Importance

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Abstract

A disaster recovery system providing remote data shadowing between a primary and a secondary site uses a method and apparatus for swapping, or switching, host directed I/O operations from a primary data storage device to a secondary data storage device in a remote copy duplex pair. Application programs running in a host processor at the primary site first quiesce all I/O operations and record updates targeted to the primary data storage device. The remote copy duplex pair is checked to verify that the secondary data storage device is a fully synchronized copy of the primary data storage device. The secondary data storage device is then swapped with the primary data storage device by terminating the remote copy duplex pair, establishing an opposite direction remote copy duplex pair such that the secondary data storage device is a primary device of the duplex pair and the primary data storage device is a shadowing device, and updating the application programs running in the primary host processor with a device address of the secondary data storage device substituted as a device address of the primary data storage device. Finally, the primary host processor resumes its application programs such that subsequent I/O operations and record updates targeted for the primary data storage device are directed through a secondary storage controller to the secondary data storage device, and copied to the primary data storage device.

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First Claim