According to one embodiment, a magnetic disk device includes a disk including a first region with a first format efficiency and a second region with a second format efficiency lower than the first format efficiency, a head that writes data to the disk and reads data from the disk, and a controller that selects a first postcode to be written to the first region from a plurality of postcodes with different lengths and writes the first postcode to the first region, and selects a second postcode to be written to the second region from a plurality of postcodes with different lengths and writes the second postcode to the second region.

A data storage device is disclosed comprising a first plurality of heads actuated over a first subset of disk surfaces by a first servo control loop comprising a first coarse actuator and a first fine actuator, and a second plurality of heads actuated over a second subset of the disk surfaces by a second servo control loop comprising a second coarse actuator and a second fine actuator. A plurality of access commands are received, wherein each access command is associated with one of the heads. While executing a first access command using the first servo control loop, a disturbance is ramped while injecting the disturbance into the second servo control loop, and the second fine actuator is calibrated based on the disturbance.

According to one embodiment, a magnetic disk device includes a disk having a first sector including first servo data, first user data, and first correction information used to correct a data error, a head that writes data to the disk and that reads data from the disk, and a controller that changes, according to a first defect length of a defect generated in the first sector in a circumferential direction of the disk, a first sector length of the first sector in the circumferential direction.

In a disk drive, when an off-track error occurs during a sequential disk access operation that spans multiple contiguous data tracks, efficient recovery is performed. In an embodiment, the disk access operation (e.g., reading from or writing to a disk) is attempted for all sectors of the sequential disk access operation. The disk access operation is then attempted again for sectors associated with any off-track errors that occurred during the disk access operation. In another embodiment, when an off-track error occurs during a sequential write operation in a shingled magnetic recording drive, the data originally targeted to be written to a first portion is written to a second portion of the data track that follows the first portion. Since no additional revolutions of the disk are needed for data associated with the sequential write operation to be written to the disk.

According to one embodiment, a magnetic disk device including a disk, a head, and a controller configured to, when writing a first servo sector, a second servo sector, and a third servo sector in the order described according to a second route varying in a radial direction of the disk with respect to a first route, adjust first timing used to write the second servo sector next to the first servo sector, and adjust second timing used to write the third servo sector next to the second servo sector.

In a two-dimensional magnetic recording (TDMR) system, a first finite impulse response (FIR) filter processes data read from a track of a magnetic medium by a first head using first filter tap values determined a priori independently of a second head. A second FIR filter processes data read from a track by the second head using second filter tap values determined a priori independently of the first head. A read channel module generates an output based on outputs of the first and second FIR filters.

In a disk drive, when an off-track error occurs during a sequential disk access operation that spans multiple contiguous data tracks, efficient recovery is performed. In an embodiment, the disk access operation (e.g., reading from or writing to a disk) is attempted for all sectors of the sequential disk access operation. The disk access operation is then attempted again for sectors associated with any off-track errors that occurred during the disk access operation. In another embodiment, when an off-track error occurs during a sequential write operation in a shingled magnetic recording drive, the data originally targeted to be written to a first portion is written to a second portion of the data track that follows the first portion. Since no additional revolutions of the disk are needed for data associated with the sequential write operation to be written to the disk.

A method reduces the effect of accelerating/decelerating an aggressor actuator in a multi-actuator drive on a victim actuator in the drive. Measurements of fractional-wedge timing-offsets for an aggressor head are used to adjust the aggressor actuator commands that are inputted to a victim disturbance feedforward signal generator when a timing offset exists between the currently-used aggressor head and the aggressor head that was used to measure transfer functions for determining victim feedforward signals. When such a timing offset is equivalent to a specific fraction of the time period separating servo wedges, values of the aggressor actuator commands that are inputted to the victim disturbance feedforward signal generator may be modified based on the specific fraction. Feedforward signals may be modified when a timing offset exists between and the current timing of the currently-used victim head and an original timing of the currently-used victim head.

According to one embodiment, a magnetic disk device which includes two or more independently drivable actuator blocks and performs seek control with a low jerk in which a jerk that is a derivative of acceleration is limited, wherein in a state where a first actuator block is not accessing a data sector of a disk, a second actuator block that is not the first actuator block accesses the data sector of the disk by seek control with a high Jerk.

A magnetic disk device includes a magnetic disk including a track having a plurality of sectors, a motor configured to rotate the magnetic disk, a magnetic head, and a controller. The controller is configured to perform a first read operation of reading target sectors among the sectors of the track, with the magnetic head during a first revolution of the magnetic disk, detect an off-track state of the magnetic head during the first revolution of the magnetic disk, perform a first error correction with respect to data read from the target sectors during the first read operation, and perform a second read operation of selectively reading a part of the target sectors for which the off-track state has been detected or the first error correction is unsuccessful, with the magnetic head during a second revolution of the magnetic disk.