Q: Will Windows Server 2012 let you shrink and expand virtual hard disks (VHDs) while online?

A: Windows Server 2012 introduces the ability to merge snapshots for virtual hard disks (VHDs) while they are online, in addition to the ability to set the parent VHD and mirror operations. However, the ability to shrink, expand, compact and convert a VHD isn't possible while the VHD is online. Any virtual machine (VM) using the VHD will need to be stopped before you attempt these operations.