Virtual Machine Troubleshooting Scenario – Content ID Mismatch

One of the most frustrating issues that comes up with VMs can be snapshots. In fact, our first few virtual machine troubleshooting scenarios will be focused on snapshots. Occasionally you will receive errors that return a content ID mismatch error like the one below.

Cannot open the disk ‘/vmfs/volumes/4a496b4g-eceda1-19-542b-000cfc0097g5/virtualmachine/virtualmachine-000002.vmdk’ or one of the snapshot disks it depends on. Reason: The parent virtual disk has been modified since the child was created.

Content ID mismatch conditions are triggered by interruptions to major virtual machine migrations such as Storage vMotion or Migration, VMware software error, or user action.

The Content ID (CID) value of a virtual machine disk descriptor file aids in the goal of ensuring content in a parent virtual disk file, such as a flat or base disk, is retained in a consistent state. The child delta disks that derive from that base disk’s snapshot contain all further writes and changes. These changes depend on the source disk to remain intact.

To resolve, open the latest vmware.log and locate the specific disk chain affected. You will see a line or warning that is similar to Content ID mismatch (parentCID ed06b3ce != 0cb205b1)

In our case change the parentCID in the disk descriptor file from ed06b3ce to 0cb205b1. Then overwrite the existing vmdk file and power the machine back on.

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