We received a warning message from the 2012 R2 system which I installed a long time ago with VM storage type: Thin. So, it cannot modify HDD size although it is a VM system. We looked for a way to increase HDD space without losing any data or delete any files.
Well, here is the easiest way to resolve the issue.
Step1, Create a clone of the Windows 2012R2 system without power down.
Step2, Choose “Thick Provision Lazy Zeroed” from Select virtual disk format
Step3, Power down original Windows 2012R2 system.
Step4, Power on the clone Windows 2012R2 system.
Step5, Extend disk volume (C:) from server manager / Files and Storage Services / Volumes / Disk. (no power down required)
Step6, Verify all the functions are working properly.
Notes, making sure the time clock is matched with your DC servers.