pci-e sli question on z97

bipolarbear · 23 Jul 2015 at 10:53

Hi, I've got a Gigabyte Z97X-Gaming 7 motherboard with 2 GTX780's in SLI, both running at x8. I purchased a dual nic Intel Pro/1000PT server card with the intention or bonding the connnections to my netgear smart switch. This card has a pci-e x4 connector. I inserted the card into the one remaining pcie x4 slot, the second GTX780 then dropped its speed to x4 and I lost SLI. I checked the motherboard manual and this is documented behaviour, there doesnt seem to be a way to manually configure the second gfx card to x8 when there's something in the bottom slot.

Just wondering is this something peculiar to this motherboard? or it is a chipset/z97 thing? should i be looking at a different motherboard or chipset?

thanks!

edit: apparently one way is to cut/mod one of the pci-e x1 slots so it can take a x4 card - just dremel out the notch at the end - and it *may* work depending on the card.... worth a shot maybe.

zola25 · 23 Jul 2015 at 21:10

It's just how your particular model of board shares resources. My Z97X-UD3H-BK's PCIEX4 slot shares bandwidth with the x1 slots. I run my 2 x GTX 980's at 8x/8x and can still use the X4 slot. Checking the manual for your board though definitely confirms it behaves differently, just as you said.

If it was me, I'd not risk damaging the board and/or losing the warranty on the off chance the NIC might work. Even if it did work, wouldn't running it in 1x slot cripple the bandwidth?

I'd see the options as follows...

1. Not use the NIC card
2. Change motherboard to one that shares PCI-e resources differently
3. Sell the GTX 780s and replace with a single GTX 980Ti that can run at x16 in one slot, freeing the x4 slot for your NIC

bipolarbear · 24 Jul 2015 at 09:12

Too late - I did it, and it works lol...

I think pci-e x1 has more than enough bandwidth for 2 gigabit ports, a quad would be pushing it though i think.

Strange that the UD3H is different to the Gaming-7 in that respect though, I wouldn't have thought there was much between them feature-wise.

Unrelated question - is a single 980Ti faster than my 2 EVGA 780 Hydro Coppers in SLI?

zola25 · 24 Jul 2015 at 10:01

My guess is that on the Gaming 7 the PCI-e lanes for the longer slots are all connected to the CPU, possibly in order to support 3 way Crossfire? On the UD3H the first two long slots are connected to the CPU with the X4 slot connected to the Z97 chipset.

As for 780 SLI vs. a single 980Ti, most benches put 780 SLI slightly ahead when scaling is working effectively. 980Ti would give similar performance but without any of the drawbacks of SLI, which are admittedly few of late in my experience. IMO it would only be worth the change if you were desperate to release the second PCI-e slot or were running into VRAM limitations.

Meaker · 26 Jul 2015 at 21:54

You get 16 Gen 3 lanes from the CPU and 4x Gen 2 lanes from the southbridge. It is just a different way of sharing things out.

You get 500MB/sec out of a single PCI-E 2.0 lane so even quad gigabit should be fine with overheads.

C64 · 26 Jul 2015 at 22:45

Can I ask why not use the onboard lan ?

bipolarbear · 27 Jul 2015 at 11:03

I'm teaming the 2 intel interfaces into one 2Gb bonded interface via 802.3ad link aggregration. Interestingly the Intel software gives me the option to include the onboard interface in the team even though its a realtec adapter... but I'm not sure how well that would work so i have left it out. 2 interfaces is enough anyway.

Confused Stu · 27 Jul 2015 at 15:04

Bit late to the party, I know, but this behaviour was the reason I went for the Z97X-Gaming 5 over the Gaming 7. The coolers on my GPUs block out most slots, so I have to put my soundcard in the lowest PCI-E slot as it's the only one unblocked. On the Gaming 7 this slot is fed with PCI-E3 from the CPU, so my GPUs would have dropped to 8x/4x. On the Gaming 5, this slot is fed from the motherboard chipset with PCI-E2, but it leaves the GPUs still running at 8x\8x.

It's just annoying this can't be configured in the BIOS/hardware switches so you have to know what configuration you'll have over the coming years when you buy the motherboard, rather than being able to configure it the best way for your current setup no matter how it changes.