This invention discloses a storage visualization subsystem and system with host-side redundancy via SAS connectivity. The I/O interconnect interface between the storage visualization controller and the host is a serial-attached SCSI (SAS) interface. At least one SAS expander is inserted on the I/O interconnect path of the host side to provide the function of device expansion. Or, a built-in virtual SAS expander is disposed inside the storage virtualization controller to provide multiple virtual IDs for each SAS port. When one controller in the storage virtualization controller pair malfunctions or fails, the invention provides solutions in accord with different embodiments so that the surviving controller can inherit the ID of the failed one. Thus, the host can keep functioning normally as it is not aware of any change in the device status.