As it is running Server Core, then we need to use Computer Management snap-in from another server.
Here is some trick to make sure you able to access "Disk Management" without encounter an error.
a) Use another server running Windows Server 2008 R2 - with GUI. Don't use higher version of operating system.
b) Execute the following command at
1. Hyper-V Host (Server Core)
netsh advfirewall firewall set rule group="Remote Volume Management" new enable=yes
Netsh advfirewall firewall set rule group=”Windows Firewall Remote Management” new enable =yes
Netsh advfirewall firewall set rule group=”remote administration” new enable=yes
2. On the machine running GUI, execute
Netsh advfirewall firewall set rule group=”Remote Volume Management” new enable=yes