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Data synchronization of multiple remote storage
| Details |
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Inventors: Watanabe, Naoki;
Assignee: Hitachi, Ltd. (JP)
Primary Examiner: Sparks; Donald
Assistant Examiner: Chace; Christian P.
Attorney, Agent or Firm: Townsend and Townsend and Crew LLP
A processing system includes a local or local storage and a number of remote or remote storage systems that store data mirroring that maintained by the local storage system. Data that is written, changed, deleted or other wise modified by the local storage system is periodically sent to the remote storage systems via remote copy commands to update the mirroring data maintained by each. Failure of a local or a remote storage system will cause the surviving storage systems to exchange information indicative of the data maintained by each, and if differences exist, to exchange data so that the mirrored and/or mirroring data is the same. |
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DETAILED DESCRIPTION The present invention provides a method, and architecture for implementing that method, of synchronizing two or more remote or remote data storage facilities so that they hold and maintain the same data images in the event of a failure of the local storage.
Broadly, the invention pertains to a data processing system comprising a local (local) data storage facility communicatively coupled to (i.
e.
in communication with) two or more remote or remote storage facilities.
Each of the remote storage facilities, whether local or remote, includes storage media data storage.
Data maintained on the storage media at the local data storage facility is mirrored on storage media at the remote storage facilities.
Changes to the data image of the local storage facility are periodically sent to the remote storage facilities for updating their date images using a remote copy process that sends data messages with the data updates.
Each of the storage facilities keeps information that is indicative of the history of what updates have been received by the remote storage facilities and what updates have been received and implemented (by writes to the storage medial of such remote storage facility).
In the event of failure of a storage facility, the surviving storage facilities circulate the historical update to determine any differences, if any, of the data images, i.
e.
, have there been updates not received by any of the surviving storage facilities.
If so, the surviving storage facilities will synchronize their data images so that all have a substantially identical data image.
According to one embodiment of the invention, synchronization is achieved by a "roll-forward" operation in which that remote storage facility having the latest updates, as indicated by the historical update information, sends those needed updates to the other remote storage facilities for bring up to date all data images.
In another "roll-back" operation of synchronization, updates are discarded to bring all data images back to the same level
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Fault Detection 
