A method of recovery from a data storage system failure in a data storage system having a host computer writing data to a first storage unit with a first storage controller synchronously mirroring the data to a second storage unit, and with a second storage controller asynchronously mirroring the data...http://www.google.de/patents/US7512835?utm_source=gb-gplus-sharePatent US7512835 - Method, system and article of manufacture for recovery from a failure in a cascading PPRC system
