volume very slow rendering, just a very simple vdb sphere

[len_xie]

it's a simple vdb created from vdb from polygon , I know volume could be slow, but not this much.
after ligth cache finished computing, it takes very long time to proceed for actual rendering, did I do anything wrong , or this is vray speed for volume.
the vdb only 10MB in memory, with 2 vray lights.
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houdini 19.5.5.551 windows 10,V-Ray for Houdini number:22320, cpu mode

[chakarov]

Hi len_xie, the slow down is caused by reducing volume density ( "scale" parameter in Smoke tab of the shader ) which allows light to penetrate deep in the volume. In order to reduce render time you could try tweak "Step" and "Shadow Step" parameters in Rendering tab of VolumeGrid Shader.

[len_xie]

@chakarov hi, I tried to increase step and shadow step to maximum value but it's the same, but I found that by turning off Probabilistic Volumetrics, can improve a lot.

[ronald_a]

len_xie try upgrading to a new build. There habe been issues with volume rendering speed that have been adressed not too long ago.