Converting thick provisioned disks to thin provisioned not reducing space used

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http://serverfault.com – I have followed these steps to convert a .vmdk virtual disk from thick-provisioned to thin-provisioned, however, a 50GB disk with 30GB free is still taking up 50GB. vSphere is showing the disks as thin-provisioned. Any ideas? Update: This is on an ESXi 5 hypervisor, Single SAN storage (HowTos)