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I did a little research and found out that my Abit IP35 Pro motherboard supports ATI's crossfire but not nvidia's SLI. However I believe there may be a workaround to get two Nvidia cards on my particular motherboard. There is a catch in that I would only get x16 and x4 performance because of the way the motherboard was designed.

I might have to resort to only one card unless anyone knows a workaround for my situation. So honestly, how bad is Octane performance with only one video card? Is it considered a necessity or a luxury to have two?

Octane doesnt make use of SLI so you dont need to worry about it.
Its a really good idea to use a basic card for the UI display and a grunt one(s) dedicated to cuda rendering only - no monitors connected.
Even though the other slot you have is 4x that would be 'ok' - it will just take a little longer to load your scene prior to rendering. Some mobo allow you to set which is the primary pci-e slot in the bios so it could be that you could run your cuda card in the 16x slot anyway.

I use a motherboard that supports crossfire and not SLI. As pixelrush says, it doesn't matter.

Best idea is to put your main display on one card and a secondary display on your "grunt" rendering card. I bought a 23" HD display for $130 as a main display and use an old SVGA as a second display.

For normal use, I get the pleasure and productivity of two displays (a huge help for modo, ArchiCAD, Revit etc.), and when I'm running Octane (displayed on the main display, computing on second "grunt" gpu), I ignore the second display, which predictably becomes very slow.

I think the latest Nvidia drivers also do a slightly better job of sharing resources: I can use the secondary display even when rendering, but I keep it for things like the EVGA Precision app (temperature / fan control mainly).

Also, I have my Quadro FX 580 in the 16x slot for fast interactive graphics, and the GTS 470 in a 4x slot (it only affects model load times, not rendering times).

Does that make sense?

so what's the benefit of having 2 cards instead of one, besides the dual monitor option?
Can't I use them both for rendering?

aygung wrote:so what's the benefit of having 2 cards instead of one, besides the dual monitor option?
Can't I use them both for rendering?

yes you can. (use them both for rendering) if they're GTX400 series you'll get near linear speedup eg 1.9x
maybe reread the posts above for the rest of the details, all the info is in this thread.

Radiance

I was leaning towards 2 gtx 460s, as I read they are really good cards and best performance for the money.
I read your posts yesterday and you keep saying 2gb of ram so I'll buy them with 2 gb of ram now.

I was just about to build a powerhorse workstation with 2 6core xeons and stuff a month ago and I saw this new gpu rendering tech. all my plans have changed... now I think I wont need this much cores but I'll need a second monitor.. am I right??

aygung wrote:... but I'll need a second monitor.. am I right??

Only if your workflow demands it. You don't need two monitors becouse you'll have two cards

Here's a diagram - maybe it helps

Thanks for the replies everyone.

@pixelrush
Thanks for the helpful diagram. I have a Corsair 620HX power supply unit so hopefully it will be good enough to power a GTX 460 or maybe a GTX 470. I know my Quadro FX 1500 doesn't need a separate power plug so I'm good there. My plan is to use the Quadro for 3dsmax/maya/blender and the new GTX 460/470 in the second x16 slot for Zbrush, Photoshop and Octane. As I mentioned earlier the second x16 slot goes down to x4 performance for my particular motherboard. Hopefully there isn't a huge performance hit.

@aygung
I was also looking at a dual xeon workstation too until I saw great renders from Octane, FurryBall, MachStudio Pro, Luxrender, Indigo Renderer, etc.

Off topic: Can anyone here remark about the loudness of a GTX 470 at around 60-70% fan speed? Maybe compare it to something like an old Xbox 360.

pixelrush wrote:Here's a diagram - maybe it helps

that's one really good image. very helpful.
would you mind if we add it to our manual ?
(and maybe post it in the resources forum )

Radiance