The VM must be powered off before the administrator can reduce its CPU allocation. CPU hot-plug capabilities permit supported guest operating systems to receive additional virtual CPU resources while running, but they do not provide a supported mechanism for removing active processors from a powered-on VM. Nutanix documentation states that the number of CPUs cannot be decreased while the VM is powered on.
After shutting down the guest cleanly and confirming that the VM is off, the administrator can edit the VM configuration, reduce the required vCPU count or associated CPU topology, save the change, and restart the VM. The proposed configuration must remain valid—for example, the relationship between sockets, vCPUs, and cores must be supported.
Enabling Hot-Add addresses CPU expansion rather than reduction. Nutanix Guest Tools supplies guest integration and operational capabilities but does not override hypervisor restrictions on CPU removal. A snapshot may be useful as an optional change-control precaution, but it does not make CPU reduction possible and is not the required first step.
The technically necessary action is therefore to power off the VM. Reference: AHV – Virtual Machine Memory and CPU Hot-Plug Configurations . NHCF alignment: modifying VM compute resources and understanding hot-plug limitations.
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