Acoustic filters for use in an ink jet print head are disclosed. When data to be transferred such as backup is transferred between SAN storing units to back up the data stored in the SAN, a data transfer instruction is sent to the transfer source and transfer destination of the data transfer via a network which is different from the SAN. The MMU is configured and arranged to read first data from the main memory arrangement in response to a stored first value associated with the first data and indicative of a start time.