Explanation/Reference:
Ref: http://technet.microsoft.com/en-us/library/dn282286.aspx
Requirements
The following functionality is required for resizing a virtual hard disk:
* A server capable of running Hyper-V. The server must have processor support for hardware virtualization. The Hyper-V role must be installed.
* A user account that is a member of the local Hyper-V Administrators group or the Administrators group.
The following functionality is required for resizing a virtual hard disk:
* VHDX - the ability to expand and shrink virtual hard disks is exclusive to virtual hard disks that are using the .vhdx file format. Online resizing is supported for VHDX disk types, including fixed, differencing, and dynamic disks. Virtual hard disks that use the .vhd file format are not supported for resizing operations.
* SCSI controller - the ability to expand or shrink the capacity of a virtual hard disk is exclusive to .vhdx files that are attached to a SCSI controller. VHDX files that are attached to an IDE controller are not supported.