Hotplug of a device in a virtual machine fails with a CPU or memory admission check error

Products

• VMware vSphere ESXi

Issue/Introduction

Symptoms:

• You cannot hotplug a device to a virtual machine.
• Hot add of a device to a virtual machine fails with a CPU or memory admission check error.
• You see one of these errors:
  • cannot admit VM: Memory admission check failed.
  • Can't admit VM: CPU admission check failed.

Environment

VMware vSphere ESXi

Cause

Hotplug operation involves Fast Suspend & Resume (FSR) of the virtual machine. A shadow copy of the virtual machine is created for a very brief period of time during FSR. This shadow virtual machine requires the same memory and CPU resources as the original virtual machine. If the original virtual machine has CPU and/or memory reservations, the same reservations apply to the shadow virtual machine also. If the ESXi host does not have sufficient resources to accommodate the shadow virtual machine, the hotplug operation fails with CPU and/or memory admission check errors.

Resolution

To resolve this issue, use one of these options:

• Ensure that there are sufficient free CPU and memory resources available on the host by increasing the resource allocation for the resource pool. For more information, see the vSphere Resource Management.
  
  Alternatively, free up some of the resources by moving some virtual machines to different hosts.
  
  
• Move the virtual machine to a host with sufficient available resources and then retry the hotplug operation.
• Add the devices when the virtual machine is in a powered off state. When the virtual machine is powered off, there is no FSR and, therefore, additional CPU/memory resources are not required.

Additional Information