Virtual machine hangs or restarts during incremental snapshot consolidation

Products

• VMware vSphere ESXi

Issue/Introduction

When executing incremental snapshot tasks (creation, deletion, or consolidation), the following symptoms occur:

• The virtual machine (VM) hangs and unexpectedly powers off or restarts.
• vCenter Server may show snapshot tasks as "Completed," but the VM becomes unstable immediately after.
• The following errors appear in ESXi host at following location /var/vmfs/<Datastore_UUID>/<Virtual_Machine_Directory>/vmware.log: 
  ####-##-##T##:##:## In(05) vcpu-0 [msg.poweroff.commitOn] Performing disk cleanup. Cannot power off. ####-##-##T##:##:## In(05) vcpu-0 [msg.disklib.lockinfo.local] Locking   conflict for file "/vmfs/volumes/########/####/####.vmdk"
• Following error is observed in /var/run/log/hostd.log on ESXi host:
  An operation required the virtual machine to quiesce and the virtual machine was unable to continue running.

Environment

VMware ESXi 8.x

VMware vCenter Server 8.x

Cause

This issue is caused by resource contention and file lock conflicts resulting from the simultaneous execution of a third-party backup job and a separate incremental snapshot/consolidation task on the same virtual machine.

When both operations attempt to manipulate the VMDK file chain at the same time:

1. The backup software opens a session via NFC to read the snapshot disk (00000#.vmdk).

2. Simultaneously, vSphere attempts to complete a snapshot consolidation, which requires merging delta disks and unstunning the VM.

3. Because the backup process is still interacting with the file chain, ESXi encounters a Locking conflict.

4. To prevent severe disk corruption or data inconsistency, the ESXi hypervisor intentionally terminates (powers off) the VCPU threads.

Resolution

1. Stagger Schedules: Ensure that internal incremental snapshot testing schedules do not overlap with production backup windows.
2. Pause Backups During Testing: Temporarily disable or pause automated backup policies for the specific VM while performing manual snapshot or disk consolidation maintenance.
3. Review Backup Vendor Configuration: If both tasks are initiated by the same automation or backup suite, contact your software vendor (e.g., Nutanix Support) to optimize the snapshot integration and serialization settings.