File cloning and de-cloning in a data storage system

A file cloning mechanism allows for quickly creating copies (clones) of files within a filesystem, such as when a user makes a copy of a file. In exemplary embodiments, a clone of a source object is at least initially represented by a structure containing references to various elements of the source object (e.g., indirect onodes, direct onodes, and data blocks). Both read-only and mutable clones can be created. The source file and the clone initially share such elements and continue to share unmodified elements as changes are made to the source file or mutable clone. None of the user data blocks or the metadata blocks describing the data stream (i.e., the indirect/direct onodes) associated with the source file need to be copied at the time the clone is created. At appropriate times, cloned files may be "de-cloned."