Help choosing GPU

[kalinaraicheva]

I hesitate between GTX 770 2GB and 4GB for 3ds max landscape scenes - do I need more VRAM and what exactly does the VRAM - will it improve the rendering time or the viewport speed - the differences in price is not that much but some says that when it comes time to use it, the GPU will be so slowly that I will have to change it because it`s 256 bit. Also what do you think about two GPUs x 2GB - as far as I know it does not improve the rendering time by 100% (/2) but about 70% and it`s better not to use them is SLI when rendering, but will a two GPUs in SLI mode improve the viewport speed?

Thanks in advance!

[Dimitris Tolios]

GPU rendering requires alot of VRAM as for GPU accelerated renderers to work with them, they have to load 100% of the geometry, scene assets (XRefed geomery, proxies, material maps etc) into each card to be utilized. Thing of each card as a rendering node that works independently of the other, and the main system memory.

 

The 256bit paging of more than 2GB of VRAM is an issue with games, not GPU renderers. Games need to access to large packages of data simultaneously for each frame. GPU renderers are not that limited by VRam bandwidth or paging, but unlike games which run a bit slower when VRam is not enough, GPU renderers simply don't run at all. Games keep exchanging information between the CPU - Main RAM - GPU all the time, flushing the VRam and reloading textures on demand, while GPU rendering needs to be loaded and run 100% on each of the participating GPUs for the duration of the compute.

 

Thus it is better to be safe than sorry with them. 4GB 256bit bus cards are a gimmick unless you Tri-SLI or something crazy like that and/or use surround monitors (i.e. 3x 1080p or more). Only modified games with 4K textures like Skyrim even break 2GB of usage.

 

SLI has no effect on GPU rendering. SLI physically links and coordinates two or more cards so that a scene can be equally split between them.

 

GPU rendering doesn't care about your cards being identical or not, having the same memory or being the same models. You can mix and match w/e you want. SLI won't harm it, but won't have any difference in performance.

 

SLI also is not supported by most 3D CAD programs - will be useless for most viewports outside games.

 

I believe 2x identical GPUs will have more than 70% increase in speed under ideal conditions, perhaps not 100% faster, but closer to that than not.