Yesterday I by mistake extended a disk on a VM that had snapshots.
Using vmkfstools.
Kind of like this thread (http://communities.vmware.com/thread/238035).

This resulted in the following PowerOn error:

Failed to power on Servername on Host in Cluster:

Cannot open the disk ‘/vmfs/volumes/LUN/Folder/VM.vmdk’
Reason: The parent virtual machine disk has been modified since the child was created

The server was a database server so I had no choice than to fix it.

I tried the following with no luck:

  • Reverting to snapshot didn’t help – (Don’t try this if you don’t have a good backup)
  • Shrinking the vmdk again using vmkfstools – (This has not been possible since ESX 3.0)

Then I tried to use VMware Converter to do a V2V and in the first try (all defaults) that didn’t help the VM started with a BSOD.I tried again using the Converter but this time I changed one default parameter.In the “View/Edit Options” tap, remove the check mark in “Reconfigure destination virtual machine” and click YES to the warning.Removing the reconfigure option saved my day.
The VM started and I was able to restore the latest files from backup.