Disk drive employing different zone boundaries across disk surfaces

[0001] 1. Field of the Invention

[0002] The present invention relates to disk drives for computer systems. More particularly, the present invention relates to a disk drive employing different zone boundaries across disk surfaces.

[0003] 2. Description of the Prior Art

[0004] Prior art disk drives employ one or more disks with heads actuated over the respective disk surfaces (e.g., top and bottom surfaces). Each disk surface comprises a plurality of radially spaced, concentric data tracks, wherein each data track comprises a number of data sectors for storing user data. During write operations, the disk drive receives user data and a logical block address (LBA) which is mapped to an absolute block address (ABA) identifying one of the data sectors for storing the user data. The LBA to ABA mapping enables defective data sectors to be mapped to spare data sectors.

[0005] Because the disk is rotated at a constant velocity, the data rate is typically increased toward the outer diameter tracks (where the surface of the disk is spinning faster) in order to achieve a more constant linear bit density across the radius of the disk. To simplify design considerations, the data tracks are typically banded together into a number of physical zones, wherein the data rate is constant across a zone, and increased from the inner diameter zones to the outer diameter zones. This is illustrated in FIG. 1, which shows a prior art disk format 2 comprising a number of data tracks 4, wherein the data tracks are banded together in this example to form three physical zones from the inner diameter of the disk (ZONE 1) to the outer diameter of the disk (ZONE 3). The prior art disk format of FIG. 1 also comprises a number of embedded 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 symbol synchronize to a servo data field 12. The servo data field 12 stores coarse head positioning information, such as a track address, used to position the head over a target data track during a seek operation. Each servo sector 6; 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.

[0006] Prior art disk drives typically configure the physical zones so that the zone boundaries occur at the same radial locations across all disk surfaces. However, a recent development is to optimize the size of each physical zone relative to the characteristics of each head/disk interface. In addition, the linear bit density as well as the tracks-per-inch (TPI) may be optimized for each disk surface, which can also cause the size of the physical zones (and corresponding physical zone boundaries) to differ across the disk surfaces. When the physical zone boundaries are different across the disk surfaces, a problem arises in locating the appropriate data sector corresponding to a given ABA. In other words, allowing the physical zone boundaries to vary across disk surfaces complicates the process of mapping an ABA to the corresponding physical zone, head, and data track.

[0007] There is, therefore, a need to simplify the ABA to zone/head/track mapping in a disk drive wherein the zone boundaries vary across the disk surfaces.

[0008] An embodiment of the present invention comprises a disk drive having a plurality of disk surfaces. Each disk surface comprises a plurality of data tracks, wherein each data track comprises a plurality of data sectors. The data tracks of each disk surface are banded together into a plurality of physical zones each having physical zone boundaries at predetermined radial locations on the disk surface, wherein each physical zone operable to store data in the data sectors at a predetermined data rate. A first physical zone on a first disk surface has a physical zone boundary at a first predetermined radial location, wherein the first predetermined radial location is different from any of the radial locations of the physical zone boundaries on a second disk surface. The disk drive further comprises control circuitry operable to identify a plurality of logical zones having logical zone boundaries defined relative to the physical zone boundaries of at least the first and second disk surfaces, wherein the number of logical zones is greater than the number of physical zones for at least one of the disk surfaces. The logical zones are used to find one of the data sectors corresponding to a block address received from a host.

[0009] In one embodiment, the disk drive further comprises a plurality of heads actuated over respective disk surfaces, and the data sector corresponding to the block address is located by finding the logical zone corresponding to the block address, finding the head within the logical zone corresponding to the block address, and finding the data track corresponding to the head and block address.

[0010] In another embodiment, the data sectors of one of the physical zones on a first disk surface store data at a first data rate, and the data-sectors of a corresponding physical zone on a second disk surface store data at a second data rate different than the first data rate.

[0011] In yet another embodiment, the data tracks on a first disk surface comprise a first radial density, and the data tracks on a second disk surface comprise a second radial density different than the first radial density.

