Magnetic head control capable of avoidance media bumps during seeking process

According to one embodiment, a magnetic disk drive selects in command evaluation in reordering processing, a command accessible in a shortest time. The device determines whether media bumps which influence a dynamic flying height (DFH) control exist in a seek section between completion of a previous command and start of a selected command or not, calculates a latency necessary for avoidance of the media bumps if it is determined by the determination that the media bumps which influence the DFH control exist, and selects the command accessible in the shortest time including the time obtained by summing the latency calculated by the calculation as the command to be next processed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from Japanese Patent Application. No. 2017-179026, filed Sep. 19, 2017, the entire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to magnetic disk drive and a magnetic head control method.

BACKGROUND

In a magnetic disk drive, in general, dynamic flying height (DFH) control of raising a magnetic head to a flying height position for seek simultaneously with seek start and falling the magnetic head to a flying height position for read/write (hereinafter R/W) before seek completion is executed.

In the magnetic disk drive, control for media bump avoidance is executed together with DFH control. In this case, media bumps exist in the seek destination direction of the seek start track and, if the magnetic heads are expected to collide with the media bumps, control of delaying the seek start until the magnetic heads reaches the flying height position for seek is executed. In addition, media bumps exist in the seek source direction of the seek completion track and, if the magnetic heads are expected to collide with the media bumps, control of falling the magnetic heads after passing the media bumps is executed.

If the above-explained DFH control and control for media bump avoidance are executed, a latency caused by the media bump avoidance control is not considered, but the time obtained by summing a seek time determined from a seek distance and a rotational latency determined by a relationship between an R/W enable sector position and sector position of a command to be evaluated, after seek completion, is used and, if a command accessible in the shortest time is selected by the reordering, the seek is delayed due to the media bump avoidance, rotational latency occurs in a case where the seek is not completed before a start sector of a selected command, and the performance is degraded.

The object to be solved by the embodiments is to provide a magnetic disk drive and a magnetic head control method capable of reducing the rotational latency by considering the seek latency which occurs due to the media bump avoidance control executed together with the DFH control, at the reordering operation.

DETAILED DESCRIPTION

In general, according to one embodiment, a magnetic disk drive includes a determiner, a calculator and a selector. The determiner determines whether media bumps which influence a dynamic flying height (DFH) control exist in a seek section between completion of a previous command and start of a selected command or not in a reordering operation. The calculator calculates latency necessary for avoidance of the media bumps if it is determined by the determiner that the media bumps which influence the DFH control exist. The selector selects the command accessible in the shortest time including the time obtained by summing the latency as the command to be next processed.

Embodiments

A structure of a magnetic disk drive (hard disk drive: HDD) according to the embodiments will be explained with reference toFIG. 1toFIG. 4.FIG. 1is a block diagram schematically showing a magnetic disk drive (HDD) according to the embodiments. An HDD10shown inFIG. 1comprises a housing11, a magnetic disk12serving as a recording medium arranged in the housing11, a spindle motor14supporting and rotating the magnetic disk12, and a plurality of magnetic heads16which write data to the magnetic disk12and read data from the magnetic disk12. The HDD10comprises a head actuator18which moves and positions each of the magnetic heads16onto an arbitrary track on the magnetic disk12. The head actuator18comprises a suspension assembly which supports the magnetic heads16to be movable and a voice coil motor (VCM) which rotates the suspension assembly, though not illustrated in the drawing.

The HDD10comprises a head amplifier30, a main controller40, and a drive controller48. The head amplifier30is provided on, for example, the suspension assembly of the head actuator18and is electrically connected to the magnetic heads16. The main controller40and the drive controller48are constituted on, for example, a control circuit board (not shown) provided on a back surface side of the housing11. The main controller40comprises an operation processor (central processing unit: CPU)401, a read only memory (ROM)402for storing programs, a random access memory403for data processing work, a read/write (R/W) controller404, a data buffer controller405, a data buffer unit406, and a host interface (IF) controller407, and is connected to the elements via a bus408. The main controller40is electrically connected to the head amplifier IC30and the driver IC48to the VCM22and the spindle motor14. In addition, the main controller40can be connected to a host computer (RAID controller)20under control of the host interface (IF) controller407.

Control of the main controller40on the HDD10having the above-explained configuration will be explained with reference toFIG. 2toFIG. 4.FIG. 2is a cross-sectional view for explanation flying height of the magnetic head under general DFH control, at a seek operation,FIG. 3is a cross-sectional view for explanation flying height of the magnetic head under general DFH control with a media bump avoidance, at a seek operation, andFIG. 4is a diagram showing an example of media bump information preliminarily measured for each medium. InFIG. 2andFIG. 3, Tx represents the time, Hx represents the head flying height, Sx/Fx represents the location (track), Dx represents the defect area edge (track), and Bx represents the media bump location.

The main controller40forms and holds information on media bumps in The form of media bump information shown inFIG. 4, in the RAM403. As shown inFIG. 2, when executing seek from read/write end location S1to read/write start location S2, the main controller40executes dynamic flying height (DFH) control that changes the flying height of the magnet head16from the previous read/write (or the standby) flying height H1to flying height Hs for seek, and change the flying height Hs to flying height H2for read/write before read/write.

