Disk drive selecting head for write operation based on environmental condition

Description

BACKGROUND

Description of the Related Art

Disk drives comprise a disk and a head connected to a distal end of an actuator arm which is rotated about a pivot by a voice coil motor (VCM) to position the head radially over the disk. The disk comprises a plurality of radially spaced, concentric tracks for recording user data sectors and embedded servo sectors. The embedded servo sectors comprise head positioning information (e.g., a track address) which is read by the head and processed by a servo controller to control the velocity of the actuator arm as it seeks from track to track.

FIG. 1 shows a prior art disk format 2 comprising a number of data tracks 4 defined by concentric servo sectors 6₀-6_N recorded around the circumference of each data track. Each servo sector 6_i comprises a preamble 8 for storing a periodic pattern, which allows proper gain adjustment and timing synchronization of the read signal, and a sync mark 10 for storing a special pattern used to synchronize to a servo data field 12. The servo data field 12 stores coarse head positioning information, such as a servo track address, used to position the head over a target data track during a seek operation. Each servo sector 6_i further comprises groups of servo bursts 14 (e.g., A, B, C and D bursts), which comprise a number of consecutive transitions recorded at precise intervals and offsets with respect to a data track centerline. The groups of servo bursts 14 provide fine head position information used for centerline tracking while accessing a data track during write/read operations.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a prior art disk format comprising a plurality of data tracks defined by embedded servo sectors.

FIGS. 2A and 2B show a disk drive according to an embodiment of the present invention comprising a plurality of disks and a head actuated over each disk surface.

FIG. 2C is a flow diagram according to an embodiment of the present invention wherein when a write command is received the disk surface to write is selected based on a measured environmental condition.

FIG. 2D shows an embodiment of the present invention wherein dynamic logical block address (LBA) mapping is implemented using a circular buffer.

FIG. 3A is a flow diagram according to an embodiment of the present invention wherein when the environmental conditions are within nominal limits the data is copied from a first disk surface to a second disk surface in order to free space on the first disk surface.

FIG. 3B is a flow diagram according to an embodiment of the present invention wherein the data is copied to a second disk surface during a garbage collection operation.

FIGS. 4A and 4B shows an embodiment of the present invention wherein the first disk surface may comprise a lower radial and/or linear density for writing data during extreme environmental conditions.

FIGS. 5A and 5B show a disk drive according to an embodiment of the present invention wherein when a write command is received, an area of a disk surface is selected based on a measured ambient temperature.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

FIGS. 2A and 2B show a disk drive according to an embodiment of the present invention comprising a plurality of disk surfaces 18₀-18_N and a head 16₀-16_N actuated over each disk surface. The disk drive further comprises control circuitry 20 operable to execute the flow diagram of FIG. 2C, wherein when a write command is received (step 22), an environmental condition is measured (step 24) and a disk surface to write the data is selected based on the measured environmental condition (step 26).

In the embodiment of FIG. 2A, each disk surface 18, comprises a plurality of servo sectors 28₀-28_N that define a plurality of data tracks 30, wherein each data track comprises a plurality of data sectors. The control circuitry 20 processes a read signal 32 to demodulate the servo sectors into a position error signal (PES). The PES is filtered with a suitable compensation filter to generate a control signal 34 applied to a voice coil of a voice coil motor (VCM) 36 which rotates an actuator arm 38 about a pivot to position the head radially over the disk surface in a direction that reduces the PES.

In one embodiment, the data sectors on each disk surface are accessed indirectly by mapping a logical block address (LBA) to a physical block address (PBA) mapped to a data sector. The LBA to PBA mapping facilitates mapping out defective data sectors by mapping out the corresponding PBAs. In one embodiment, the LBA to PBA mapping also facilitates dynamic LBA mapping wherein the LBAs of a write command are dynamically mapped to PBAs of a selected disk surface when the write command is executed. In this manner, the disk surface may be selected that provides the best performance relative to a measured environmental condition (e.g., temperature, pressure, etc.).

Dynamic LBA mapping may be implemented in any suitable manner in the embodiments of the present invention. In one embodiment illustrated in FIG. 2D, dynamic LBA mapping is implemented using one or more a circular buffers of PBAs on each disk surface. New data is written to the circular buffer head (CBH) and the LBAs mapped to the corresponding PBAs. When an LBA is overwritten, the PBA storing the old data toward the circular buffer tail is invalidated so that it may be overwritten. A garbage collection operation may be executed periodically to relocate the fragmented valid data sectors from the circular buffer tail to the circular buffer head so that the tail may be overwritten as a consecutive sequence of data sectors. Techniques other than a circular buffer may be employed to implement dynamic LBA mapping in the embodiments of the present invention.

In one embodiment, the sensitivity of each head 16₀-16_N and/or each disk surface 18₀-18_N may vary due to tolerances in manufacturing and materials. In addition, varying environmental conditions (temperature, pressure, etc.) may have an adverse affect on the sensitivity of the head/disk interfaces. Accordingly, each head/disk interface may exhibit a different level of performance (bit error rate, signal-to-noise ratio, etc.) depending on the environmental conditions at the time of a write operation. In one embodiment, if a measured environmental condition exceeds a threshold, a disk surface having a higher reliability is selected to perform the write operation (e.g., a disk surface having a higher head/disk sensitivity, or in another embodiment, a disk surface having a lower recording density).

