One aspect involves mounting a file system stored on a CAS system. The file system has a directory structure that includes a plurality of directories arranged in a hierarchy and including a root directory at the top of the hierarchy. Each of the directories is represented by a content unit stored on the CAS system, the content unit having a content address that is computed based, at least in part, on at least a portion of the content of the content unit. The file system is mounted by specifying the content address of the content unit that represents the root directory and determining the file system to be mounted based on the content address of the content unit that represents the root directory.