A multi battery pack system is composed of a plurality of battery packs. Thus is produced a material for bearing parts which can satisfy the life requirements for bearings without an excessive increase in a shot time during the shot peening treatment. The primary storage array may be configured to execute inputoutput requests between the remote storage array and the primary storage array based on the adjusted queue size. Accordingly, when the optical fiber sensor is offset to the upper portion of the front-bumper reinforcement, the front-bumper absorber will not topple down and the impact load is input to the optical fiber sensor even if the input direction of the impact load is slightly inclined. A valve is provided which, when a maximum pressure level in the working lines is exceeded, the valve is reversed such that the common component reverses the stroke volumes toward a lower power consumption arrangement.