A read-write snapshot copy facility is constructed from a hierarchical storage management facility. The read-write snapshot copy file system initially comprises stub files pointing to the files in a read-only snapshot copy file system. When an application writes to a file in the read-write snapshot copy,...http://www.google.com.au/patents/US7546431?utm_source=gb-gplus-sharePatent US7546431 - Distributed open writable snapshot copy facility using file migration policies
