Abstract:
A computer hard disk drive has a drive controller that monitors the condition of the head-disk interface within the drive. In response to sensing a degradation of the head-disk interface, the drive prolongs the onset of failure by selectively altering performance parameters. In one embodiment, the internal pressure of the drive is increased to allow the air bearing surfaces of the heads to achieve a greater flying height above the surfaces of their respective disks, thereby delaying the onset of a catastrophic head-disk interface failure. In other embodiments, the spindle rotation rate and/or the slider head access rate are decreased to avoid hastening the imminent failure. Measurements of the condition and stability of the head-disk interface inside the drives are made by monitoring data error rates, head flying height, or other performance variables.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]    This is a divisional application of U.S. patent application Ser. No. 09/487,912, filed Jan. 19, 2000, entitled “SYSTEM AND METHOD FOR GRACEFULLY RELINQUISHING A COMPUTER HARD DISK DRIVE FROM IMMINENT CATASTROPHIC FAILURE”, which is herein incorporated by reference. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    This invention relates in general to an improved computer hard disk drive and in particular to avoiding catastrophic failure in a disk drive as long as possible. Still more particularly, the invention relates to a system and method for gracefully relinquishing a disk drive that is on the brink of catastrophic failure in order to transfer data from the failing drive to another storage medium.  
         BACKGROUND OF THE INVENTION  
         [0003]    Generally, a digital data access and storage system consists of one or more storage devices that store data on storage media such as magnetic or optical data storage disks. In magnetic disk storage systems, a storage device is called a hard disk drive (HDD), which includes one or more hard disks and an HDD controller to manage local operations concerning the disks. Hard disks are rigid platters, typically made of aluminum alloy or a mixture of glass and ceramic, covered with a magnetic coating. Typically, two or three platters are stacked vertically on a common spindle that is turned by a disk drive motor at several thousand revolutions per minute (rpm).  
           [0004]    The only other moving part within a typical HDD is the head assembly. Within most drives, one read/write head is associated with each side of each platter and flies just above or below the platter&#39;s surface. Each read/write head is connected to a semi-rigid arm apparatus which supports the entire head flying unit. More than one of such arms may be utilized together to form a single armature unit.  
           [0005]    Each read/write head scans the hard disk platter surface during a “read” or “write” operation. The head/arm assembly is moved utilizing an actuator which is often a voice coil motor (VCM). The stator of a VCM is mounted to a base plate or casting on which is also mounted the spindle supporting the disks. The base casting is in turn mounted to a frame via a compliant suspension. When current is fed to the motor, the VCM develops force or torque which is substantially proportional to the applied current. The arm acceleration is therefore substantially proportional to the magnitude of the current. As the read/write head nears the desired track, a reverse polarity signal is applied to the actuator, causing the signal to act as a brake, and ideally causing the read/write head to stop directly over the desired track.  
           [0006]    In rare circumstances, a disk drive will have a catastrophic failure wherein the data saved on the disk will be permanently lost and incapable of being retrieved. Unfortunately, prior art disk drives are incapable of delaying the onset of catastrophic failure in order to simultaneously transfer data from the failing drive to another known good drive or other storage medium.  
           [0007]    Accordingly, it is an object of the invention to provide an improved computer hard disk drive.  
           [0008]    It is an additional object of the invention to avoid catastrophic failure in a disk drive as long as possible.  
           [0009]    Still another object of the invention is to provide a system and method for gracefully relinquishing a disk drive that is on the brink of catastrophic failure in order to transfer data from the failing drive to another storage medium.  
           [0010]    The foregoing and other objects and advantages of the present invention will be apparent to those skilled in the art, in view of the following detailed description of the preferred embodiment of the present invention, taken in conjunction with the appended claims and the accompanying drawings.  
         SUMMARY OF THE INVENTION  
         [0011]    A computer hard disk drive has a drive controller that monitors the condition of the head-disk interface within the drive. The drive normally operates under ambient or relatively low internal pressure. However, when the drive is in imminent risk for a head-disk interface failure, the drive is pressurized to allow the air bearing surfaces of the heads to achieve a greater flying height above the surfaces of their respective disks, thereby delaying the onset of a catastrophic head-disk interface failure. In addition, the spindle rotation rate and/or the slider head access rate are decreased to avoid hastening the imminent failure. Measurements of the condition and stability of the head-disk interface inside the drives are made by monitoring data error rates, head flying height, and other performance variables.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0012]    So that the manner in which the features, advantages and objects of the invention, as well as others which will become apparent, are attained and can be understood in more detail, more particular description of the invention briefly summarized above may be had by reference to the embodiment thereof which is illustrated in the appended drawings, which drawings form a part of this specification. It is to be noted, however, that the drawings illustrate only a preferred embodiment of the invention and is therefore not to be considered limiting of its scope as the invention may admit to other equally effective embodiments.  
