One of the biggest changes introducted In vSphere 6.5, was the ability to run an automated UNMAP at the datastore level and inside the guest os (for both windows and linux VMs that support the SCSI primitive)
Unfortunately, the GA release of vSphere 6.5, had a bug in it that prevented the in-guest UNMAP from running properly, I wrote about it here
we’ve been working with VMware on resolving this issue (it’s not a storage array specific issue) so everyone will benefit from the fix and today (15/03/2017), the fix has been released!
“Tools in guest operating system might send unmap requests that are not aligned to the VMFS unmap granularity. Such requests are not passed to the storage array for space reclamation. In result, you might not be able to free space on the storage array.”
So there you go, if you are looking for THE most compelling reason to upgrade to vSphere 6.5, this is it!