In the embodiments, the time to change the flying height of the magnetic heads16from H1to Hs is T1, the time to change the head flying height of the magnetic heads16from Hs to H2is T2, and the time elapsed until the evaluated command start is T1+Ts+T2as shown inFIG. 2. The main controller40determines whether the media bumps exist in a seek section in which the flying height is not the flying height Hs for seek in the seek section or not, by using the media bump information.

FIG. 3shows a DFH control example in which seek of the same section as that shown inFIG. 2is executed if media bumps exist in the seek section in the HDD10according to the embodiments. If media bump B1exists in a section in which the flying height of the magnetic heads16is changed from H1shown inFIG. 3to Hs, the HDD10according to the embodiments raises the magnetic heads16from H1shown inFIG. 3to Hs and then executes seek to pass the media bump BP1.

The time to raise the magnetic heads16from H1shown inFIG. 3to Hs is the time obtained by summing the time to raise the magnetic heads16from H1shown inFIG. 3to H1wwithout seeking at S1inFIG. 3and the time to raise the magnetic heads16from H1wshown inFIG. 3to Hs while seeking from S1shown inFIG. 1to F1′, and the time matches T1shown inFIG. 2. A section from S1shown inFIG. 3to F1′ of the seek section in which the magnetic heads16are raised is set to be long in the figure but seek may not be executed until the magnetic heads16are made to fly at S1shown inFIG. 3.

In the HDD10according to the embodiments, if media bump B2exists in a section in which the flying height of the magnetic heads16is changed from Hs shown inFIG. 3to H2, the flying height of the magnetic heads16is changed from Hs shown inFIG. 3to H2after the magnetic heads16pass the media bump BP2. In the embodiments, the time to lower the fly of the magnetic heads16from Hs shown inFIG. 3to H2is the time obtained by summing the time to fall the magnetic heads16from. Hs shown inFIG. 3to H2wwhile seeking from F2′ to S1inFIG. 3and the time to fall the magnetic heads16from H2wshown inFIG. 3to H2without seeking at S1inFIG. 3, and the time matches T2shown inFIG. 2.

In the embodiments, change of the flying height is started while seeking from F2′ inFIG. 3to S2, but the flying height may be changed after reaching S2inFIG. 3.

In the embodiments, the time T1wto raise the magnetic heads16from H1shown inFIG. 3to H1wwithout seeking at S1inFIG. 3can be calculated by subtracting the time necessary to seek the section between S1shown inFIG. 3and B1sfrom the time to raise the magnetic heads16from H1shown inFIG. 3to Hs.

The time T2wto fail the magnetic heads16having reached S2inFIG. 3from H2wshown inFIG. 3to H2can be calculated by subtracting the time necessary to seek from B2eto S2from the time to fall the magnetic heads16from Hs shown inFIG. 3to H2.

The above-explained processing of calculating T1wand T2wis determined by a positional relationship between the seek start point and end point and the media bumps, and each of T1wand T2w, the time in which the fly control is executed without seeking becomes a seek latency generated by the media bumps.

As a method of calculating the times T1sand T2sto control flying height while seeking as values other than 0 after simplifying the processing of calculating T1wand T2w, increasing the time to enable the control of flying height while seeking, and reducing the latency T1wand the latency T2woccurring by the media bumps, the time T1sshown inFIG. 3can be calculated as the seek start operation time in which the seek is controlled to start from D1sand pass at B1sand the time T2scan be calculated as the seek stop operation time in which the seek is controlled to pass at B2eand stop at D2e, by adding defect (defect information) which cannot be accessed by the computer20shown inFIG. 1to the surroundings of the media bumps BP1and BP2representing inFIG. 3the distance from S1shown inFIG. 3to F1′ and the distance from F2′ to S2.

Reordering operation select a command which should be next executed while executing a certain command, in the HDD10executing the DFH control of the embodiments, will be explained with reference toFIG. 5toFIG. 8.FIG. 5is a top view showing a seek locus image of the magnetic heads under the DFH control for explanation of a reordering operation,FIG. 6is a top view showing a seek locus image of the magnetic heads under the DFH control with a media bump avoidance for explanation of a reordering operation,FIG. 7is a flowchart for explanation of a processing reordering operation, andFIG. 8is a characteristic graph showing a relationship between the number of media bumps and the random access performance (A is a graph in the conventional device and B is a graph in the embodiments).

In the above reordering operation, the time is calculated and evaluated in accordance with the flowchart shown inFIG. 7. S1inFIG. 3is a currently running command R/W completion position, and S2inFIG. 3is an R/W start position of a command to be evaluated.

