Which feature in vSphere 6.5 allows the backing storage…

In vSphere 6.5, a virtual machine is thinly-provisioned on a VMFS6 datastore. The administrator deleted a large
file within the guest OS. The freed blocks in the datastore are no longer needed by the VM.
Which feature in vSphere 6.5 allows the backing storage to automatically reclaim the freed blocks?

A.
ATS

B.
Defrag

C.
UNMAP

D.
Auto Reclaim

Explanation:
VAAI UNMAP was introduced in vSphere 5.0 to allow the ESXi host to inform the backing storage that files or
VMs had be moved or deleted from a Thin Provisioned VMFS datastore. This allowed the backing storage to
reclaim the freed blocks. There was no way of doing this previously, resulting in many customers with a
considerable amount of stranded space on their Thin Provisioned VMFS datastores.