Shrink a thin provisioned VMDK disk

When maintaining a Horizon View environment I like to keep my parent images as small as possible and over time a thin provision disk can start to grow on you if you don’t watch it – be it from downloading installers, updates, or even running disk defrag. While there isn’t a simple, one click button in the View Administrator Console there is a fairly easy manual method using vmfkstools.

Before we can use “vmkfstools” to shrink the VMDK file we must zero out any unused space on the thin provisioned disk. A simple way of doing this is by using a free utility called SDelete from Sysinternals.

1. Download SDelete onto the VM you want to shrink and run the following command, replacing [DRIVE:] with the actual drive letter to be reduced:

   sdelete.exe -z [DRIVE:]

   Note: In Linux VM’s you’ll want to run this command, replacing [PATH] with the actual path of the storage:

   dd if=/dev/zero of=/[PATH]/zeroes bs=4096 && rm -f /[PATH]/zeroes

2. Power off the VM and SSH into your ESXi host and navigate to the VMDK’s datastore -> directory and check the VM’s current size by typing:
   Check virtual disk size:

   ls -lh *.vmdk

   
   Check actual size:

   du -h *.vmdk

   

3. Now we’ll punch all the zeroed blocks out of the VMDK file by typing, replacing [DISK] with the name of the VM VMDK file:

   vmkfstools --punchzero [DISK].vmdk

4. Once complete, again check the size by repeating step 2. If all went well you should now have a smaller VMDK file and newly reclaimed space!
   

If you do this on the parent image of a View Pool the changes won’t be “pushed” out to the VM’s within the Pool until your next recompose.