Virtual machine becomes temporarily unresponsive during a hot clone operation

Products

• VMware vSphere ESXi

Issue/Introduction

When performing a clone operation on a powered-on virtual machine from the vSphere Client, the virtual machine becomes temporarily unresponsive.

Environment

VMware ESXi 8.X

Cause

When cloning a powered-on virtual machine, ESXi creates a temporary snapshot to capture the state of the virtual machine. Once the cloning process is complete, this snapshot is consolidated. During the snapshot consolidation phase, the virtual machine is briefly stunned to commit the data changes from the delta disk to the base disk.

If the virtual machine is experiencing high disk I/O during the cloning process, the stun time required for snapshot consolidation increases. This extended stun time can cause the virtual machine to appear unresponsive.

- Virtual machine stun can be confirmed in the vmware.log file from entries similar to the following:

2025-01-01T01:01:01.980Z| vcpu-0| I005: Checkpoint_Unstun: vm stopped for 210187 us
2025-01-01T01:01:02.044Z| vcpu-0| I005: CPT: vm was stunned for 273536 us

Resolution

High disk I/O activity increases the stun time during snapshot consolidation. To minimize the duration of unresponsiveness, it is recommended to perform clone operations during periods of low disk I/O activity.

Additional Information

Snapshot removal stops a virtual machine for long time