The subject matter of this specification can be implemented in, among other things, a method that includes receiving, from within a guest operating system, a request to create a data file in a guest file system of the guest operating system. The method further includes in response to the receipt of the request to create the data file, creating an external data file in a first storage device for a file system outside the guest file system, creating a sparse file in the guest file system, and storing metadata that directs requests to access the sparse file from within the guest operating system to the external data file in the first storage device.