Servo regions are re-magnetized in the present invention. A magnetic storage device measures a first amount which is indicative of the magnitude of magnetization of a servo region, by a read head portion. The first amount may be a reproduced output, or an inverse of a gain used in an automatic gain control, etc. Servo regions are re-magnetized by a write head portion, when a servo region is detected in which a ratio of the measured first amount to an initial value of the first amount is smaller than a predetermined value, i.e., it is determined that the magnetization is reduced.

 
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> Disk drive with phase-quadrature servo pattern and demodulated position error signal insensitive to timing and phase-misalignment errors

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