Storing and retrieving user data files includes, in a file storing operation, applying a first mapping (e.g. hash function) to a file identifier to originate a content address in a flat content address space; applying a second mapping (e.g., grouping of digits/characters) to the content address to originate a multi-level directory name usable in a file system; invoking the file system to store the user data file in the named directory. A file retrieving operation includes applying the first mapping to the file identifier to regenerate the content address; applying the second mapping to the regenerated content address to regenerate the directory name; invoking the file system using the regenerated directory name to retrieve the user data file. The method enables a general-purpose network attached storage (NAS) system to store files organized according to a legacy content-addressed storage (CAS) model of existing applications.