         [0013]    [0013]FIG. 1 is a schematic drawing of a computer hard disk drive constructed in accordance with the invention.  
         [0014]    [0014]FIG. 2 is a simplified block diagram of the drive of FIG. 1.  
         [0015]    [0015]FIG. 3 is a high level, logic flowchart of an illustrative embodiment of the method and system of the present invention utilized by the drive of FIG. 1. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0016]    Referring to FIG. 1, a schematic drawing of an information storage system comprising a magnetic hard disk file or drive  11  for a computer system is shown. Optimally, drive  11  is included in an array configuration of two or more drives. Drive  11  has an outer housing or base  13  containing a plurality of stacked, parallel magnetic disks  15  (one shown) which are closely spaced apart. Disks  15  are rotated by a motor located therebelow about a central drive hub  17 . A plurality of stacked, parallel actuator arms  21  (one shown) are pivotally mounted to base  13  about a pivot assembly  23 . A controller  19  is mounted to the base for selectively moving arms  21  relative to disks  15 .  
         [0017]    In the embodiment shown, each arm  21  comprises a mounting support  25 , a pair of parallel, cantilevered load beams or suspensions  27  extending from each mounting support  25 , and a head slider assembly  29  having at least one magnetic read/write head secured to each suspension  27  for magnetically reading data from or magnetically writing data to disks  15 . Suspensions  27  have a spring-like quality which biases or maintains them in parallel relationship relative to one another. A motor assembly  31  having a conventional voice coil motor is also mounted to pivot assembly  23  opposite head slider assemblies  29 . Movement of an actuator driver  33  (indicated by arrow  35 ) moves head slider assemblies  29  radially across tracks on the disks  15  until the heads on assemblies  29  settle on the target tracks. The head slider assemblies  29  operate in a conventional manner and always move in unison with one another, unless drive  11  uses a split actuator (not shown) wherein the arms move independently of one another.  
         [0018]    Referring now to FIG. 2, a simplified block diagram of a single disk drive  11  with relinquishment features is shown. Drive controller  19  monitors the head-disk interface condition. Drive  11  is preferably sealed and normally operates in an atmosphere at ambient or relatively low internal pressure. However, when one or more disk drives  11  is determined to be at risk for a head crash or some other head-disk interface failure is imminent, the internal pressure of the troubled drive  11  is increased via pressure means  41  to increase the density of the air inside base  13  to allow the air bearing surfaces of the heads to achieve a greater flying height above the surfaces of their respective disks  15 . Pressure means  41  may comprise a number of different devices for selectively manipulating the atmosphere inside base  13  including a compressor, a vacuum pump, or a vessel of pressurized gas. Alternatively, if the interior of base  13  is evacuated at a pressure below that of the ambient atmosphere under normal operating conditions, a vent-type mechanism may be employed to selectively allow the ambient atmosphere to enter the base by ventilation, or similarly pressurized by using the pump, etc. After venting, base  13  may be further pressurized above ambient pressure by other means.  
         [0019]    An increased flying height delays the onset of a catastrophic head-disk interface failure. In one embodiment, controller  19  reduces the rotational speed of disks  15  via spindle motor  17  and their rotation rate in order to not accelerate failure. Moreover, the data channel  43  is instructed to increase error recovery attempts and/or other enhanced data recovery operations such as reducing the slider head access rate in order to delay failure. By reducing the access rate, the flying height loss during the seek process is lowered since the radial acceleration is reduced.  
         [0020]    Preferably, the change in pressure, spindle rotation rate, and slider head access rate are driven by the rate at which the head-disk interface is degrading as a function of time. Measurements of the condition and stability of the head-disk interface inside the drives can be made by monitoring data error rates, head flying height, the number and severity of thermal asperities, the number of slider-disk contacts, the amount of power required at precise operating conditions such as air bearing natural frequencies, etc. Thresholds that represent a degraded state are previously set. If a degradation in the condition is detected, controller  19  notifies the host controller  45  that action will be taken to extend the life of drive  11 . The decision to take these actions is based on periodic or continuous measurements of the condition of the head-disk interface.  
