1. A computer-readable storage medium including instructions that upon execution by a processor cause the processor to: open a virtual disk file, the virtual disk file including a first unique identifier and virtual disk extent data that forms at least a part of the data in a virtual disk; overwrite the first unique identifier in the virtual disk file with a second unique identifier in response to detecting an attempt to write information to the virtual disk file that affects how virtual disk extent data is interpreted; determine that the second unique identifier was written to a persistent copy of the virtual disk file; and write the information to virtual disk file in response to determining that the second unique identifier was written to the persistent copy of the virtual disk file.