Patent ID: 7904743

Claim:
A computer readable storage medium, wherein code stored in the computer readable storage medium when executed by a processor causes operations to be performed, the operations comprising: receiving, at a primary controller, a request from a primary host, to set reservations on a primary storage and a secondary storage, wherein the primary host, the primary controller and the primary storage are at a first site, and wherein a secondary host, a secondary controller, and the secondary storage are at a second site, wherein the primary host is coupled to the primary controller via a first local area network at the first site, and the secondary host is coupled to the secondary controller via a second local area network at the second site; setting, by the primary controller, a first reservation on the secondary storage via a storage area network coupling the secondary storage to the primary controller, wherein the setting of the first reservation causes the secondary storage to be read only for a secondary host and wherein the setting of the first reservation prevents the secondary storage to be read from or written onto by the primary host; and setting, by the primary controller, a second reservation on the primary storage, wherein the setting of the second reservation allows the primary host to perform read and write operations on the primary storage, wherein the setting of the second reservation prevents the primary storage to be read from or written onto by the secondary host, wherein the storage area network is a first network, wherein the primary host is coupled to the secondary host over a second network, the operations further comprising: substituting the primary host by the secondary host, in response to: the secondary host determining over the second network that the heartbeat of the primary host is absent; and the secondary controller determining over the first network that the primary host is unable to clear a challenge reservation made by the secondary controller on the primary storage, subsequent to the secondary host determining over the second network that the heartbeat of the primary host is absent.