Method for updating control program of physical storage devices including the steps of: selecting PSD(s) to be updated with the control program; making the PSD(s) in an off-line state; and updating the control program of the PSD(s), wherein if it needs to issue a write request to the selected PSD(s) before completion of updating the control program, unmodified data segment(s) corresponding to the write request is marked as modified data segment(s). the selected PSD(s) performs partial rebuilding after completion of updating the control program, and if it needs to read out from or write to an unmodified data segment of the selected PSD(s) before completion of the partial rebuilding, a R/W request can be issued to the PSD directly without waiting for completion of the partial rebuilding of the PSD. Multipe parity data chunks can also be provided in the same data stripe in another embodiment.