Hi,
I have recently upgraded to VMFS 6. To take benefit of VMFS 6's automatic space reclamation, the VMs on those datastore needs to be thin provisioned. Once VM is thin provisioned and data is removed from inside VM, the freed space will be updated at datastore level as well.
I upgraded some datastores from VMFS 5 to 6 and thin provisioned existing thick VMs (Windows 2012) during storage migration. Once this was done, we saw increased free space at datastore level after some time.
Do note that space reclamation is a slow process by default and cannot be changed to fast.
Refer to VMware KB for configuration parameters - Configure Space Reclamation for a VMFS6 Datastore
The settings in KB are for your reference. You can go with default settings during VMFS 6 datastore creation process.
