VAAI UNMAP was introduced in vSphere 5.0 to reclaim the free space when the VMs had to be moved or deleted from a datastore that is thin provisioned at the storage level. vSphere 6.0 introduced some improvements to UNMAP that facilitated the reclaiming of stranded space from within a guest OS.
But, in this case, the reclaim operation was performed manually, as described on KB 2057513—Using the esxcli storage vmfs unmap command to reclaim VMFS deleted blocks on thin-provisioned LUNs at https://kb.vmware.com/kb/2057513.
In vSphere 6.5 and with the new VMFS6, there is now an automated UNMAP mechanism for reclaiming the dead or stranded space on datastores. Now UNMAP runs continuously in the background if enabled at the ...
