VM power-on fails with "The available Memory resources in the parent resource pool are insufficient for the operation"

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 6.x
• VMware vSphere ESXi 7.0.x
• VMware vSphere ESXi 8.0.x
• VMware vCenter Server 6.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 higher than 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

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

 

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

   1. If the memory in the ESXi host client here are different than in the vCenter Server UI

   2. Rule out a problem in the vCenter Server OS by restarting the vCenter Server and if applicable Platform Services Controller (PSC)

   3. If rebooting vCenter fails to fix the problem, there may be a communication problem between the vCenter Server and the ESXi host.
      • Troubleshoot for vCenter/ESXi host communication problems. For more information see Troubleshooting an ESXi host in a "not responding" state
      • Or make the configuration changes using the ESXi host client

2. If the settings still make no sense even from the ESXi client, the VM's information may have corrupted.
   1. 1. Unregister the VM from vCenter UI if you can, or on ESXi client level if you cannot
      2. Re-register the VM, see How to register or add a Virtual Machine (VM) to the vSphere Inventory in vCenter Server

 

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

• Remove or reduce the reservation
• 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 the 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 you should no longer see the alert in the Summary tab.

If you have performance problems with the required changes:

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

Additional Information

• Please keep in mind that changing the resource configuration of a virtual machine can impact its performance
• The issue can also 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 additional VM power on failures, please see Failed to power on virtual machine