Virtual machine fails to power on with "CID mismatch" error after attaching its snapshot VMDK to another VM

Products

• VMware vCenter Server

Issue/Introduction

• A virtual machine fails to power on.

• This issue occurs after a virtual machine disk (VMDK) file that is part of a snapshot chain is temporarily attached to a different virtual machine and powered on, and then returned to the original virtual machine.

• In the vmware.log file of the affected virtual machine, you see entries similar to the following:

YYYY-MM-DDTHH:MM:SS.mmmZ In(05)+ vmx - Power on failure messages: File system specific implementation of Ioctl[file] failed
YYYY-MM-DDTHH:MM:SS.mmmZ In(05)+ vmx - File system specific implementation of Ioctl[file] failed
YYYY-MM-DDTHH:MM:SS.mmmZ In(05)+ vmx - 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 ESXi 7.0
VMware vSphere ESXi 8.0

Cause

This issue occurs because the Content ID (CID) of a virtual disk (.vmdk) is automatically updated whenever the disk is modified or powered on.
When a VMDK file that belongs to a snapshot chain is attached to a different virtual machine and powered on, the host detects disk activity (such as an OS boot or metadata update) and assigns a new, randomly generated CID to that VMDK.
As a result, when the VMDK is returned to the original virtual machine, the snapshot chain is broken. The parentCID value recorded in the child snapshot disk no longer matches the newly updated CID of the parent disk, leading to the "Content ID mismatch" error and preventing the virtual machine from powering on.

Resolution

Warning: Do not attach a VMDK containing a snapshot to another virtual machine. This is an unsupported operation.

To attempt to repair the snapshot chain, follow the steps in KB 345254 to manually edit the CID of the modified VMDK file.
"The parent virtual disk has been modified since the child was created" error (345254)
Note: This is a best-effort procedure. It does not guarantee the successful power-on of the virtual machine or complete data recovery.

Additional Information

スナップショット VMDK を別の仮想マシンに接続した後、仮想マシンが 「CID mismatch」 エラーでパワーオンに失敗する