A method of creating a multiple of virtual Serial Advanced Technology Attachment ports in a disk array controller, and the method builds a port multiplier in a Serial Advanced Technology Attachment disk array controller by a software method, and the port multiplier defines several slices capable of identifying the address of a computer host system. The port multiplier is connected to at least one disk set, and each disk is divided into several data blocks corresponding to data blocks of another disk of the same disk set to constitute a synchronously updated disk backup system. The software method provides a method of connecting several storage units to overcome the restriction on the point-to-point connection of the Serial Advanced Technology Attachment disk array system, so as to achieve a multi-driving function and a serial bus system.