Logon to the ESXI Server where the VM is stored using a product like putty.
Ensure the VM is turned off.
The following command lists the datastores:
“ls” is used to List subregions – used to list out files in a directory.
ls /vmfs/volumes
ls /vmfs/volumes/ESX01_Internal1/
ls /vmfs/volumes/ESX01_Internal1/RDS2012/
"vmkfstools -k /vmfs/volumes/ESX01_Internal1/RDS2012/RDS2012.vmdk"
Use “vmkfstools -k” to convert a Lazy Zeroed disk to a Eagerly Zeroed disk.
Ryan Mangan's IT Blog 
Does the VM have to be powered off for this to work? I tried this with a running vm and got a lock error.
Hi, yes you would need to shutdown the VM to convert a VMDK.
Good Article with snapshots, very informative.
Hi, thx for this good instruction. Process is done and looking fine. But the disk with in the VM properties is still shown as lazy-zeroed!? Is this correct?
You will need to remove the disk from the virtual machine and then reattach.
Hi Christian,
You can check the type of VMDK by using the command “vmkfstools -D”
If the output appears similar to the following with tbz at zero, the VMDK is eagerzeroedthick. Otherwise it is zeroedthick.
I find that by starting the VM, it will re-register the VM and update the properties. You should see that the VM properties will show eager or Lazy. You can also reattach the disk to the VM as Reed mentioned.
Best Regards,
Thank you!
It showed the disk to be a lazy zeroed one. After reattaching the disk to the vm it now shows the correct format.
Best regards,
Thank you for the great article. For the benefit of anyone else viewing this article, there are a few errors. The instructions incorrectly state (last two lines):
ls vmfstools -k /vmfs/volumes/ESX01_Internal1/RDS2012/RDS2012.vmdk
Use “vmfstools -k” to convert a Lazy Zeroed disk to a Eagerly Zeroed disk.
Using the command listed here results in receiving the error “ls: vmfstools: No such file or directory”. As is correctly used in the screenshot, you should omit the “ls” and the command is “vmkfstools” and not “vmfstools”.
Dear Reed, Thank you for highlighting the Typos. This has now been altered to show “vmkfstools” as per my screenshot.
“ls” is used to list out files in the directory (List subregions), readers may use this when locating the VMDK they want to convert but its not used when running the conversion command.
Best Regards,