Abstract: Disclosed is a system, method, and program storage device implanting the method for revising a software application wherein the software application utilizes persistent data, comprising applying an upgrade to a first next level of software that understands both old and new persistent data structure formats; converting all persistent data structures into the old persistent data structure format; applying an upgrade to a second next level of software that understands the old and new persistent data structure formats; converting all persistent data structures into the new persistent data structure format; applying a downgrade to a first previous level of software that understands both the old and new persistent data structure formats; converting all persistent data structures into the old persistent data structure format; and applying a downgrade to a second previous level of software that understands the old persistent data structure formats.

Abstract: A method and apparatus are provided for detecting and correcting various data errors that may arise in a mass data storage apparatus comprising a set of physical mass storage devices operating as one or more larger logical mass storage devices. More particularly, there is provided a method and apparatus for determining, on restoration of power to a device set, whether or not a write operation was interrupted when power was removed, and for reconstructing any data that may be inconsistent because of the removal of power.