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A virtual machine cannot boot after extending a base virtual disk that is part of a snapshot hierarchy

Details

  • A virtual machine fails to power on if you extend the base disk of a snapshot which is part of a redo hierarchy
  • You see the error:

    The parent virtual disk has been modified since the child was created

Solution

This issue may occur if the size of the base disk does not match the logical size of the redo log.
 
You must manually reset the logical size of the base disk to its original size in the disk descriptor file foo.vmdk.
 
To determine the original size of the base disk, look at the .vmdk file corresponding to the delta disk redo log. For example, an entry for a delta disk in the .vmdk file looks like:
RW 2048 VMFSSPARSE "foo-43489354-delta.vmdk"

Note: The disk size is expressed in number of sectors. In this example, the disk size is 2048, or 1MB.
The corresponding disk descriptor file foo.vmdk looks like:
# Extent description
RW 2048 VMFS "foo-flat.vmdk"
If you extend the base disk to 2MB, the foo.vmdk file looks like:
# Extent description
RW 4096 VMFS "foo-flat.vmdk"
To reset the logical size of the base disk, replace 4096 with 2048 so that the foo.vmdk file looks like:
# Extent description
RW 2048 VMFS "foo-flat.vmdk"

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Actions
  • KB Article: 1646892
  • Updated: Aug 14, 2009
  • Products:
    VMware ESX
  • Product Versions:
    VMware ESX 3.0.x