Abstract: A method for executing a write request in a clustered computing environment, comprising a plurality of computers connected in a network, including at least one client computer accessing data blocks stored on a first storage device of a shared aggregated pool of storage devices. Data blocks stored on the first storage device are linked to data blocks stored on at least one second storage device of the pool by error recovery data stored on a third storage device of the pool. When a client computer sends a write request to the first storage device for a new data block to be stored at an address on the first storage device, the new data block is written at the address on the first storage device. New error recovery data is calculated for the data block and is written to the third storage device.

Abstract: A method for retrieving and modifying data elements on a shared medium following request from multiple client computers, such that data retrieval transactions on a data element, originating from one or more clients, are not compromised by data update transactions on the same data element originating from other clients. The shared medium controller receives from multiple clients transaction requests for reading or writing a data element stored on the shared medium. The transactions requests are added to an execution queue in order. All read transaction requests are then retrieved and executed in parallel, up to a write transaction request on the data element. The write transaction request is then executed while all incoming read transaction requests for the same data element are queued until the write transaction request is completed.

Abstract: A method for retrieving data elements from a shared medium by a client computer is provided. The shared medium maintains a main list of data version information associated with each data element, while the client maintains another locally-stored list containing all previously retrieved data elements associated with their respective data version. The client computer checks whether there is a record for a data element in the locally-stored list and if so, sends the data version associated with it to the shared medium. The shared medium compares the data version received with the data version stored in its main list and if the two match, sends a confirmation to the client computer. If the data versions do not match, the shared medium sends a new copy of the data element and a new data version to the originating client computer, such that the client computer updates its locally-stored list.