When rendering in mental ray for Maya, you can generate shadow maps. You can use a standard shadow map, or a detail shadow map.
The standard shadow map takes fewer samples than the detail shadow map, so they require more resolution. Detail shadow maps use shadow shaders at intersection points with the shadow-casting objects. They take more samples per pixel, and therefore, require less resolution. Detail shadow maps take extra attributes into account that regular shadow maps do not, such as refraction, reflection, and transparency settings on objects. While detail shadow maps may take longer to calculate than standard shadow maps, they are more efficient than raytraced shadows for motion blurred shadows.
To turn on shadow maps for mental ray, see Work with mental ray shadow maps.
You can use detail shadow maps on a per-light basis (for point lights, spot lights, and directional lights). Detail shadow maps are saved as tile-based files. New tiles are dynamically added to the file, if there are lighting and shadow changes, when you render new frames. Because detail shadow maps store more per-pixel information, file sizes are larger than standard shadow map files.
Detail shadow maps take extra attributes into account that regular shadow maps do not, such as refraction, reflection, and transparency settings on objects.
The new attributes can be found in the Attribute Editor on the light’s shape node, in the mental ray > Shadows > Detail Shadow Map Attributes section.