Managing access to shared data in data processing networks

DETAILED DESCRIPTION In order to address the above described deficiencies in the prior art, it is an object of the present invention to provide a mechanism that allows for shared access to storage devices by coordinating exclusive access to the storage devices.
According to a first aspect of the invention therefore, there is provided, in a data processing network including a plurality of array controllers connected for communication to each other and a plurality of data storage devices, a method for coordinating exclusive access by the plurality of controllers to a shared data region on said plurality of data storage devices.
The method comprises the steps of: for each write operation to the shared data region, sending an exclusive access request from a controller desiring such access to all controllers having access to the shared data region; and, as part of granting exclusive access to the requesting controller, storing a non-volatile record of the write operation in each of the plurality of controllers having access to the shared data region.
When viewed from a second aspect the method comprises the steps of: at a first array controller, broadcasting an exclusive access request to all other array controllers having access to the shared data region and storing a non-volatile record of the write operation in the first controller; and at each controller receiving the exclusive access request, storing a non-volatile record of the write operation prior to sending an exclusive access grant to the first controller.
Thus in contrast with the technique disclosed in WO98/28685, a method for coordinating access is provided which does not involve assigning one of the controllers as a primary controller and sending all exclusive access requests to the primary controller.
In accordance with the present invention, each controller is a peer and equivalent to all other controllers and if it requires exclusive access, it sends a request to all controllers on the network.
Those controllers which share access to the affected region then grant access to the requesting controller