Patent Publication Number: US-6657805-B2

Title: Method of controlling read write operation of a magnetic disk apparatus

Description:
This is a continuation of application Ser No. 09/225,972 filed Jan. 5, 1999 now U.S. Pat. No. 6,310,741. 
    
    
     BACKGROUND OF THE INVENTION 
     In a magnetic disk apparatus, when an amount of an offtrack of a magnetic head from the target track in the radial direction exceeds a predetermined value during data recording, there is the possibility that a part of the data of the neighboring track is erased and the information of the neighboring track cannot be read. 
     In a conventional magnetic disk apparatus using an embedded servo system including a data recording area and servo information for a recording track on a magnetic disk medium, a track position signal is demodulated from reproduced servo information during data writing and writing in the state of offtrack is prevented by monitoring the amount of offtrack during writing. Namely, an art for prohibiting the write operation is used when the amount of offtrack of the magnetic head in the direction of track width immediately before writing or during writing is more than a preset value. 
     SUMMARY OF THE INVENTION 
     The present invention relates to a magnetic disk apparatus for positioning a magnetic head for a recording track provided on a circular magnetic disk medium and recording information on it. 
     When the servo quality is high and the sampling cycle is very short, the aforementioned art is effective as an offtrack writing prevention means. However, in a magnetic disk apparatus using the embedded system having no dedicated servo surface and having servo information on the data surface, the location for storing servo signals is limited so as to reserve as many data recording areas as possible and as a result, it is hard to shorten the sampling cycle. Also with respect to a servo signal recorded on a magnetic disk medium, due to effects of vibration during writing of the servo signal, a medium defect, noise, and others, the quality thereof is not always sufficiently high and it is hard to make the specified value for monitoring a write position error sufficiently smaller. 
     With respect to the reliability of written data, when tracks A, B, and C are lined up side by side, the track A is shifted toward the track B and already written, and the track B is shifted toward the track C and already written, and if, when the track C is to be written, it is shifted toward the track B and written, the state of reproducing the data of the track B is a most severe condition. Therefore, to maintain the reliability, even in a case of combination of the aforementioned worst position errors, it is necessary to reserve the recorded data and it is a condition that the occurrence frequency is very low on a probability basis, so that it is requested to set the specified value for monitoring a position error to a more smaller value. 
     However, when the specified value for monitoring a position error is set to an extremely small value, write suspension (write fault) occurs frequently and there is the possibility that the equipment performance lowers and a malfunction of write inhibit is caused. 
     On the other hand, in correspondence with an increase in the recording capacity requested to a magnetic disk apparatus at present and to realize a decrease in cost, it is essential to improve the recording density and it is necessary to narrow the track pitch equivalent to the density in the radial direction on a magnetic disk medium. On a magnetic disk whose track pitch is minimized, the condition for positioning the magnetic head in the direction of track width becomes severe more and more. 
     The present invention is realized in consideration of such a problem of the prior art and an object of the present invention is to provide a magnetic disk apparatus for making the offtrack of the recording track smaller without sacrifice of the access speed and improving the reliability by reducing the occurrence probability of write fault at the same time. 
     According to the present invention, the above object is accomplished by detecting a position error of the magnetic head in the direction of track width on a magnetic disk medium by a plurality of threshold values, typically two threshold values and when it is decided that a position error which may cause a failure depending on the state of position error when data is written on the neighboring track, though it is not fatal, is caused (write warning), by writing the data as it is on the track causing offtrack, temporarily write-inhibiting the track neighboring to the track, reading the information written on the track causing the offtrack later when the equipment is in the state of idle, and rewriting the information on another track. 
     Namely, the magnetic disk apparatus of the present invention comprises a magnetic disk medium having tracks arranged concentrically or spirally, a magnetic head for recording or reproducing for the tracks, a detection means for detecting position information of the magnetic head in the direction of track width during recording, a decision means for deciding the magnitude of a position error of the magnetic head in the direction of track width using the position information and a plurality of threshold values, and a means for limiting the later recording position according to the decision result by the decision means. 
     The limitation of recording position according to the decision result by the decision means is to temporarily inhibit writing data, for example, when it is decided by the decision means at the time of recording data on a preset track that the amount of offtrack is larger than a preset threshold value, on the whole or a part of one track on both sides neighboring to the track. 
     When it is decided by the decision means that the amount of offtrack when data is written on the preset track last is larger than the preset threshold value, the data of the track is rewritten on another track so as to maintain the data. 
