Abstract: A computer-implemented method operable in a computer system comprising a plurality of computers including at least a first computer and at least two second computers, the method includes: obtaining a first identifier from the first computer at the at least two second computers, said first identifier having been determined, at least in part, by applying a first function to the content of the data item, wherein the first function comprises a hash function; and at least one of the at least two second computers using the first identifier to ascertain a storage location for the data item on the computer system. At least one of the at least two second computers may use the first identifier to access the data item on the computer system. The method may include verifying that the content of the data item has not changed since creation of the first identifier.