"The available Memory resources in the parent resource pool are insufficient for the operation" when trying to power-=

Products

• VMware vCenter Server
• VMware vSphere ESXi

Issue/Introduction

• When trying to power on a virtual machine (VM) in vSphere Client, the task fails with an error message:

  The available Memory resources in the parent resource pool are insufficient for the operation

• When using the ESXi host client instead, the power on operation fails with a similar error.

Environment

• VMware vSphere ESXi 7.0.x
• VMware vSphere ESXi 8.0.x
• VMware vCenter Server 7.0.x
• VMware vCenter Server 8.0.x

Cause

Some potential causes for the issue can include:

• VM memory reservation settings are higher than the the amount the ESXi host can support
• VM configuration information is corrupted in the ESXi/vCenter database
• ESXi OS problem
• vCenter Server OS problem
• vCenter/ESXi host communication problem
• ESXi host server hardware configuration problem

Resolution

1. Verify the virtual machine and ESXi host memory resources:

   1. Check the memory reservation settings for the VM. Reserved resources are not subject to ESXi scheduling / memory reclamation and must be available in the physical memory of the host
   2. Confirm that the ESXi the VM is registered on has enough free memory to accommodate the VM.
   3. Check if the virtual machines is part of a resource pool and confirm that the resource pool has enough free memory
   
   
   

2. If there are no memory constraints seen:

   1. Connect directly to the ESXi host client for the host managing the VM and recheck the settings:
      • Check if ESXi Host Client displays different memory settings for the VM than vSphere Client.
      • If so, restart the vCenter Server to rule out any OS-side issues.
      • If rebooting vCenter fails to fix the problem, there may be a communication issue between the vCenter Server and the ESXi host.
        1. Troubleshoot for vCenter/ESXi host communication problems. For more information see Troubleshooting an ESXi host in a "not responding" state
        2. Or change the VM memory configuration changes using the ESXi host client
      • If the ESXi host client displays invalid settings or fails to display the VM settings, the VM configuration might be corrupt.
        • Unregister the virtual machine using either vSphere Client or ESXi host client
        • Re-register the VM, see How to register or add a Virtual Machine (VM) to the vSphere Inventory in vCenter Server
   
   
   

3. If the numbers indicate there is a problem with the memory reservation:

   1. Remove or reduce the memory reservation
   2. Alternatively, increase the ESXi host's resources or move the VM to another host with adequate resources

   To remove or reduce the reservation:

   1. Locate the affected VM
   2. In vSphere Client, right-click the virtual machine and click Edit Settings..
   3. Under Virtual Hardware expand Memory and CPU
   4. Reduce the reserved CPU/memory value or set it to 0 to remove the reservation.
   5. Click OK. The virtual machine reconfigures and the alert in the Summary tab should disappear.

If there are performance problems after implementing the required changes:

1. Add more resources to the hosts to allow you to increase the memory resource as before.
2. Or, consult with the application or guest OS vendor.

Additional Information

• Keep in mind that changing the resource configuration of a virtual machine can impact its performance.
• Similar issues can occur if the Latency Sensitivity of a virtual machine is set to HIGH, as this requires the complete VM memory (and CPU) to be reserved. Refer to Configure the Virtual Machine Latency Sensitivity for more information.
• For additional VM power on failures, see also Failed to power ON virtual machine.