A computer-implemented method, system and computer program product, the method comprising: receiving a request for backing up data from a mainframe on a backup server implemented on an open system; issuing a call to data set services, the call associated with an exit function; receiving a callback to the exit function, the callback associated with a data set record; packing the data set record to obtain packed information; and transmitting the packed information over a network connection to the backup server for backing up the data, wherein no additional data is written to a persistent memory of the mainframe, and wherein no limitations exist on a number of mainframes connected to the mainframe, or on a number of mainframes simultaneously communicating with the backup server.