If your scene contains particles, the way you render your scene depends on the type of particles it contains. There are two main types of particles: hardware particles and software particles.
For more information on setting particle render types, see Choose how particles render.
Click the image below to play an animation showing a software-rendered particle cloud.
Rendering particles in mental ray for Maya
You can also render the following particle types with mental ray: Points, MultiPoint, Spheres, Sprites, Streak, MultiStreak. The implementation builds on a geometry shader that creates actual geometry from per-particle data which is then passed on to mental ray for rendering.
Hardware particles are shaded in a way that is similar to software particles: a shading group must be assigned to the particle shape, and its surface shader completely determines the appearance of the particles. This implies that none of the shading-related attributes are supported when rendering hardware particles with mental ray.
Motion blur is supported for hardware particle rendering in mental ray.
spriteNumPP is unsupported; therefore, assigning different sprites on a per-particle basis is impossible. mental ray and Maya Hardware may render particles slightly differently.
Using custom mental ray shaders with particles
If you are using custom mental ray shaders that work with particles and want to access the particle user data, see InternParticleData.txt and InternParticleExample.txt in the devkit in the following directory for more information: mentalray/devkit/docs/writingShaders.