[0012] In still another embodiment, each disk surface comprises a plurality of servo tracks, and on at least one of the disk surfaces the radial density of the data tracks is different than the radial density of the servo tracks. In one embodiment, the control circuitry is further operable to identify a plurality of clusters, wherein each cluster comprises a first number of servo tracks and a second number of data tracks, and the first number of servo tracks is different than the second number of data tracks. In one embodiment, the control circuitry is further operable to find the data sector corresponding to the block address by finding the logical zone corresponding to the block address, finding the cluster within the logical zone corresponding to the block address, finding the head within the cluster corresponding to the block address, and finding the data track corresponding to the head and block address. In yet another embodiment, the control circuitry is further operable to find the data sector corresponding to the block address by finding the servo track and a radial offset from the servo track that correspond to the data track.

[0013] Another embodiment of the present invention comprises a method of mapping a block address received from a host to a data sector in a disk drive, the disk drive comprising a plurality of disk surfaces. Each disk surface comprises a plurality of data tracks, wherein each data track comprises a plurality of data sectors. The data tracks of each disk surface are banded together into a plurality of physical zones each having physical zone boundaries at predetermined radial locations on the disk surface, wherein each physical zone operable to store data in the data sectors at a predetermined data rate. A first physical zone on a first disk surface has a physical zone boundary at a first predetermined radial location, wherein the first predetermined radial location is different from any of the radial locations of the physical zone boundaries on a second disk surface. The method comprises the steps of identifying a plurality of logical zones having logical zone boundaries defined relative to the physical zone boundaries of at least the first and second disk surfaces, wherein the number of logical zones is greater than the number of physical zones for at least one of the disk surfaces. The logical zones are used to find one of the data sectors corresponding to the block address received from the host.

[0021] FIGS. 2A and 2B show a disk drive according to an embodiment of the present invention having a plurality of disk surfaces (16₀-16₃). Each disk surface (e.g., disk surface 16₀) comprises a plurality of data tracks 18, wherein each data track comprises a plurality of data sectors. The data tracks 18 of each disk surface are banded together into a plurality of physical zones each having physical zone boundaries at predetermined radial locations on the disk surface, wherein each physical zone is operable to store data in the data sectors at a predetermined data rate. A first physical zone on a first disk surface has a physical zone boundary at a first predetermined radial location, wherein the first predetermined radial location is different from any of the radial locations of the physical zone boundaries on a second disk surface. The disk drive further comprises control circuitry 20 operable to identify a plurality of logical zones having logical zone boundaries defined relative to the physical zone boundaries of at least the first and second disk surfaces, wherein the number of logical zones is greater than the number of physical zones for at least one of the disk surfaces. The logical zones are used to find one of the data sectors corresponding to a block address received from a host.

[0022] In the embodiment of FIGS. 2A and 2B, the disk drive comprises a plurality of heads (22₀-22₃) actuated over respective disk surfaces (16₀-16₃). The heads (22₀-22₃) are attached to the distal ends of actuator arms (24A-24C) which are rotated about a pivot by a voice coil motor (VCM) 26 in order to position the heads (22₀-22₃) over the disk surfaces (16₀-16₃). Each disk surface (16₀-16₃) comprises a number of servo sectors (28₀-28_N) that store coarse head position information (e.g., a track address) used to position the head over a target data track during a seek operation, and fine head position information (e.g., servo bursts) used to maintain the head over the target data track during read/write operations. The control circuitry 20 processes the servo sectors (28₀-28_N) to generate a VCM control signal 30 applied to the VCM 26 in a closed loop servo system.

[0023] FIG. 2C shows a flow diagram executed by the control circuitry 20 for finding a data sector corresponding to a block address received from a host using the logical zones. At step 32 an access command is received from a host including a block address associated with a read/write command. At step 34 the logical zone corresponding to the block address is located, at step 36 the head corresponding to the block address is located, and at step 38 the data track corresponding to the block address is located. At step 40 the control circuitry 20 executes the disk access command at the target data sector within the target data track.

