3 GPUs: how to specify second slot for the display?

[ooofest]

(also posted at tomshardware, but got no takers)

Hi Folks,

I have an ASUS Z8-WS motherboard with its first three PCI-E slots occupied by GPUs: I would like the weakest card (ASUS Strix 970) to drive my monitor and the other two (Titan X (Pascal)) to be used for 3D rendering engines.

If the 970 is in the first PCI-E slot, one of the Titans won't show up in Windows (but is visible in BIOS). That's weird, so I tried putting the 970 into the second slot.

If the 970 is in the 2nd GPU slot, Windows can see all three cards but the monitor doesn't register a signal from the 2nd GPU slot card - only from the first GPU slot!

Each card can drive the monitor fine if in the first GPU slot, BTW.

I don't see how to configure the ASUS BIOS or GPU Tweak II utility to have this motherboard use the second GPU as the lone monitor.

[1mluer]

How about just connecting your monitor to the 2nd card and use it's output to drive your monitor ? I am not sure of the question here? Love to help but don't want to commit to much yet.

I may be reading this wrong ..

[ooofest]

1mluer wrote:
How about just connecting your monitor to the 2nd card and use it's output to drive your monitor ? I am not sure of the question here? Love to help but don't want to commit to much yet.

I may be reading this wrong ..

Thanks, I just reworded the original post to hopefully be more clear!

So, that's what I tried: just connect the monitor to the 2nd GPU. Unfortunately, it never registered a signal with the monitor. Any of these cards work fine with the monitor if in the first slot, but apparently not from the second slot.

And, if I switch the cards so the ASUS Strix 970 is in the first slot, then one of the Titans doesn't even show up in Windows (but is still visible in the BIOS). So, this all seems kind of weird.

When I enable the iGPU (Intel 4600) in the BIOS, that works fine with the monitor, too.

My main goal is to use the 970 as my daily driver and the Titan cards for rendering.

So, I'm wondering if there's a specific limitation on this ASUS motherboard for the 2nd GPU slot to be used for the monitor.

[xeromist]

Do all 3 cards run your rendering tasks correctly? It's weird that slot arrangement makes one of your cards disappear. Makes me wonder if the card in the 2nd slot is even functioning correctly.

[ooofest]

xeromist wrote:
Do all 3 cards run your rendering tasks correctly? It's weird that slot arrangement makes one of your cards disappear. Makes me wonder if the card in the 2nd slot is even functioning correctly.

Yes, right now I have them ordered as:

(PCIEX16_1) Titan X
(PCIEX16_2) GTX-970
(PCIEX16_3) Titan X

and all three are available in Windows, plus all three can be used to render in Blender Cycles, Octane, Iray, etc.

Hm, your question makes me think I should test trying to drive the monitor from slot 3, too - I'll check that out and post an update.

[ooofest]

The issue has somehow been fixed to my satisfaction!

I swapped the STRIX GTX-970 with a different STRIX GTX-970 and placed that in PCI-E Slot 1. The two Titan X (Pascal) cards went in PCI-E slots 2 and 3.

In the UEFI/BIOS, I set the system to only use the PCI-E card(s) and changed the connection with the GTX-970 to use its DisplayPort.

Magically, this combination of changes has worked: the Slot 1 GTX-970 is driving my display, while all three cards are available to Iray, Octane and other renderers for processing.