Peer-to-peer backup system with failure-triggered device switching honoring reservation of primary device

Abstract

A peer-to-peer backup storage system automatically switches from a primary storage site to a mirrored backup site in response to a primary site failure, where the secondary site then honors any existing host initiated reservation of primary storage. Each site includes a storage controller and storage, where the primary site receives and stores data and forwards the received data to the secondary site for storage to mirror contents of primary storage. The primary and secondary sites are coupled to one or more hosts. Whenever the primary controller receives a reserve request from a host, it reserves the primary storage (or a subpart thereof) for the exclusive use of the reserve-initiating host. This may involve, for example, the primary controller storing a path group ID that identifies the reserving host. The primary controller also notifies the secondary controller of the reservation, e.g., sending the path group ID involved in the reservation operation to the secondary site. Responsive to a primary site failure, the system performs “switch” operation where the system stops forwarding data from the primary site to the secondary site. Furthermore, the secondary site is operated in substitution for the primary site, to receive and store data from the hosts. Importantly, the secondary site honors the existing reservation of the primary storage by reserving the secondary storage to the first reserve-initiating host.