card

The m.2 as the support of Asus claims doesn't use the pci-e lanes but intead it uses the sata controllers bandwith at the expense of the nvme features. But the tech devision that aparently my ticket was send never confirmed it.

And now my questions:

1) Is the above scenario even possible?

2) If i put another m.2 in a raid 0 and make a file transfer over the network of my NAS that also has 10GB ethernet connection and can utilize it to it's full potential. And while that file is been transfer i download torrents and game at the same pc with none cpu demanding game just to stress some bandwith of the pci lanes and the cpu a bit. Will the 6700k be able to handle this traffic?

1 large file transfer, 1 torrent download with 20mbps and some gaming would be enough traffic for the 6700k to be the bottleneck in this case?

bgibbz · September 9, 2016

You are fine. M.2 drives use motherboard pcie lanes eager than CPU lanes. Either way, the second gpu should be unnecessary. The gtx 970 has 4 outputs.

manikyath · September 9, 2016

how many monitors do you have?

my gtx970 does perfectly fine driving a 4K panel, a 1400p panel, and a 1080p panel.

Sakkura · September 9, 2016

First, it's worth bearing in mind that the Z170 chipset has up to 20 PCIe 3.0 lanes available, in addition to the 16 PCIe 3.0 lanes from the CPU.

Now, as far as I can tell, what the Asus Z170-WS board does is use the 16 CPU lanes for the 4 main PCIe slots. They use a PLX chip to basically double the PCIe lanes from the CPU, to 32.

If you put the graphics cards and the 10Gbit ethernet card in three of the main PCIe slots, the first card will have 16 PCIe 3.0 lanes, and the other two will have 8 lanes each. That should be perfectly fine.

The PCIe lanes from the chipset are used for all the other ports and slots. So the M.2 slots have plenty of PCIe lanes available.

So...

1. Yes

2. The link through the chipset is limited by the bandwidth of the DMI 3.0 connection to the CPU. That's just under 4GB/s in theory. If you RAID0 a couple of fast M.2 NVMe drives, they would in theory be capable of speeds up to around 5GB/s in some situations. So the chipset would bottleneck that a bit. But 5GB/s is already way more than a 10Gbit ethernet connection can handle. Even if you're saturating a 10Gbit internet connection with torrents, that's "only" 1.25 GB/s. The system can handle that just fine. And if you're gaming, the communication between the CPU and graphics card happens across separate PCIe lanes, so that's not affected.