RAM display issue for Windows Server virtual machines

Problem

For a virtual machine (VM) running Windows Server as the guest operating system (OS):

• the platform's web interface incorrectly displays the used RAM value;
• the system generates low-memory warnings and sends corresponding email notifications, while actual memory usage inside the VM remains low.

This issue occurs because the guest OS lacks the balloon service, which is required for correct dynamic memory management in KVM. For Windows Server, this service is not installed automatically alongside the main virtio drivers and QEMU Guest Agent.

Diagnosis

To confirm the cause of the issue:

1. Check the guest OS version:
   
   1. Navigate to Virtual Machines → select the VM → OS field.
   2. Ensure the OS is listed as Windows Server.
2. Compare RAM metrics:
   
   1. Check real RAM usage inside the VM:
      
      1. On the target VM, open Task Manager → Performance tab → Physical Memory section.
      2. Note the value.
   2. Check the RAM value in VMmanager:
      1. Navigate to Virtual Machines → select the VM → Parameters → Information → RAM tab.
      2. Compare the values. Expected result: The values differ significantly.
3. Check for the balloon service in the guest OS:
   
   1. On the target VM, open Task Manager → Services tab.
   2. Ensure the balloon service is absent or not running.

Solution

To resolve the issue, manually install the balloon service in the guest OS:

1. Download the virtio-win-0.1.137.iso image.
2. Mount the downloaded image to the guest OS.
3. From the mounted image, install QEMU Guest Agent and the virtio drivers.
   
   Important

   For compatibility, all virtio-win components and guest additions must be installed from the same virtio-win image.
4. Copy the Balloon/2k8R2/amd64 directory from the mounted virtio-win image to the VM, for example, to C:\virtio\Balloon.
5. Launch Command Prompt as Administrator.
6. Navigate to the balloon service directory in the command prompt and install the service:
   

   cd C:\virtio\Balloon\amd64
   .\blnsvr.exe -i

7. Restart the VM. In the VMmanager web interface, go to Virtual Machines → select the VM → menu → Restart.
8. Verify that the RAM metrics for the VM in the platform now match the real values.