The system for controlling access to data in a shared disk parallel data file comprising means (6.1, 6.8, 6.3) to determine communication failure to one node in a two node system, means (6.1,6.8) to determine whether said failed node has been enabled for a single node quorum operation, and means (6.1,6.8, 6.5) to fence data access from said failed node, upon detection of a single node enabled status. The system is provided for continuing node operations in quorum-based protocols. This is particularly valuable in the situation in which a group of nodes comprises only two nodes and in which communications to a node is lost. Provision is made for adding additional status indications to each node indicating whether or not it is enabled for single-node quorum operation. Provision is also made for identifying one node as a primary node and another node as a secondary node for time-out response purposes.
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