[0024] Any suitable control circuitry 20 may be employed in the embodiments of the present invention. In one embodiment, the control circuitry 20 comprises a microprocessor executing instructions, the instructions being operable to cause the microprocessor to perform the steps of FIG. 2C as well as other functions 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 system on a chip (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 20 comprises suitable logic circuitry, such as state machine circuitry.

[0025] FIG. 4 shows an example format for the disk surfaces (16₀-16₃) according to an embodiment of the present invention. In this example, each disk surface corresponding to heads 22₀-22₃ comprises three physical zones PZ₁-PZ₃ having physical zone boundaries at predetermined radial locations. The physical zone PZ₁ on disk surface 16₀ has a physical zone boundary (right boundary) at a first predetermined radial location, wherein the first predetermined radial location is different from any of the radial locations of the physical zone boundaries on disk surface 16₁. The physical zone PZ₁ on the disk surface 16₁ has a physical zone boundary (right boundary) at a second predetermined radial location, wherein the second predetermined radial location is different from any of the radial locations of the physical zone boundaries on disk surface 16₀. The logical zone boundaries of logical zones LZ₁-LZ₆ are defined relative to the physical zone boundaries in that a new logical zone boundary occurs whenever there is a change in any one of the physical zones on any disk surface. Accordingly, in this embodiment the number of logical zones is greater than the number of physical zones for at least one of the disk surfaces (six logical zones and three physical zones in the example of FIG. 4). Preferably, these logical zones are defined for at least two of the disk surfaces, and in one embodiment, one set of logical zones defines the logical zone boundaries for the entire drive.

[0026] In one embodiment, the data sectors of one of the physical zones on a first disk surface (e.g., PZ₁ on disk surface 16₀) store data at a first data rate, and the data sectors of a corresponding physical zone on a second disk surface (e.g., PZ₁ on disk surface 16₁) store data at a second data rate different than the first data rate. Corresponding means PZ₁ on disk surface 16₀ corresponds to PZ₁ on disk surface 16₁ regardless of their vertical alignment. In yet another embodiment, the data tracks on a first disk surface (e.g., disk surface 16₀) comprise a first radial density, and the data tracks on a second disk surface (e.g., disk surface 16₁) comprise a second radial density different than the first radial density.

[0027] In still another embodiment, each disk surface comprises a plurality of servo tracks, and on at least one of the disk surfaces the radial density of the data tracks is different than the radial density of the servo tracks. This embodiment is illustrated in FIG. 3 which shows the format of servo tracks (ST) relative to the format of data tracks (DT). In this example, there are 256 quantized steps between the centerline of each servo track, and 303 quantized steps between the centerline of each data track. Therefore, the ratio of the radial density of servo tracks to data tracks is 256/303. Any suitable ratio of servo track density to data track density may be employed in the embodiments of the present invention.

[0028] In one embodiment, the control circuitry 20 is further operable to identify a plurality of clusters, wherein each cluster comprises a first number of servo tracks and a second number of data tracks, and the first number of servo tracks is different than the second number of data tracks. This embodiment is also illustrated in FIG. 3, wherein in this example each cluster comprises 4 full servo tracks ST₀-ST₃ (4×256=1024 steps) and 3 full data tracks DT₀-DT₂ (with a remainder of 115 steps as shown). In this embodiment, each cluster comprises an integer number of servo track spacings and a fractional number of data track spacings. Also in this embodiment, the data tracks are formatted such that the spacing of data tracks always begins relative to the start of a new cluster. In the example of FIG. 3, the spacing between the last data track (data track DT₂) of a current cluster and the first data track (data track DT₀) of the next cluster includes the remainder (303+115=418 steps). In an alternative embodiment, the remainder is distributed across the data tracks in any suitable manner so that the spacing between data tracks is substantially even.

