Multiple GPUs on Asus Z-97P

[Blizz]

Hello, im going to buy a GTX 1080, i feel bad at selling my GTX 970, that GPU worked hard for me. <3
The Z-97P doesn't support SLI, but for Octane u need no SLI if i heard it right.

Can i work with 2 GPUs on this Mainboard? And if yes, is there a performance loss?
Sorry if my english is bad, thx for the help guys!

[itou31]

Hi,
You can do dual GPU, but the second slot is only x2 PCI lanes. So you would expect some performance loss :
- on first transfer before rendering
- Frame buffer on RAM (since V3)
- on OOC feature (Texture and geometry on V4)

I experience this with setting 1x, and also test with different PCIe Speed (x2, x4 and x8). No differenve on x8, slight loss on x4.
And I conclude that the network is better comparing between (2PC with 4GPUs (8x PCIe) is better than 1PC with 8GPUs (8x on 4GPU and x1 on 4GPUs), but need 2 licences !)

[Blizz]

Thank you very much for the help!
Im pretty new to stuff like this, i would be happy if u can answer me some more questions.
- Is the performance loss high? It should only affect the GTX 970 if i think right?
I have 3 options:
- Sell the GTX 970 and only use the 1080.
- Buy a new psu and use the 1080 with the GTX 970.
- Buy also a new Mainboard, so i would have no performance loss. (But is that really a good idea, to spend another ~80€ for a mainboard, just for the new slots?)

Thank you very much!

[itou31]

Hi,
- I don't remember exactly, but it's about 6 to 10%, depending of the scene on 2x PCIe (your second slot). The performance loss will not affect the rendering process, but only transfer from VRAM to RAM. So, I cannot say for the 970, I have test this with titan1.
- You can keep the 970, it could help the rendering. Each card will render at its speed. But I remember that on one of my test with 4 titans (3 on 8x and with one on the 1x), and the performance is not so significant than 3 titans only on 8x, but it depends on the scene.
- option 2 and 3 still need a new PSU.
- and also, the 970 has only 4GB, so if use with 1080, you're limited to only 4GB.

[Blizz]

Thank you very much for the help!
I hope the impact from the crappy GTX 970 Vram is not too big, but i think i keep it.