Mental Ray Single Frame taking 20 hours?!?

#1

First off, apologies, I am very new, with only a year under my belt with Maya and Mental Ray.

I’ve been working on rendering a single frame in 1080p with 5 or 6 render passes, AO, diffuse etc. With unified sampling set to quality of 1 in Maya/Mental Ray, it’s taking 20 hours to render one frame! And I have a 300 frame animation ahead of me.

I realize it’s hard to discuss a specific scene without a file but I’ve attached an AO pass of the scene that shows that the geometry is fairly complex. The scene also includes a couple of lights tied to Mental Ray fog volumetric node so not sure if that’s a thing. And it’s fully textured with textures up to 2K. Sadly I don’t have a frame handy to show this.

This AM I quickly fired off a 520p test at 0.1 quality and the whole frame was complete in ten minutes. Should there really be a 20 hour difference between 0.1 quality at 520p and 1 quality at 1080p? This seems crazy.

Running a dual quad core Xeon 3.0 Mac Pro with all 8 cores confirmed as operational and a memory limit of 6Gb.

Any input is much appreciated to this noob. Frankly I have no idea what I should expect it to take for a single frame like this, but the difference seems insane.

Here’s a link to the AO frame:
https://www.facebook.com/paulchambers3d/photos/a.406792049471935.1073741832.403497396468067/425827337568406/?l=e460a9f8d3

Many, many thanks in advance,

Paul

#2

Well. I found the issue. It was the Parti-Volume I had covering the scene with about 8 lights linked in for a fog effect. At the default sample step values of 0.1 the render was taking 20+ hours. Adjusting these to a 1 or higher dropper the render down to 2 hours with no real loss in quality. Man, that’s an expensive effect.