Your storage don't know about the data that you removed from the VMFS, because of this you may need tools like vmkfstools/esxcli to inform your storage arrays about the deleted files and allow your array reclaim the freed blocks.
Take look at the following links:
http://blogs.vmware.com/vsphere/2012/04/vaai-thin-provisioning-block-reclaimunmap-in-action.html