The recent rapid growth in the cloud storage industry has strongly increased the demand for high-capacity enterprise hard disk drives (HDDs). Increasing the areal density brings new challenges to the high-accuracy head-positioning control in the next generation HDD development. Triple-stage-actuator (TSA) system is one of the emerging technologies (Atsumi, 2016, “Emerging Technology for Head-Positioning System in HDDS,” IEEJ J. Ind. Appl. 5(2), pp. 117–122.) that can achieve higher bandwidth than that of a dual-stage-actuator (DSA) system and improve the track-following performance. In this paper, we focus on the TSA system with one voice coil motor (VCM) and two piezoelectric (PZT) actuators. Two types of mixed H2/H∞ synthesis methodologies based on model-based optimization and data-driven optimization are proposed to design the track-following controller for the TSA system. The simulation results show the feasibility and effectiveness of the TSA systems with a tertiary PZT actuator. We also analyze the effects of stroke limitations and resonance frequencies of the second-/third-stage PZT actuators on the head-positioning accuracy. The results might provide a guideline for the TSA mechanical design.