VSAN takes advantage of capabilities surfaced by VASA, vSphere 5.5 introduced a new and simpler VAAI UNMAP/Reclaim command

VMware provides various storage related APIs in order to enhance storage functionality and integration between storage devices and vSphere.
vSphere 5.1 introduces additional VAAI NAS enhancements to enable array-based snapshots to be used for vCloud Director fast-provisioned vApps. This feature in vSphere 5.1 enables vCloud Director to off-load the creation of linked clones to the NAS storage array in a similar manner to how View does it in vSphere 5.0.
vSphere 5 had already extended the vStorage APIs by adding VASA (vSphere Storage API for Storage Awareness) and new VAAI primitives:
1) VASA : Storage Awareness is a new set of APIs that will enable VMware vCenter Server to detect the capabilities of the storage array LUNs (e.g. RAID level, SATA v SSD, availability) enabling to select the appropriate disk for virtual machine placement or the creation of datastore clusters. The storage hardware needs to be VASA enabled to provide this integration.
2) VAAI: vStorage API for Array Integration enables integration of array-based capabilities. It basically allows to offload task directly to storage array HW for better performance rather than executing it in software. It supports: Full copy, Block zeroing, Hardware-assisted locking
New with vSphere 5:
• vSphere® Thin Provisioning (Thin Provisioning), enabling the reclamation of unused space and monitoring of space usage for thin-provisioned LUNs (alerting if running out!)
• Hardware acceleration for NAS
• SCSI standardization by T10 compliancy for full copy, block zeroing and hardware-assisted locking
3) VAMP: vStorage API for Multi Pathing: Enables storage partners to create multipathing plugins for vendor specific capabilities.