     The magnetic disk apparatus of the present invention has a track information table for registering, when it is decided by the decision means that the amount of offtrack when data is written on the preset track last is larger than the preset threshold value, the track as a track requiring rewriting and temporarily registering the track neighboring to the track as a write inhibit track. 
     Furthermore, the magnetic disk apparatus has a logical-physical address conversion table for converting the logical address of a data write or read instruction from a host device to a physical address on the magnetic disk medium and a means for changing the logical-physical address conversion table at any time. 
     When it is decided by the decision means that the amount of offtrack when the data is rewritten on the rewritten track is smaller than the preset threshold value, that is, the rewriting succeeds and the data is completely recorded, the means for changing the logical-physical address conversion table at any time updates the logical-physical address conversion table and corresponds the physical address of the rewritten track to the logical address of the track requiring rewriting. 
     The aforementioned rewrite is executed when the write or read instruction from the host device is monitored, and the instruction is not issued, and the operation by an instruction from the host device is not necessary. 
     Typically, when the amount of position error PE meets the condition of Ewf&gt;PE&gt;=Eww for two threshold values Ewf and Eww meeting Ewf&gt;Eww, the decision means registers the track in the track information table as a track requiring rewrite and temporarily write-inhibits the tracks on both sides neighboring to the track. 
     Or, when the amount of position error PE meets the condition of Ewf&gt;PE&gt;=Eww for two threshold values Ewf and Eww meeting Ewf&gt;Eww, the decision means registers the track in the track information table as a track requiring rewrite and temporarily write-inhibits the track neighboring to the track in the direction of position error. However, in this case, it is necessary to know not only the magnitude of the amount of position error PE but also the direction of the position error. 
     According to the magnetic disk apparatus of the present invention, when the threshold value for monitoring a position error is set in a plurality of stages, typically 2 stages and the rewrite process by write warning is executed, it is possible to make the offtrack of the recording track smaller without sacrifice of the access speed. By doing this, the threshold value of write fault can be increased, and the occurrence probability of write fault reduces, and the reliability improves. At the same time, since the occurrence probability of write fault reduces, the frequency of retry reduces and the access speed during write improves. Furthermore, since the offtrack of the recording track becomes smaller, the error rate during read improves and the reliability and access speed improve. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram showing an example of the constitution of a magnetic disk apparatus of the present invention. 
     FIG. 2 is a drawing showing the constitution of tracks on a magnetic disk medium. 
     FIG. 3 is a flow chart for explaining the sequence of the data write process by a magnetic disk apparatus of the present invention. 
     FIG. 4 is a flow chart for explaining the sequence of the data rewrite process by a magnetic disk apparatus of the present invention. 
     FIGS. 5 a - 5   c  is a drawing for explaining the relationship of offtrack on a magnetic disk medium. 
    
    
     DETAILED DESCRIPTION 
     The embodiments of the present invention will be explained hereunder with reference to the accompanying drawings. 
     FIG. 1 is a block diagram showing an example of the constitution of a magnetic disk apparatus of the present invention. In FIG. 1, inside an HDA (head disk assembly)  1 , a plurality of magnetic disk media  3  rotating by a motor  4 , a plurality of magnetic heads  5  opposite to each of the magnetic disk media  3 , an actuator  6  for moving each magnetic head  5  in one, and a pre-amplifier  7  for writing and reading the magnetic heads are housed. 
     Outside the HDA  1 , a circuit board  2  is fixed. The output from the pre-amplifier  7  is inputted to a read data demodulating circuit  8 , demodulated to digital data, and then inputted to an interface controller unit  9 . The interface controller unit  9  is connected to a host computer via a connector and an interface cable. 
     The output from the pre-amplifier  7  is also inputted to a position signal reproducing circuit  10  and a position signal of the magnetic heads  5  demodulated by the position signal reproducing circuit  10  is inputted to an A/D converter  11 . The A/D converter  11  is connected to a microprocessor  12 . The microprocessor  12  fetches position information and performs the calculation for the seek or track follow-up operation. The microprocessor  12  performs the conversion process from logical address to physical address and the write inhibit track management as described later and a logical-physical address conversion table  17  and a track information table  16  for that purpose are connected to the microprocessor  12 . The microprocessor  12  may be replaced with a gate array, ASIC, or other logical means if each of them can realize the same function. 
     The output of the microprocessor  12  is converted to an analog signal by a D/A converter  13  and inputted to an actuator driver circuit  14 , which generates a drive current for the actuator  6  and controls positioning of the magnetic heads  5 . 
