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What are the advantages of turning on cache BVH for a cycles render?

Not sure how to elaborate. I'm not necessarily looking for a technical description, just a better idea for when to use it, and when it's not worth the disk space.

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    $\begingroup$ Note that BVH caching was removed in Oct 2015 as it was no longer useful. $\endgroup$ – Greg Zaal Jul 29 '16 at 15:55
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From the 2.62 release notes -

For renders where only the camera or materials are changing, while meshes stay fixed, it is now possible to skip the sometimes slow BVH step, by enabling BVH Cache in the Performance panel. This will store the BVH on disk for subsequent (animation) renders of the same scene. Note that if the scene does change in the animation, enabling this option will make rendering somewhat slower.

Times when it will help -

  • Test rendering one frame while you adjust materials.
  • A camera flying through a static scene

Times when it will not help -

  • Any mesh changes during an animation (shapekeys or armature)
  • Any object movement during an animation
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Turn it on when you want faster test renders. Especially if you are making mostly lighting or material changes. The problem arises when you are rendering a large animation. I always think of cache (in a general sense) as more of a memory thing, and less of a disk space thing. Well, blender is caching it to disk. And it's huge, and if you leave it on during an animation you will run out of disk space. Quickly.

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