ESXi consolidate space on thin disk

How to reclaim disk space on thin provisioned disk

ESXi thin disk format uses a sparse file format to allow OS layer partitions to appear larger than the physical  virtual hard disk file.  OS layer data deleted from the virtual hard disk file is removed from the virtual file allocation table however the contents of the file remain allocated in the virtual hard disk file, preventing the space being reclaimed by ESXi.  Before the space can be reclaimed the remaining data must be set to zeros.

1. On Windows platforms the sdelete (secure delete) utility from the sys internals tool set can be used to zero deleted data.  The sdelete utility should be executed using an elevated console prompt on the affected VMWare guest.

https://docs.microsoft.com/en-us/sysinternals/downloads/sdelete
https://download.sysinternals.com/files/SDelete.zip

syntax:
sdelete64 -z [target disk]
e.g. sdelete64 -z c:

2. To reclaim the space, shut down the VMware guest and use vmkfstools to recover the space.  vmkfstools can be executed from an ssh console on the ESXi hypervisor
syntax: vmkfstools -K [target virtual disk].vmdk
e.g vmkfstools -K /vmfs/datastore1/myvm/myvmvmdk

DO NOT attempt to run vmkfstools against the -flat.vmdk file.