A method of writing servo data onto a disk is disclosed. A spindle motor spins the disk, and a back electromotive force (BEMF) signal is measured from the spindle motor. A repeatable phase error (RPE) is extracted from the BEMF signal to generate an adjusted BEMF signal. A servo write clock is synchronized in response to the adjusted BEMF signal, and the servo data is written to the disk using the servo write clock. In one embodiment, the servo data comprises spiral seed patterns that are processed to write concentric servo sectors to the disk.