Patent ID: 7698521

Claim:
A processing system, comprising: a local host computer; a local storage system including a primary volume, a first communication port, and a second communication port, the local storage system receiving write requests from the local host computer via the first communication port, data associated with the write requests being written to the primary volume; a first remote storage system having a mirrored volume, a first communication port, and a second communication port, the mirrored volume having a data image that mirrors the data image of the primary volume; and a second remote storage system having a mirrored volume, a first communication port, and a second communication port, the mirrored volume having a data image that mirrors the data image of the primary volume, wherein commands are sent from the second communication port of the local storage system and received at the second communication port of the first remote storage system and at the second communication port of the second remote storage system, wherein the commands cause a copy of data corresponding to the write request to be created on the mirrored volumes respectively of the first remote storage system and the second remote storage system, wherein each of the first remote storage system and the second remote storage system has information indicating a status of the copy of the write data, wherein when the local storage system fails, one of the first or the second remote storage systems communicates to the other of the first or second remote storage systems the information indicating a status of the copy of the write data in order to identify differences between data images maintained by each of the mirrored volumes.