[0029] Any suitable radial density may be selected for the data tracks in step increments, with the minimum distance between data tracks being the distance between servo tracks (256 steps). This allows the data track density (tracks per inch) as well as the linear density (bits per inch) to be optimized for each head/surface, while enabling a convenient mapping of host block addresses to target data sectors.

[0030] In one embodiment, the block address received from the host is a logical block address (LBA) that the control circuitry 20 maps to an absolute block address (ABA) corresponding to a target data sector. This LBA to ABA mapping facilitates the “mapping out” of defective data sectors to spare data sectors. Any suitable LBA to ABA mapping algorithm may be employed in the embodiments of the present invention.

[0031] In one embodiment, the ABA numbering follows a suitable serpentine pattern across the disk surfaces. This is illustrated in the embodiment of FIG. 4, wherein the serpentine pattern follows the width of a cluster along a current surface of a disk in one direction (e.g., OD to ID), and then follows along a cluster width of a next disk surface in the opposite direction (e.g., ID to OD). When the end of the cluster on the last disk surface is reached, the serpentine pattern continues starting with the next cluster on the first disk surface as illustrated in FIG. 4.

[0032] Note that because the physical zones do not change within a logical zone, the sectors per cluster cylinder (SPCC) are the same within each logical zone, wherein the SPCC is the number of sectors on all of the disk surfaces within the cluster cylinder. This is true even though the data track density and the linear bit density may be different across the disk surfaces. This constraint enables the convenient mapping of an ABA to a target data sector, which is understood with reference to the flow diagram of FIG. 5:

• • [0033] Step 42: Receive access command from host—An access command is received from a host, including a logical block address.
  • [0034] Step 44: Map LBA to ABA—The LBA received from the host is mapped to an ABA using any suitable algorithm.
  • [0035] Step 46: Find the logical zone corresponding to the ABA—Each logical zone has an associated starting ABA (S_ABA), which is computed as the SPCC times the number of clusters within each preceding zone. The logical zone corresponding to any given ABA is found by comparing the starting ABA of each logical zone to the target ABA.
  • [0036] Step 48: Find the cluster within the logical zone corresponding to the ABA—The cluster within the target logical zone is then found by comparing the target ABA to the SPCC for each cluster. For example, the control circuitry may be operable to subtract the starting ABA of the target logical zone from the target ABA to find the remainder, and then subtract the SPCC from the remainder repetitively until the result is less than the SPCC. The fractional SPCC is then used to find the target head/surface in the next step.
  • [0037] Step 50: Find the head within the cluster corresponding to the ABA—Once the cluster within the logical zone is found, the head/surface storing the target data sector is found by comparing the fractional SPCC to the sectors per cluster (SPC) for each disk surface starting with the first disk surface 16₀. For example, the control circuitry may be operable to subtract the SPC for each disk surface from the fractional SPCC found in the previous step until the result is less than the SPC. The remainder of this step is then used to find the target data track in the next step.
  • [0038] Step 52: Find the data track corresponding to the head and ABA—The target data track is then found by comparing the remainder of the previous step to the sectors per track (SPT) within the cluster on the target disk surface. For example, subtract the sectors per track from the remainder of the previous step until the result is less than the SPT.
  • [0039] Step 54: Find the servo track and a radial offset—Once the target data track is known, the corresponding servo track can be determined using the ratio of servo track density to data track density. The centerline of the target data track is typically located at a radial offset (in steps) from the target servo track. In one embodiment, the target servo track and radial offset are always determined relative to the left side of the cluster regardless as to the serpentine direction.

