Hello,
I’m running 2.67 on a PC, and I’d like to pair a 2nd GPU with my current Nvidia GTX570(1.25GB). Are there any rules for pairing GPUs? Am I limited to another GTX570 with the same ram amount (1.25), or can I go with something faster?
Thanks in advance!
Windows 7
i7-2600k @ 3.4GHz
16 GB ram
Cycles should be able to use both cards, but just be careful of your PSU usage…
cycles will be limited by the lowest card amount of ram, adding a second GPU will only speed the rendering up, it does not help with the ram usage… say your second GPU is a 3GB card… if you want to use both at the same time, you still will be limited to 1.25GB… if you choose just to use your new card, well then it the ram limit will be upped to 3GB…
Why is it like this for ram usage you ask? well… The entire scene needs to be stored on all rendering devices entirely… you can transfer data between devices but its slow. very slow. so to get decent rendering speeds it needs to reside on both cards.
No problems at all. I’m running a GTX 570 together with a GTX480, and besides the vRAM usage that doublebishop mentions it’s a nice addition. My rendering speeds arent that far from a single Titan.
Another great thing is that when I’m not rendering, I only used the 480 for rendering. Then the 570 is the main card and handles all the UI stuff, while the 480 renders the stuff in the 3D viewport. So now I can work without hiccups even when the 480 is rendering, where I would get lag when I only had one card.
Thanks! I’m trying to decide between adding a 580 or simply dropping in another 570 with the same specs. Am I wrong in thinking the difference in rendering times might not be all that significant for 2x570 vs 570 + 580?
i believe the 580 is about 20% faster then the 570… and also has the extra ram… but you have to remember that you already have one 570 in your machine, so instead of the difference being between 100% and 120%, its 200% and 220%, so it may only make a difference of 10%… moreover, with dual gpu rendering, one card is usually idle by the end of the render waiting for the other card to finish (one card per tile is how its allocated)… which means that in a balanced scene… the gtx 580 will end up finishing first and being idle for a little while.
when using two of the same card, can they be SLI connected or do they need to stay separate?
Here are some results of my cards for you from the archvis benchmark file.
GTX 480 02:38
GTX 570 03:09
Both 01:30
And a 580 is even faster than my old 480 
Morgoth: They should not be bridged for optimal performance.