The invention relates to a method, a storage subsystem and system for improving data writing efficiency. When writing data, if a predetermined N number of data or fewer than the predetermined N number of data are yet written after waiting a specific time period, the data writing I/O request is regarded as completed. The corresponding resources are then released. The N number of yet written data and the related writing information are stored in a non-volatile memory (NVRAM), so that when there is a sudden power cut or power failure happens that interrupts the data writing, the process can be resumed after the power supply is turned back on.