Taking a snapshot or cloning the virtual machine fails with the No child processes error

Products

• VMware vSphere ESXi

Issue/Introduction

Symptoms:

• Cannot take a snapshot or clone the virtual machine
• Taking a snapshot or cloning the virtual machine fails
• You see the error:
  
  No child processes
  
  
• The Windows Task and Events log reports the error:
  
  Cannot open the disk /vmfs/volumes/Datastore/VM/VM-000003.vmdk or one of the snapshot disks it depends on. Reason: No child processes.
  
  
• In the vmkernel.log file, you see entries similar to:
  
  vmkernel: 501:23:33:35.536 cpu0:156722052)Sched: vm 156722054: 1043: name='vmm1:VM'
  vmkernel: 502:00:00:36.837 cpu2:156711206)WARNING: Cow: 1436: Opening the cow hierarchy VM-000003-delta.vmdk failed with I/O error
  
  
• In the vmware.log file, you see entries similar to:
  
  vmx| DISK: Cannot open disk /vmfs/volumes/4a2ee544-74e51ff8-5630-0019bccb08e8/vm1/vm1-000003.vmdk: No child processes (655369).
  Msg_Post: Error
  
  [msg.disk.noBackEnd] Cannot open the disk /vmfs/volumes/Datastore/vm1/vm1-000003.vmdk or one of the snapshot disks it depends on.
  
  [msg.disk.configureDiskError] Reason: No child processes.
  
  
• Creating a new virtual machine and attaching the disk does not resolve the issue
• Running the vmkfstools -t0 command on the disk reports the No child processes error

Environment

VMware vSphere ESXi 5.0
VMware vSphere ESXi 5.1
VMware vSphere ESXi 5.5

Cause

This issue occurs if the.vmdk delta file or snapshot disk is corrupted.

Resolution

To resolve this issue, restore the virtual machine from a back up.

Additional Information

For more information, see the VMware Communities article Cannot open disk "/vmfs/volumes/xxx.vmdk": No child processes (655369).

Best practices for using snapshots in the vSphere environment