Hi Ronald,
You need to have the FULL space available that your virtual disk can use.
What sdelete does is write out zero's and while it is doing that it will inflate the virtual disk.
Beware that you have to use the correct syntax (it changed somewhere over the years, according to my notes you have to use the -z option for zeroing out as of version 1.6)
So the effect of sdelete is that your virtual disk wlll take up the full space that was reserved for use.
Eg. if your thin virtual disk is 1.5TB in size, it will take up 1.5TB when your sdelete is done with zeroing out the empty space.
The reclaiming happens when you run the vmkfstools --punchzero (or -K) option. The main disadvantage of that method is that you can only do that after shutting down the VM.
The alternatives discussed earlier on in the thread do not need downtime, but do need appropriately sized LUNs with enough free disk space to perform the storage vmotion.
--
Wil