Backup Proxy VM power-on fails with locked or missing virtual disk errors

Products

VMware vSphere ESXi

Issue/Introduction

Powering on a backup proxy virtual machine from the vSphere Client fails with error messages similar to the following:
Unable to access file since it is locked
The system cannot find the file specified
Review of the /vmfs/volumes/<datastore_name>/<backup_proxy_vm_name>/vmware.log for the Backup-Proxy virtual machine reveals entries associated with disks owned by other virtual machines that are currently mounted by this proxy VM:

YYYY-MM-DDThh:mm:ss In(05)+ vmx - Power on failure messages: VMware ESX cannot find the virtual disk "/vmfs/volumes/<datastore_name>/<other_vm_name_1>/<other_vm_name_1>-00000#.vmdk". Verify the path is valid and try again.
YYYY-MM-DDThh:mm:ss In(05)+ vmx - The system cannot find the file specified
YYYY-MM-DDThh:mm:ss In(05)+ vmx - Cannot open the disk '/vmfs/volumes/<datastore_name>/<other_vm_name_1>/<other_vm_name_1>-00000#.vmdk' or one of the snapshot disks it depends on.
YYYY-MM-DDThh:mm:ss In(05)+ vmx - Module 'Disk' power on failed.
YYYY-MM-DDThh:mm:ss In(05)+ vmx - VMware ESX cannot find the virtual disk "/vmfs/volumes/<datastore_name>/<other_vm_name_2>/<other_vm_name_2>-00000#.vmdk". Verify the path is valid and try again.
YYYY-MM-DDThh:mm:ss In(05)+ vmx - The system cannot find the file specified
...
YYYY-MM-DDThh:mm:ss In(05)+ vmx - Cannot open the disk '/vmfs/volumes/<datastore_name>/<other_vm_name_3>/<other_vm_name_3>-00000#.vmdk' or one of the snapshot disks it depends on.
YYYY-MM-DDThh:mm:ss In(05)+ vmx - Locking conflict for file "/vmfs/volumes/<datastore_name>/<other_vm_name_3>/<other_vm_name_3>-00000#-sesparse.vmdk". VMFS on-disk lock owner is host with MAC address <####-####-####-####> and VMFS lock mode 0x1.
YYYY-MM-DDThh:mm:ss In(05)+ vmx - Locking conflict for file "/vmfs/volumes/<datastore_name>/<other_vm_name_3>/<other_vm_name_3>-00000#-sesparse.vmdk". Kernel open flags are 0x8. Owner process on this host is world ID ######## with world name vmx-vcpu-0:<vm_name_3>.
YYYY-MM-DDThh:mm:ss In(05)+ vmx - Failed to lock the file
YYYY-MM-DDThh:mm:ss In(05)+ vmx - Cannot open the disk '/vmfs/volumes/<datastore_name>/<other_vm_name_3>/<other_vm_name_3>-00000#.vmdk' or one of the snapshot disks it depends on.
YYYY-MM-DDThh:mm:ss In(05)+ vmx - Failed to start the virtual machine.
Upon reviewing the Edit Settings>Hard disks of the Backup-proxy virtual machine, it is found to be locking one or more of the other virtual machine's vmdk files in the environment.

Environment

VMware vSphere ESXi 7.x
VMware vSphere ESXi 8.x
VMware vSphere ESXi 9.x

Cause

The Backup-Proxy virtual machine is incorrectly mounting VMDK files that are owned by other virtual machines. As a result during power-on, the ESXi Host where it resides encounters a Locking conflict for file error if the target VMDK is actively mounted and locked by another powered-on virtual machine. Alternatively, a The system cannot find the file specified error occurs if the erroneously mounted VMDK has been subsequently deleted or moved from its original directory path.

Resolution

If the Backup-Proxy VM is in an inaccessible state, unregister the virtual machine from the vSphere inventory and register it again. Then, unmount the foreign VMDKs by proceeding with the following steps:

Right-click on the Backup-Proxy virtual machine and select Edit Settings.
Verify the required OS and Data drives strictly native to the Backup-Proxy VM configuration.
Review the remaining attached hard disks to identify VMDK files belonging to other virtual machines.
On the right side of each foreign hard drive entry, click on the X icon to detach the disk.
Verify that the Delete files from datastore checkbox is explicitly unchecked to prevent data loss.
Repeat the detachment process for any additional VMDK files not strictly owned by the Backup-Proxy VM.
Click OK to save the hardware configuration changes.
Power on the Backup-Proxy virtual machine.

Additional Information

Deleting a vmdk file for a virtual machine that is no longer used fails: Device or resource busy

Investigating Virtual Machine file locks on ESXi Host(s)