InFIG. 7, if the reordering is started (step S11), a pure seek time (Ta=T1s+Ts+T2s) is calculated from a relationship between the R/W end position of the currently running command (seek start sector inFIG. 6) and the R/W start position of the evaluated command (target sector inFIG. 5) (step S12). If no media bumps exist on a medium surface of the magnetic heads16of the seek source, it is determined whether the media bumps exist in a section from S1to F1′ for seek at time T1at which the head flying height is raised to the flying height for seek or not, with reference to the media bump information shown inFIG. 4. More specifically, it is determined whether the number of media bumps existing on the medium surface of the magnetic heads16of the seek source is larger than or equal to constant number a (number of media bumps—performance characteristic inFIG. 8) or not (step S13) and, if the number of media bumps is larger than or equal to the constant number a, the presence of the media bumps in the section from S1to F1′ is determined (step S14), and the time obtained by adding T1wto the pure seek time as the flying height control time is handled as a real seek time (step S15). If the number of media bumps is smaller than the constant number a, it is determined that no media bumps exist without executing the search (step S16) and the pure seek time is handled as the real seek time (step S17), to suppress increase in the calculation time.

The random access performance (input/output operations per second: IOPS) shown inFIG. 8is an index indicating the number of time of executing the 10 per second.

Next, it is determined whether the number of media bumps existing on the medium surface of the magnetic heads16of the seek source is larger than or equal to constant number b (i.e., the number of media bumps at which the performance is reversed by (the number of media bumps—performance characteristic inFIG. 8)) or not (step S18) and, if the number of media bumps is larger than or equal to the constant number b, the presence of the media bumps in the section from F2′ to S2is determined with reference to the media bump information (step S19), and the time obtained by adding T2wto the calculated real seek time as the flying height control time is handled as the real seek time (step S20). If the number of media bumps is smaller than the constant number b, it is determined that no media bumps exist without executing the search (step S21) and the calculated real seek time is handled as the real seek time (step S22), to suppress increase in the calculation time.

A sector (R/W ready sector inFIG. 6) in which read/write is enabled is obtained from the real seek time calculation result (step S23), a rotational latency is calculated based on a positional relationship between an R/W enable sector and the R/W start position (i.e., the target sector inFIG. 5) of the evaluated command (step S24), and the time necessary for processing evaluation is handled as the real seek time+rotational latency (step S25). Presence of the other evaluated commands is determined. (step S26) and, if the other evaluated commands exist the processing is executed by changing the evaluated commands from step S12, and if no other evaluated commands exist a sequence of processing is ended.

In the processing, T1wand T2winFIG. 3may be values different at read and write. In addition, in the processing, the processing of determining whether the media bumps exist when using T1wand T2wmay not be executed at an access at which T1wand T2winFIG. 3become 0. In the processing, the times T1sand T2sinFIG. 3may be included in T1wand T2w. In the processing, if it can be determined whether the media bumps can exist from the seek distance from S1inFIG. 3to S2inFIG. 3, whether the media bumps exist or not may be determined from the seek distance alone.

In the magnetic disk drive according to the embodiments, as explained above, when access to the disk is being executed together with the command processing, in the reordering, the command which should be next processed is determined in the command group standing by inside the HDD, the time obtained by summing the seek time determined in accordance with the seek distance and the rotational latency which is determined after the seek completion by the positional relationship between the R/W enable sector position and the sector of the evaluated command is used in the command evaluation of the reordering, if the command accessible in the shortest time is selected it is determined whether the media bumps influencing the DFH control exist in the seek section from the previous command completion to the evaluated command start or not, if the media bumps influencing the DFH control are determined to exist the command accessible in the shortest time can be selected at the time obtained by summing the latency necessary for the media bump avoidance.

In other words, by detecting the media bumps influencing the DFH/seek control in the seek section and executing the reordering while considering the latency which occurs due to the media bump avoidance, the seek time from the current command completion position to the next command candidate lead position can be calculated correctly, the optimum next command can be thereby selected, and the degradation of performance caused by the media hump avoidance control can be suppressed.

In addition, by changing consideration of the media bumps in accordance with the number of media bumps, the latency occurring by the media bump avoidance control can be calculated in the HDD having a smaller number of media bumps, a maximum number of commands that can be evaluated by the reordering executed between the commands can be reduced, and degradation of the performance can be suppressed.

By changing consideration of the media bumps in accordance with the seek distance, in a case where the seek control and the DFH control system are different in accordance with the seek distance, influence to the media bump avoidance control can be calculated correctly, and degradation of the performance can be suppressed.

By separately calculating the latency occurring due to the media bump avoidance control for read and write, in a case where the DFH control systems are different for read and write, influence to the media bump avoidance control can be calculated correctly, and degradation of the performance can be suppressed.

By separately calculating the latency occurring due to the media bump avoidance control for the respective magnetic heads in consideration of the characteristic (DFH control speed) for each of the magnetic heads, in a case where the DFH control speeds are different for each of the magnetic heads, influence to the media bump avoidance control can be calculated correctly, and degradation of the performance can be suppressed.

By inserting the defect (defect information) for the predetermined track skip into the surroundings of the media bumps and reducing areas subjected to the media bump avoidance control, the calculation occurrence frequency and the calculation time considering the media bump avoidance control at the reordering can be reduced, and degradation of the performance can be suppressed.