Aggregate Volumes can decrease the render time for volumes by combining them into a single structure for the renderer to process.  To get started with aggregate volumes in RfKRfH, there are two steps: setting the aggregate name on the volume primitives geometries and specifying a matching aggregate name in the integrator.

...

You may instead want to specify volume aggregates on the Geometry level. To do this, you will need to add a primitive attribute called ri_volume_aggregate.  If ri_volume_aggregate is set as both an object parameter and a geometry attribute, the geometry attribute value will be used.

Image Added

There are no custom tools for setting up volume aggregates in Solaris. You must add the setting with the Geometry Render Setting LOP. 

...