Refraction ray depth is the number of times a ray will be refracted. Diffuse ray depth will increment the light rays bouncing around in the scene. However, this will also lead to longer render times. Using Ray Depth for interior rooms and areas is recommended.

Some solid base-lines for samples to use are: AA = 7-11, Diffuse = 2, Glossy = 2, Refraction = 2, SSS =2. If the camera's AA samples equal 4, then the total samples will equal 16. The actual number of samples, is the square of the input value. The more samples the better, but the longer the render time.

Make sure your Arnold Plugin is turned on, otherwise it will not appear in Maya. If you would like to read more on Arnold visit the Arnold render guide: HERE. Hopefully this help you render your VFX and scene more effectively. We'll talk about some ticks you can use while rendering in Arnold, and also how to diagnose for errors and aliasing.

Arnold is a hugely useful render engine, and in Maya it's been implemented as one of the main ones.

Ai standard surface maya