In hierarchical computer storage systems, fast and intensively used storage are paired with arrays of slower and less frequently accessed data devices. One example of high-speed, expensive memory is a direct access storage device file buffer (DASD). Slower storage devices include tape drives and disk drive arrays, which are less expensive than a DASD.
One such hierarchical storage system is a virtual tape storage system. Such a virtual tape storage system may include, for example, one or more virtual tape servers (“VTS”) in combination with one or more data storage and retrieval systems, such as the IBM TotalStorage® 3494 Enterprise Tape Library. During operation, each virtual tape storage system is communicating data from one or more hosts, and is providing data to a second VTS for copying.
Data disaster recovery solutions include various “peer-to-peer” copy routines where data is backed-up not only remotely, but also continuously (either synchronously or asynchronously). In order to communicate duplexed data from one host processor to another host processor, or from one storage controller to another storage controller, or some combination thereof, a substantial amount of control data is required for realizing the process. A high overhead, however, can interfere with a secondary site's ability to keep up with a primary site's processing, thus threatening the ability of the secondary site to be able to recover the primary in the event a disaster occurs.
Disaster recovery protection for the typical data processing system requires that primary data stored on primary DASDs be backed-up at a secondary or remote location. The physical distance separating the primary and secondary locations can be set depending upon the level of risk acceptable to the user, and can vary from several kilometers to thousands of kilometers.
Using prior art methods, in the case where, if the peer-to-peer subsystems, i.e. both virtual tape servers, are shutdown for normal service, and for some reason only one of those virtual tape servers becomes operational, then the peer-to-peer cluster must wait until both tape servers are again operational before going online to the host computer. Therefore using these prior art methods, if a second virtual tape server fails while the first virtual tape server is shutdown for maintenance, then the entire peer-to-peer system becomes unavailable until both virtual tape servers are again operational.
What is needed is a method to distribute information about the status of a peer-to-peer data storage system across a plurality of system components such that the system itself can use that stored system information to return to operation even if all the virtual tape servers are not operational.