         [0021]    For example, the relinquishing process can be initiated if the head flying height is reduced by approximately 50% or more. The relinquishing process also may be initiated if the dynamic flying height of a head indicates unusual flying characteristics such as head-disk intermittent contact. Once one or more thresholds have been achieved, controller  19  signals the host controller  45  that drive  11  should begin the relinquishment process. Based on the amount of data on the affected drive(s), the current demand for the data on the affected drive(s), and to what extent the head-disk interface has degraded, the controller  19  takes the necessary action to delay any failure.  
         [0022]    Referring now to FIG. 3, there is illustrated one embodiment of a high level, logic flow diagram of a method for gracefully relinquishing a hard disk drive in accordance with the invention. The method begins as illustrated at block  101  and proceeds to block  103  where the error rate of each or any head is determined. Next, a determination is made as to whether the error rate of each head has significantly increased, as depicted at block  105 . If the error rate increase is significant, the process proceeds to block  107  which will be explained below. If the error rate increase (if any) is insignificant, the change in flying height of the heads is computed, as illustrated at block  109 . Next, a determination is made as to whether the change in flying height (if any) is significant. If so, the process again proceeds to block  107 . If the change in flying height is insignificant, the process computes the number and severity of the thermal asperities by head, as depicted at block  113 .  
         [0023]    As illustrated at block  115 , another determination is made as to whether the increase (if any) in the number and severity of thermal asperities is significant. If so, the process proceeds to block  107 ; if not, the process computes the number of slider-disk contacts by head, as depicted at block  117 . Yet another determination is made as to whether the number of slider-head contacts has increased significantly (see block  119 ). If so, the process proceeds to block  107 ; if not, the process computes the amount of flying height modulation power present at air bearing, suspension, and arm natural frequencies for each head, as illustrated at block  121 . An additional determination is made as to whether the increase (if any) in power is significant (depicted at block  123 ). If the power increase is significant, the process proceeds to block  107 ; if not, the process terminates since no relinquishment will be required.  
         [0024]    Thus, both flying height modulation and radial track misregistration can be monitored. Flying height modulation can be monitored and the power at specific known air bearing, suspension, and arm frequencies can be compared to baseline values that are computed when the disk drive was manufactured. Similarly, radial track misregistration can be monitored by using the actuator servo system. The power at known frequencies that are likely to be excited when a head is in contact with a disk surface is compared to baseline values (where no contact was present). Measuring flying height modulation by using the readback signal amplitude modulation is well known in the art, as is monitoring track misregistration using the servo.  
         [0025]    At block  107 , the process first makes a determination as to whether the pressure in the base is at the maximum allowable (illustrated at block  127 ). If the pressure is not maximized, the internal drive pressure is increased, as depicted at block  129 . Once the pressure is maximized, the process proceeds to block  131  wherein a determination is made as to whether the spindle rotational speed is minimized. If the spindle rotational speed may be further reduced, it is performed as illustrated at block  133 . Once the rotational speed of the spindle is minimized, another determination is made as to whether the lowest flying slider still has adequate clearance relative to its associated disk, as depicted at block  135 . If so, the process returns to block  131 ; if not, the process proceeds to block  137  wherein a determination is made as to whether the seek rate is minimized. If the seek rate is not minimized, it is performed as illustrated at block  139 . Once the seek rate is minimized, the process proceeds to block  141  wherein the error retry attempts are increased. If this final exercise is futile the process terminates at block  125 .  
         [0026]    The invention has several advantages. The present process and apparatus described herein prolong the onset of catastrophic failure in a computer hard disk drive as long as possible. The delay allows at least some of the critical data that is saved on the failing disk to be transferred to a known good drive or an alternate storage medium before it is permanently lost and cannot be retrieved. The present invention uses all available means to delay the failure of the drive, including increasing flying height of the heads, reducing the spindle rotation and/or slider head access rates, and instructing the data channel to increase error recovery attempts or other enhanced data recovery operations.  
         [0027]    While the invention has been shown or described in only some of its forms, it should be apparent to those skilled in the art that it is not so limited, but is susceptible to various changes without departing from the scope of the invention.