Virtual Machine Snapshot Disk Consolidation Fails With Error "The parent virtual disk has been modified since the child was created"

Products

• VMware vCenter Server

Issue/Introduction

• Snapshot consolidation fails on a VMware virtual machine (VM), and the system reports an error indicating a content ID mismatch between the parent and child virtual disks. This commonly occurs when one or more essential snapshot disks (.vmdk files) are missing from the VM's directory, thereby breaking the snapshot chain.

• An error task similar to  the following could be seen while trying to create or delete or consolidate snapshots on the VM:  

An error occurred while consolidating disks: The parent virtual disk has been modified since the child was created. The content ID of the parent virtual disk does not match the corresponding parent content ID in the child.

Environment

VMware vSphere 7.x

VMware vSphere 8.x

Cause

The root cause is a broken snapshot chain, which prevents the consolidation process. This issue is triggered by:

• Missing Snapshot Disks: One or more delta disk files (e.g., `VMNAME-00000X.vmdk` and its corresponding `VMNAME-00000X-delta.vmdk`) are missing from the VM's directory.

• Content ID Mismatch: The absence of the disk files modifies the parent-child relationship in the snapshot chain. When consolidation is attempted, the Content ID (CID) of the parent virtual disk no longer matches the Parent Content ID (PID) recorded in the child disk's metadata, leading to the "parent virtual disk has been modified" error.
  
  

When snapshot disks are permanently missing from the datastore, the snapshot chain cannot be repaired, and consolidation or cloning operations are not possible.

Example Showcasing the Missing Disks:

The disk files in a virtual machine's snapshot chain are typically numbered sequentially (e.g., -000001, -000002, -000003, etc.).

In the list of files provided:

File Sequence	Files Present
-000001	VM-NAME-000001-delta.vmdk, VM-NAME-000001.vmdk
-000002	VM-NAME-000002-delta.vmdk, VM-NAME-000002.vmdk
-000003	VM-NAME-000003-delta.vmdk, VM-NAME-DMDB01-000003.vmdk
-000004	(Missing)
-000005	VM-NAME-000005-delta.vmdk, VM-NAME-000005.vmdk

The absence of `VM-NAME-000004-delta.vmdk` and `VM-NAME-000004.vmdk` is evident because the file names jump directly from ...-000003... to ...-000005.... This break in the numerical sequence is what causes the Content ID mismatch errors and prevents snapshot consolidation, as the disk with suffix -000005 expects its parent to be -000004.

Please see, "The parent virtual disk has been modified since the child was created" error for more details. 

Resolution

The virtual machine must be restored from a recent backup to ensure a consistent operating state.