One of the basic operations that V-Ray must perform is raycasting – determining if a given ray intersects any geometry in the scene, and if so - identifying that geometry. The System rollout also includes parameters that control V-Ray's Binary Space Partitioning (BSP) tree. However, dividing the frame between too many buckets can slow down the rendering because there is some time overhead related with each bucket (bucket setup, LAN transfer, etc). Because a bucket can be processed only by a single processor, the division of the frame in too small number of buckets can prevent the optimal utilization of computational resources (some CPUs stay idle all the time).

Buckets can be sent to idle LAN machines for processing and/or can be distributed between several CPUs. A bucket is a rectangular part of the currently rendered frame that is rendered independently from other buckets. The bucket is an essential part of the distributed rendering system of V-Ray. The System rollout gives you access to various parameters including those that control V-Ray's rendering regions (buckets).

Vray 5 for 3d max