Various illustrative aspects are directed to a data storage device, comprising one or more disks; an actuator mechanism configured to position one or more heads proximate to a corresponding disk surface of the one or more disks; and one or more processing devices. The one or more processing devices are configured to apply a pre-bias current to the assistive energy emitter at a first value while the selected head is positioned proximate to one or more spiral patterns on the corresponding disk surface. The one or more processing devices are further configured to apply the pre-bias current to the assistive energy emitter at a boosted value while the selected head is not positioned proximate to the one or more spiral patterns, wherein the boosted value is greater than the first value.

During in-drive writing of a servo spiral on a disk surface, a servo spiral can be distinguished during demodulation from adjacent servo spirals on the same disk surface. When a set of servo spirals is written on a disk surface, a first spiral is written to include a first identifying characteristic and the following spiral is written to include a second identifying characteristic. The identifying characteristic may include embedded sync marks encoding a certain numerical value, a unique frequency of high-low transitions included in each spiral, and/or a unique frame size.

A hard disk drive (HDD) is configured to move a read head over a region of a storage surface that includes unreadable segments of reference spirals that have been overwritten by a reference spiral in a set of spirals that is currently being written on the storage surface. By moving the read head across the region of the storage surface at a return radial velocity that is selected such that the write head crosses no consecutive reference spirals at an unreadable segment, the servo system of the HDD does not experience an error due to crossing multiple consecutive reference spirals at unreadable segments. Thus, a set of spirals that includes partially damaged reference spirals can be employed to control the position of a read head. Consequently, a second surface is not required for the set of spirals employed in controlling the writing process.

During in-drive writing of a servo spiral on a disk surface, a servo spiral can be distinguished during demodulation from adjacent servo spirals on the same disk surface. When a set of servo spirals is written on a disk surface, a first spiral is written to include a first identifying characteristic and the following spiral is written to include a second identifying characteristic. The identifying characteristic may include embedded sync marks encoding a certain numerical value, a unique frequency of high-low transitions included in each spiral, and/or a unique frame size.

A hard disk drive (HDD) is configured to move a read head over a region of a storage surface that includes unreadable segments of reference spirals that have been overwritten by a reference spiral in a set of spirals that is currently being written on the storage surface. By moving the read head across the region of the storage surface at a return radial velocity that is selected such that the write head crosses no consecutive reference spirals at an unreadable segment, the servo system of the HDD does not experience an error due to crossing multiple consecutive reference spirals at unreadable segments. Thus, a set of spirals that includes partially damaged reference spirals can be employed to control the position of a read head. Consequently, a second surface is not required for the set of spirals employed in controlling the writing process.

A system includes a controller and a detector. The controller is configured to read servo spirals written on a magnetic surface of a disk drive. The servo spirals are written on the magnetic surface of the disk drive based on seed wedges. The seed wedges are written on the magnetic surface of the disk drive prior to writing the servo spirals on the magnetic surface of the disk drive. The controller is configured to write a servo pattern on the magnetic surface of the disk drive based on reading the servo spirals written on the magnetic surface of the disk drive. The detector is configured to detect, while reading the servo spiral written on the magnetic surface of the disk drive, interference caused by the seed wedges written on the magnetic surface of the disk drive.

A data storage device comprising a head actuated over a disk comprising a plurality of tracks. The head is positioned over a target track, and a sampled position error signal (PES) is generated representing a position of the head relative to the target track. The sampled PES is filtered with a servo compensator to generate a sampled control signal, and the sampled control signal is upsampled to generate an upsampled control signal. The sampled PES is upsampled to generate an upsampled PES, and the upsampled PES is processed to generate compensation values. The upsampled control signal is combined with the compensation values to generate a compensated control signal, and the position of the head over the target track is adjusted based on the compensated control signal.

A repeatable runout (RRO) is accurately compensated for while moving a magnetic head radially across a disk surface. An iterative learning control algorithm is employed to determine appropriate feed-forward coefficients for an RRO compensation signal for each of a plurality of radial locations across the disk surface. The feed-forward coefficients are determined by performing multiple iterations of continuously moving the magnetic head across the disk surface along a target path while measuring a position error signal that indicates the radial error between the magnetic head and the target path. With each iteration, the iterative learning control algorithm computes new feed-forward coefficients for each of the plurality of radial locations, where the new feed-forward coefficients are selected to reduce the measured position error signal when employed to move the magnetic head along the target path.

A repeatable runout (RRO) is accurately compensated for while moving a magnetic head radially across a disk surface. An iterative learning control algorithm is employed to determine appropriate feed-forward coefficients for an RRO compensation signal for each of a plurality of radial locations across the disk surface. The feed-forward coefficients are determined by performing multiple iterations of continuously moving the magnetic head across the disk surface along a target path while measuring a position error signal that indicates the radial error between the magnetic head and the target path. With each iteration, the iterative learning control algorithm computes new feed-forward coefficients for each of the plurality of radial locations, where the new feed-forward coefficients are selected to reduce the measured position error signal when employed to move the magnetic head along the target path.

A method of writing servo spirals for spiral-based self-servo writing includes determining control parameters for controlling movement of a write head between a first and a second disk radial location at a first velocity, writing a first spiral while controlling the movement of the write head between the first and the second disk radial location at the first velocity according to the determined control parameters, writing a second spiral while controlling movement of the write head between the first and the second disk radial location at a second velocity that is different from the first velocity, based on timing and location information from the first spiral, and writing a third spiral while controlling movement of the write head between the first and the second disk radial location at the first velocity according to the determined control parameters and based on timing and location information from the second spiral.