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

    current vmdk size
    Check actual size:

    du -h *.vmdk

    actual vmdk size

  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!
    resized vmdk size

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.

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