The present invention provides a method for keeping a file system in a consistent state and for creating read-only copies of a file system. Changes to the file system are tightly controlled. The file system progresses from one self-consistent state to another self-consistent state. The set of self-consistent...http://www.google.com/patents/US6721764?utm_source=gb-gplus-sharePatent US6721764 - Copy on write file system consistency and block usage