[0040] A better understanding of how an ABA is mapped to a target data sector is understood by considering two examples in FIG. 4, assuming the following format parameters:
SPCC₁=412=>S_ABA LZ₂=1236
SPCC₂=466=>S_ABA LZ₃=2168
SPC within cluster C₂ of LZ₂ on disk surface 16₀=124
SPC within cluster C₂ of LZ₂ on disk surface 16₁=105
SPC within cluster C₂ of LZ₂ on disk surface 16₂=90
SPC within cluster C₂ of LZ₂ on disk surface 16₃=147
SPT within cluster C₂ of LZ₂ on disk surface 16₁=35
SPT within cluster C₂ of LZ₂ on disk surface 16₂=30

[0041] In a first example illustrated in FIG. 6A, a target data sector (reference number 56 in FIG. 4) is found for ABA number 1897. The target logical zone (LZ₂) is found by comparing the S_ABA of the logical zones to the target ABA of 1897. A remainder is found by subtracting the S_ABA of the target logical zone (S_ABA LZ₂=1236) from the ABA number 1897 leaving a remainder of 661. The target cluster within LZ₂ is then found by subtracting the SPCC₂ from the remainder of 661 (which happens once in this case before the result is less than SPCC₂). The remainder (661−466=195) is then used to find the target head/surface by subtracting the SPC for each disk surface (which happens once in this case before the result is less than the SPC). The remainder (195−124=71) represents the sector number within cluster C₂ of LZ₂ on disk surface 16₁. The corresponding target data track and target data sector are then found by subtracting the sectors per track (SPT) within cluster C₂ of LZ₂ on disk surface 16₁ (71−35−35=1). Therefore, the target data sector is the second data sector of the third data track (data track DT₂ counting from right to left in FIG. 6A) within cluster C₂ of LZ₂ on disk surface 16₁. The corresponding servo track and radial offset is then found using the ratio of servo track density to data track density (256/303):
Target servo track=((4×256)−(2×303))/256=1 remainder 162.
In the above equation, the number of steps in two data track spacings (2×303) is subtracted from the total number of steps in the cluster (4×256) since the direction of the serpentine pattern is right to left for disk surface 16₁. Therefore, the target servo track is the second servo track (servo track ST₁ counting from left to right in FIG. 6A) within cluster C₂ of LZ₂ on disk surface 16₁, and the radial offset from the second servo track is 162 steps as shown in FIG. 6A.

[0042] In a second example illustrated in FIG. 6B, the target data sector (reference number 58 in FIG. 4) is found for ABA number 1967. The target logical zone (LZ₂) is found by comparing the S_ABA of the logical zones to the target ABA of 1967. A remainder is found by subtracting the S_ABA of the target logical zone (S_ABA LZ₂=1236) from the ABA number 1967 leaving a remainder of 731. The target cluster within LZ₂ is then found by subtracting the SPCC₂ from the remainder of 731 (which happens once in this case before the result is less than SPCC₂). The remainder (731−466=265) is then used to find the target head/surface by subtracting the SPC for each disk surface (which happens twice in this case before the result is less than the SPC). The remainder (265−124−105=36) represents the sector number within cluster C₂ of LZ₂ on disk surface 16₂. The corresponding target data track and target data sector are then found by subtracting the sectors per track (SPT) within cluster C₂ of LZ₂ on disk surface 16₂ (36−30=6). Therefore, the target data sector is the 7th data sector of the second data track (data track DT₁ counting from left to right in FIG. 6B) within cluster C₂ of LZ₂ on disk surface 16₂. The corresponding servo track and radial offset is then found using the ratio of servo track density to data track density (256/303):
Target servo track=(1×303)/256=1 remainder 47.
Therefore, the target servo track is the second servo track (servo track ST₁ counting from left to right in FIG. 6B) within cluster C₂ of LZ₂ on disk surface 16₂, and the radial offset from the second servo track is 47 steps as shown in FIG. 6B.

[0043] In one embodiment, the parameters needed to map a given ABA to a target data sector are stored in a table. For example, the starting ABA for each logical zone, the SPCC for each logical zone, the SPC within each logical zone on each disk surface, and the SPT for each cluster on each disk surface are stored in a table, wherein the appropriate table values are retrieved at each step in the above mapping process.