So at work today, I came across an issue with Maya 2012’s Mental Ray renderer. Scenes had fairly low settings and rendered quickly in the Maya frame buffer, but were rendering SLOW at batch render time. In fact, only 8 out of 16 threads (or less) were being utilized.
As it turns out, the Mental Ray Batch Render Option screen has a refresh issue. Watch your PC Task Manager “Performance” tab carefully. If Mental Ray isn’t using every core at close to 100% capacity, unselect Auto Render Threads and manually type in the number of render threads. I also recommend turning Auto Tiling off and changing the task size to 16 (i.e. 16×16 pixel buckets). Your render times should go down significantly.
Be aware that occasionally Mental Ray will ignore your manually entered values. Just delete them and retype the values, then press Enter. Should work like a charm. I typically click on “Batch Render” from the option menu rather than “Batch Render and Close” just to be safe.