We got a request to reduce the allocated size of Thick provisioned Virtual machines hard disk. Increasing the VMDK size can be done in GUI but decreasing the size of VMDK is not allowed. In most cases, For virtual machine hard disk shrink can be performed via v2v. It is the safest method to reduce the virtual machine VMDK size but there is an another simple approach which saves lot of efforts rather than performing v2v. The below approach is tested in Windows 2008 Operating systems but it may corrupt your data so i would strongly suggest prepare a back out plan before perform the disk shrink. One more note to perform the disk shrink is perform a shrink operation from the OS side using shrink feature in windows 2008 and then follow the below procedure.

1. Navigate to Virtual Machine path from your ESX SSH session

            cd /vmfs/volumes/Datastore_name/VM_Name

2. Edit the VM_Name.vmdk file using Nano or vi editor,

      Below is the content of  .vmdk file.

Let us understand what it is and how do we understand disk size. In the above screenshot, Size of the disk shows 83886080. How it is calculated. It is nothing but 40 GB.

40 GB = 40*1024*1024*1024/512  =  83886080

The below GUI snap confirms that VM has 40 GB assigned vmdk..

Lets say for 50 GB = 50*1024*1024*1024/512 = 104857600

To shrink the disk , Edit the descriptor file by vi VM_Name.vmdk ie. vi test.vmdk

Under extent description replace value between RW _ _ _ _ _ VMFS *-flat.vmdk. In my case it was 40GB disk assigned and hence the value was 83886080. I want to reduce the vmdk by 10 GB so after the shrink vmdk size should be 30GB.

So for 30 GB, use the below mentioned calculation

30(1024*1024*1024)/512 = 62914560  and save the file. svmotion the vm to forth and back then VM properties now reflect the new size of the disk 30 GB

I hope the above steps are helpful for you. Thanks for reading !!!