This patent application is assigned to Hgst Netherlands B.v.
The following quote was obtained by the news editors from the background information supplied by the inventors: "Rotating data-storage devices, commonly referred to as hard disk drives (HDD), read and write information along concentric tracks formed on disks. To navigate to a particular track on a disk, disk drives may use servo fields on the disk. These fields are utilized by a servo subsystem to position a head over a particular track. Servo writers write the servo fields onto the disk in tracks when the disk drive is manufactured and these fields are then accessed by the disk drive to determine position. Hereinafter, the path defined by the servo fields shall be referred to as the 'servo track' to distinguish it from a data track. Ideally, a head following the center of a servo track moves along a perfectly circular path around the disk. In such an ideal case, the servo track and data track would be identical.
"In reality, however, as a head attempts to follow a track it will not follow a perfect circular path. Instead, the head will deviate from the desired circular path due to a variety of factors including disk irregularity, disk eccentricity, and/or misalignments of the spindle axis assembly. This deviation from the desired path is referred to as 'runout.' Repeatable runout (RRO) refers to deviation that is non-random and occurs with some predictability. During disk drive manufacture, RRO can be measured and corresponding RRO offset values can be determined. Such RRO correction data can be generated for each track, or even each sector, and then stored on the disk within the servo pattern.
"There are two types of RRO, synchronous RRO and Non-synchronous RRO. Synchronous RRO has minimal variation from track to track and is predictable. It can usually be easily compensated for through calibration factors applied globally to the entire disk. These global calibration factors are often stored in the reserved area of the disk. Non-synchronous RRO is more problematic because it is unpredictable and varies from track to track. It is corrected through RRO correction data generated for each track or sector and typically stored on the disk in the same area as the servo pattern for each track sector. When the HDD is operational, the correctional data is read and applied in the servo-control loop.
"Determining the offset values for each sector and writing the RRO data to the RRO field portion of the individual sector servo patterns is a very time consuming process. Because the data is stored within each track sector, the RRO data takes up disk surface area that could be used to store user data. Typically about 20-50% of the servo sector overhead is for RRO data. Further, the RRO data is also spread out, so there is no efficient way to compress all of the RRO data to save on disk space.
"Accordingly there is a need for an improved method to compensate for storing and accessing non-synchronous RRO data."
In addition to the background information obtained for this patent application, VerticalNews journalists also obtained the inventors' summary information for this patent application: "Preferred embodiments of the present invention are directed at a method of correcting repeatable run out (RRO) errors for a HDD in which RRO data is instead stored in consolidated form within the reserved area of the disk, instead of storing RRO data in the servo patterns for each HDD track or sector. RRO data is preferably stored in reserved area of hard disk drive in compressed form. The compressed RRO data is subsequently read into DRAM in compressed form and then decompressed for use. Predictive techniques determine what compressed RRO-data is needed for upcoming read/write operations.
"In some preferred embodiments, shingled magnetic recording (SMR) is utilized with data written in a shingled fashion so that data writes are predictable and deterministic. RRO data, which is used to control write operations, can be prefetched from the reserved area (RA) to dynamic random access memory (DRAM) so that it will be ready when needed. The sequential nature of SMR write operations means that a relatively small data cache can be used. When RRO-data is needed to write specific tracks, data can be decompressed on the fly to reduce latency.
"The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter. It should be appreciated by those skilled in the art that the conception and specific embodiments disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
"FIG. 1A is a view of an ideal servo track on a magnetic disk.
"FIG. 1B illustrates two adjacent ideal servo track paths on the magnetic disk of FIG. 1A.
"FIG. 2A is a view of an actual servo track on a magnetic disk.
"FIG. 2B illustrates two adjacent non-ideal tracks on the magnetic disk of FIG. 2A.
"FIG. 3 shows a block diagram illustrating the basic types of errors that can affect the head position in an HDD servo system.
"FIG. 4 is a schematic illustration of a HDD surface layout 400 for a SMR drive that can be used to practice preferred embodiments of the present invention.
"FIG. 5 shows an example of a look-up table format that could be used according to preferred embodiments of the present invention.
"FIGS. 6A and 6B show a RA entry for header information and a RA entry for data information according to a preferred embodiment of the present invention.
"FIG. 7 is a flowchart showing the process of retrieving and decompressing RRO data according to preferred embodiments of the present invention.
"FIG. 8 shows a prior art hard disk drive assembly suitable for use with embodiments of the present invention.
"The accompanying drawings are not intended to be drawn to scale. In the drawings, each identical or nearly identical component that is illustrated in various figures is represented by a like numeral. For purposes of clarity, not every component may be labeled in every drawing."
URL and more information on this patent application, see: Coker, Jonathan D.; Furlong,
Keywords for this news article include: Hgst Netherlands B.v.
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