With ESXi, you can use two models of thin provisioning, array‐level and virtual disk‐level.
Thin provisioning is a method that optimizes storage utilization by allocating storage space in a flexible on-demand manner. Thin provisioning contrasts with the traditional model, called thick provisioning. With thick provisioning, large amount of storage space is provided in advance in anticipation of future storage needs. However, the space might remain unused causing underutilization of storage capacity.
The VMware thin provisioning features help you eliminate storage underutilization problems at the datastore and storage array level.