1. A method comprising: receiving a first request to create or extend a file; allocating a set of allocation units for the file on a primary storage medium without initializing the set of allocation units on the primary storage medium; associating the set of allocation units with file template metadata comprising at least one pattern; receiving a second request to access a particular allocation unit, of the set of allocation units; responsive to the second request, generating at least a portion of the particular allocation unit based on the at least one pattern; wherein the method is performed by one or more computing devices.