Anyone who runs multiple nVidia cards on risers?
I am looking into running 5-6 cards per rig, but i think someone earlier in this thread mentioned that cudaMiner still has some trouble with high traffic so that risers could be a problem. (1x to 16x risers, 5 or 6 per rig)
I notice a severe slowdown from 340 khash to ~280 khash when going to a 1 to 16 riser, I was able to recover some speed at the suggestion of Christian to use the -H 2 switch which got me back up to the 320 khash level, but nothing I can do gets me back to 340. I will be getting 16 to 16 risers in tomorrow for testing this weekend. Not sure if anyone has done any serious testing of the 1 to 16 risers with NVidia cards and cudaminer, I will try with the cards I have (750 Ti, 680, 780 Ti) but it will have to wait till this weekend. I will post what I find. If anyone has any special requests, just post 'em here. I also have a motherboard with 4 x1 and 3 x16 slots coming in tomorrow.
I'm running into the same issue.
Setup:
Intel Pentium G3220
Asus Z78-Pro
4GB RAM
1kW Seasonic Modular PSU
7x x1-x16 Riser Assemblies
2x Zotac 750 Ti, Reference
5x ASUS 750 Ti, OC
So far I've only messed with the Zotac reference cards.
I have OC'd CPU+135,VRAM+700; Modified VBIOS to lift TDP limit.
On x16 slot, 320-330 kH/s (with -H 2 flag). On x1-x16 riser assembly, ~280kH (with -H 1 flag).
-H2 flag using x1 riser causes unusually low performance. I believe this is due to the fact that for the CPU to offload the GPU, the data bandwidth required for the offload traffic is saturating the x1 bandwidth, thus artificially limiting the card. I suspect that even with -H2, we're seeing some limitations relating to either the way cudaminer works or the x1 bandwidth limitation.
My theory is that the only fix for a riser use-case is to utilize x16-x16 riser assemblies. Otherwise, you're throwing away ~50kH/s per card attached to a x1 riser. As an electrical design engineer, this hurts me.
