Instrumenting a disk drive suspension with vibration sensing strain gages can enhance vibration suppression in hard disk drives, provided that the gages are properly located and are sufficiently sensitive. The cost function of an optimal LQG controller with Kalman filter is proposed as an objective function for determining the optimal location and orientation of displacement sensors on a flexible structure, such as the placement of strain gages on a disk drive suspension. Analytical bounds are derived for the Kalman filter Riccati equation in a modal system with large sensor noise. These bounds produce analytical approximations that reduce the computational complexity of the LQG optimization approach with cheap control. Results are applied to a prototype disk drive suspension to identify sensor positions and sensor requirements. Methods of installing strain gages on steel at precise locations are briefly discussed.