According to one embodiment, a magnetic disk device including a disk, a head which writes data to the disk and reads data from the disk, and a controller which sets a first DOL for a first sector group and a second DOL for a second sector group to different values, the first sector group including one or more first sectors and a first parity sector, the first sectors which allow an error correction process to be performed for each track based on the first parity sector, and are continuously arranged in a circumferential direction of the disk from the first parity sector, the second sector group including one or more second sectors which allow no error correction process to be performed for each track, and are continuously arranged in the circumferential direction.

Systems and methods are disclosed for implementing unequal error correction code (ECC) in multi-track recording. A device may comprise a circuit configured to implement an error correction coding scheme applying different code rate error correction codes on adjacent tracks within a same recording zone. The circuit may perform a read operation, including simultaneously detecting bits from a first track and a second track of the adjacent tracks, iteratively applying detected bits from the first track to perform adjacent track interference cancellation (ATIC) to decode bits from the second track, and iteratively applying detected bits from the second track to perform ATIC to decode bits from the first track.

According to one embodiment, a magnetic disk device includes a disk including two first servo sectors and at least a second servo sector, a head, and a controller, wherein the first servo sector includes burst data and a first data pattern written before the circumferential direction of the burst data, the second servo sector includes the burst data, the first data pattern, and a second data pattern written after the circumferential direction of the burst data, a first frequency of the first data pattern is different from a second frequency of the second data pattern, and a first length of the first data pattern is different from a second length of the second data pattern.

One embodiment provides a system which facilitates data movement. The system allocates, in a volatile memory of a first storage drive, a first region to be accessed directly by a second storage drive or a first NIC. The first storage drive, the second storage drive, and the first NIC are associated with a first server. The system stores data in the first region. Responsive to receiving a first request from the second storage drive to read the data, the system transmits, by the first storage drive to the second storage drive, the data stored in the first region while bypassing a system memory of the first server. Responsive to receiving, from a third storage drive associated with a second server, a second request to read the data, the system retrieves, by the first NIC, the data stored in the first region while bypassing the system memory of the first server.

One embodiment provides a system which facilitates data movement. The system allocates, in a volatile memory of a first storage drive, a first region to be accessed directly by a second storage drive or a first NIC. The first storage drive, the second storage drive, and the first NIC are associated with a first server. The system stores data in the first region. Responsive to receiving a first request from the second storage drive to read the data, the system transmits, by the first storage drive to the second storage drive, the data stored in the first region while bypassing a system memory of the first server. Responsive to receiving, from a third storage drive associated with a second server, a second request to read the data, the system retrieves, by the first NIC, the data stored in the first region while bypassing the system memory of the first server.

According to one embodiment, a magnetic disk device includes a disk including two first servo sectors and at least a second servo sector, a head, and a controller, wherein the first servo sector includes burst data and a first data pattern written before the circumferential direction of the burst data, the second servo sector includes the burst data, the first data pattern, and a second data pattern written after the circumferential direction of the burst data, a first frequency of the first data pattern is different from a second frequency of the second data pattern, and a first length of the first data pattern is different from a second length of the second data pattern.

The present disclosure is directed to a data storage device that includes a refresh monitor based on a learning based feedback control. The refresh monitor is used to control refresh operations to account for effects of writes to media, e.g., adjacent track interference (ATI). Read operations are analyzed to derive damage information usable to update one or more probability distributions, upon which the learning is updated or reinforced and carried forward. In one embodiments, the data storage device includes control circuitry configured to maintain a refresh monitor based on a learning system, analyze a read operation with the refresh monitor; adjust the refresh monitor by updating the one or more probability distributions based on the analyzed read operation; and execute a refresh operation to refresh data based on the adjusted refresh monitor.

According to one embodiment, a magnetic disk device including a disk, a head which writes data to the disk and reads data from the disk, and a controller which sets a first DOL for a first sector group and a second DOL for a second sector group to different values, the first sector group including one or more first sectors and a first parity sector, the first sectors which allow an error correction process to be performed for each track based on the first parity sector, and are continuously arranged in a circumferential direction of the disk from the first parity sector, the second sector group including one or more second sectors which allow no error correction process to be performed for each track, and are continuously arranged in the circumferential direction.

A method of recovering data from one or more failed data sectors includes estimating a reader offset position from a first or a second read attempt of the one or more failed data sectors at a current set of channel parameters and basing the estimated reader offset position on, at least in part, a position error signal generated during the first or second read attempt. At least one read is performed on the one or more failed data sectors at the estimated reader offset position to obtain one or more samples. The one or more samples are processed to obtain a processed sample. Iterative outer code recovery is performed on the processed sample.

Techniques perform data access to a disk array. The disk array includes a parity disk and a plurality of data disks. Via such techniques, data is written to the parity disk in the disk array in response to a write request to a failed data disk in the disk array when the disk array is in a degraded state; and corresponding degraded storage position information is set in disk resource mapping information so as to indicate that the data are stored in the parity disk. Accordingly, enormous computing resources can be saved, and I/O operations required by reads in the degraded state can be reduced.