Disable Animation Detection
Mental Ray automatically detects animation of scene objects and related shading nodes when translating subsequent frames. The Optimize Animation Detection option (in the Render Settings window, mental ray tabs, in the Options tab, Translation section, Performance sub-section) even performs a pre-scan of the Maya dependency graph to find animated nodes much faster and to mark the individual nodes accordingly for accelerated translation of the whole animation.
Usually you can safely disable this if you see your animation renders are taking much longer than expected. However, like most things this depends greatly on the setup of your scene file. Be sure to read the description below and run a free test render to make sure that disabling this does not affect the animation in a negative way.
There are ways to hint to mental ray about animated nodes manually, in cases where the default performance might still not be optimal or the standard detection algorithm does not catch all animations.
Individual instances or whole DAG subtrees can be excluded from being considered for animation by adding a new dynamic attribute 'miAnimated' (boolean) and setting it to off. Once found on a transform node, the DAG traversal prunes the remaining subtree from animation detection (not the node itself). The Optimize Animation Detection option needs to be turned off to activate the manual overrides.
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