In one embodiment, the heads 16₀-16_N in the disk drive may be tested over different environmental conditions so that a correlation can be established and the appropriate disk surface selected during each write operation. Any suitable test may be executed to measure the performance of each head at varying environmental conditions, such as measuring a bit error rate when writing/reading a test pattern, or by measuring an off-track read capability of each head. The heads may be tested during a manufacturing procedure of each disk drive and/or periodically while the disk drive is in the field. An embodiment of this invention is illustrated in the flow diagram of FIG. 3A wherein the heads are tested relative to different environmental conditions to establish the correlation (step 40). When a write command is received comprising an LBA (step 42), an environmental condition(s) is measured (step 44) and a disk surface is selected in response to the measured environmental condition (step 46). The data is written to the head of a circular buffer on the selected disk surface (step 48), and the LBA is mapped to a PBA at the circular buffer head (step 50).

In one embodiment, a frequently written disk surface during extreme environmental conditions may approach its capacity limit. In one embodiment, when the high reliability disk surface nears its capacity, and the disk drive is operating under nominal environmental conditions, data is relocated from the high reliability disk surface to one or more of the other disk surfaces in order to free space on the high reliability disk surface.

This embodiment is illustrated the flow diagram of FIG. 3A wherein when a decision is made to relocate data from a first disk surface (step 52), a second disk surface is selected to store the relocated data (step 54). The second disk surface may be selected based on any suitable criteria, such as the amount of free space and/or a current state of a measured environmental condition. Data is read from the first disk surface (step 56) and written to the head of a circular buffer on the second disk surface (step 58). The corresponding LBAs are mapped to the PBAs at the head of the circular buffer on the second disk surface (step 60).

In an embodiment illustrated in the flow diagram of FIG. 3B, the decision to relocate data from a first disk surface to a second disk surface occurs when executing a garbage collection operation on the first disk surface (step 62). The garbage collection operation relocates fragmented valid data so that the invalid data sectors can be overwritten as a consecutive sequence. During the garbage collection operation, valid data is read from the first disk surface (step 64) and written to the head of a circular buffer on a second disk surface (step 66). In one embodiment, the valid data is relocated to the second disk surface if the environmental conditions are conducive to writing to the second disk surface. Otherwise, the valid data may be rewritten to the first disk surface (e.g., written to a head of a circular buffer on the first disk surface). The garbage collection operation may be performed at any suitable time, including periodically, or when the amount of fragmented valid data exceeds a threshold. In one embodiment, the garbage collection operation may be deferred until the environmental conditions are conducive to relocating data to a second disk surface.

In one embodiment, data is written to one or more of the disk surfaces at a lower recording density to improve reliability under extreme environmental conditions. An example of this embodiment is shown in FIG. 4A wherein the radial density (data tracks per inch) and/or the linear density (data rate of the data sectors) of a first disk surface is reduced compared to the disk surface shown in FIG. 4B. Because the disk surface of FIG. 4A has a lower recording density, it also has less capacity and therefore fills up faster than the other disk surfaces. Accordingly, in one embodiment when the environmental conditions are within nominal limits, the data is relocated from the lower density disk surface to a higher density disk surface.

FIG. 5A shows a disk drive according to an embodiment of the present invention comprising a head 16 actuated over a disk surface 18 and control circuitry 20 operable to execute the flow diagram of FIG. 5B. When a write command is received comprising write data (step 68), an ambient temperature of the disk drive is measured (step 70). An area of the disk surface is then selected to write the data in response to the measured ambient temperature (step 72). For example, at extreme ambient temperatures (hot or cold) the data may be written more reliably at a particular radial location (e.g., inner, middle, or outer diameter tracks). Similar to the embodiments described above, data may eventually be migrated to other areas of the disk surface (or to a different disk surface) when the ambient temperature is within nominal limits.

Any suitable control circuitry may be employed to implement the flow diagrams in the embodiments of the present invention, such as any suitable integrated circuit or circuits. For example, the control circuitry may be implemented within a read channel integrated circuit, or in a component separate from the read channel, such as a disk controller, or certain steps described above may be performed by a read channel and others by a disk controller. In one embodiment, the read channel and disk controller are implemented as separate integrated circuits, and in an alternative embodiment they are fabricated into a single integrated circuit or system on a chip (SOC). In addition, the control circuitry may include a suitable preamp circuit implemented as a separate integrated circuit, integrated into the read channel or disk controller circuit, or integrated into an SOC.

In one embodiment, the control circuitry comprises a microprocessor executing instructions, the instructions being operable to cause the microprocessor to perform the steps of the flow diagrams described herein. The instructions may be stored in any computer-readable medium. In one embodiment, they may be stored on a non-volatile semiconductor memory external to the microprocessor, or integrated with the microprocessor in a SOC. In another embodiment, the instructions are stored on the disk and read into a volatile semiconductor memory when the disk drive is powered on. In yet another embodiment, the control circuitry comprises suitable logic circuitry, such as state machine circuitry.