Abstract: A computer system is capable of recovering from a deadlock using communication gateway devices, such as a bridges, which each use a deadlock recovery mechanism. Rather than avoid deadlocks through constant monitoring of the communications path, the bridge allows the deadlock to occur. The recovery mechanisms of the bridges control the resolution of the deadlock. In one embodiment, the recovery mechanism within each bridge causes the local device which controls its bridge to disconnect. Additionally, the bridges terminate their requests for control of each other, thereby breaking the deadlock and allowing communications to resume. In another embodiment, the recovery mechanism within each bridge terminates the bridge's request for control of the other bridge. Additionally, the recovery mechanisms cause the bridges to become idle in accordance with a time delay value. The bridge with the shorter delay becomes active first and takes control of the communication path, thereby breaking the deadlock.

Abstract: A disaster tolerant computer system for protection of electronic databases is achieved by cascading storage controllers to accomplish local and remote disk shadowing. A host computer is connected to a local superordinate storage controller via a local data bus. The superordinate storage controller transmits data via a long haul data link to a remote subordinate storage controller. Additionally, the superordinate controller transmits data to a local subordinate storage controller via a local data bus. Consequently, in-band storage capacity is provided remotely, as well as locally, to increase data storage capacity for database shadowing. Furthermore, the cascading of controllers may be used to increase the effective storage capacity of the computer system by using the increased storage capacity for the writing of non-redundant data.