Thinprovisioning will be a new feature of the next release of ESX. However, it is already possible to use thinprovisioning from the service console with the vmkfstools command. Here are some tips (thanks to Richard Garsthagen):

Create a 15GB thinprovisioned disk:

vmkfstools -c 15G -d thin /vmfs/volumes/vmfs_volume/VM_name/thin_disk.vmdk

If you want to convert a thick disk, you can create a copy from it as thin disk. After that, you will need to remove the old disk from the VM and add the new converted copy. … Continue Reading