VM Hot Add CPU Or Memory

Private Cloud Director supports hot-add of CPU and / or memory resources to a running virtual machine. Using this feature, you can increase CPU cores or memory allocated to a running VM, without having to power-cycle it. This is valuable for production VMs that need more resources to meet workload demands but that can not be powered off.

Pre-requisites

• Read more here about Zero-Size Flavor. Using zero-size flavor when creating your VM is a requirement for hot-add. Before you can hot-add CPU or memory resources to a VM, the VM must have been created using zero-size flavor.

Hot-add CPU or Memory to a Running VM

1. Select a powered-on VM that was created with a zero-size flavor.
2. On the VM grid view, navigate to ▷ Other Actions ▷ Hotplug.
3. Enter the new vCPU and/or memory value for the VM. The maximum values you can enter are set by the VM's flavor, using the Hotplug vCPUs Maximum and Hotplug RAM Maximum values configured on that flavor.
4. Click Hotplug VM.

Limitations

• Hot add can only be used to increase the current CPU or memory allocation of a running VM. Reducing currently allocated CPU or memory is supported only while the VM is stopped.
• You can not use the hot-add feature to resize the disk of a running VM today.
• On VMs running Windows Server 2022, the guest OS's System Information (systeminfo) may display the flavor's maximum configured hotplug memory value instead of the VM's current memory allocation after a memory hot-add operation.
• Hot-add-capable VMs that boot from a persistent volume and were created before the PCD 2025.10 release may fail to live migrate until a one-time corrective hotplug is applied. See Resolve Live Migration Failures for Legacy Boot-from-Volume Hotplug VMs.