     During data write, data is sent to a data write circuit  15  from the interface controller unit  9  and performs the write operation for the magnetic heads  5  via the write circuit in the pre-amplifier  7 . 
     FIG. 2 shows a schematic view of the constitution of tracks on a magnetic disk medium. On each track, a servo area and a data area are alternately arranged and several tens servo areas are arranged on one track (one round). A position signal is reproduced in each servo area and position information and physical track No. information are obtained. 
     The microprocessor  12  generally performs following control for following up tracks. When the host computer issues a write command, the microprocessor starts the interface process for decoding the command. In this case, the microprocessor converts the write logical address from the host computer using the logical-physical address conversion table  17  and decides a physical write address (track, sector, etc.). When movement to the track to be written is necessary, the microprocessor  12  starts the seek control. 
     After the seek control or seek process is finished, the microprocessor  12  returns to the following control or following process again and when the positioning to the target track of the magnetic head  5  is sufficiently stabilized, a command complete signal for notifying the end of seek control becomes active. After the command complete signal becomes active, the microprocessor reads ID information and starts the data write operation when the discriminated information is correct. 
     When large data extending a plurality of sectors is to be written, in a servo area between data areas, a servo signal is demodulated and subjected to following control and in a data area, data is written again. In this case, from the demodulation result of the servo signal, the amount of position error of the magnetic head from the track center is monitored. 
     Conventionally, when the amount of position error is more than a predetermined specified value, it is decided as a write fault, and the write operation is stopped, and writing is attempted for the same track again, and when a write fault occurs several times, it is decided as a write error. 
     FIG. 3 shows a flow chart of the write process of this equipment. When a data write instruction is issued from the host computer, the microprocessor  12  examines the recording enable area on the disk  3  using the logical-physical address conversion table  17  and the track information table  16 , decides the recording track (Step  11 ), and moves the magnetic head  5  to the desired track (Step  12 ). After seek completion, the microprocessor reads the servo data and performs the following operation (Step  13 ). 
     In this example, the allowable threshold value of position error (PE) is divided into 2 stages (Ewf, Eww (Ewf&gt;Eww)) and the position error is monitored. In detection of position error at Step  14 , PE&gt;Ewf is decided, and in the case of YES, Write Fault (WF) is decided on the assumption that there is the possibility that the position error results in a fatal failure, and the write fault process is performed (Step  15 ). When NO is decided in detection of position error at Step  14 , in detection of position error at Step  16 , PE&gt;Eww is decided, and in the case of NO, it is decided that the position error is sufficiently small, and the program goes to Step  18 , and the data is written as it is. When YES is decided in detection at Step  16 , it is decided that the position error is comparatively larger on the corresponding track and there is the possibility that it results in a failure depending on the state of position error when data is written on the neighboring track, though it is not fatal (write warning: WW), and the corresponding track is registered in the track information table  16  as write warning WW (Step  17 ), and thereafter, the program goes to Step  18 , and the data is written on the corresponding track as it is. The tracks on both sides neighboring to the track registered in the track information table  16  as write warning WW are temporarily write-inhibited. 
     At Step  19 , it is decided whether data write is finished, and when it is finished, the program goes to Step  20 , and the writing is finished, and the equipment enters the state of idle. When it is decided in detection at Step  19  that data to be written remains, it is decided at Step  21  whether a data write enable area remains on the track, and when it remains, the program returns to Step  13 , and by detecting a position error of the magnetic head, data is also written on the track. 
     When recording a large amount of continuous data extending a plurality of tracks, data is written according to the aforementioned sequence and after writing on one track (track N) is finished, the program goes to Step  22  from Step  21 . When the track is decided as write warning WW in detection at Step  16  prior to it, the writing on the neighboring two tracks is inhibited, so that the process at Step  22  unconditionally skips the neighboring tracks, examines an empty track, goes to Step  12 , seeks the track, and writes the continued data. When the decision at Step  16  is NO, the process at Step  22  examines a data write enable track without skipping the neighboring tracks, goes to Step  12 , seeks the selected track, and writes data on it (when the neighboring tracks are write enabled, the continued data is written on the neighboring tracks). 
     When this process is repeated and the recording of a series of data is finished, the writing is finished, and the program goes to Step  20  from Step  19 , and the equipment enters the state of idle. In the state of idle at Step  20 , when the write/read command from the host computer is stopped and a fixed time elapses, the program is automatically moved to the rewriting process. 
     FIG. 4 shows a flow chart of the rewriting process. The rewriting process is a process of re-recording data of a track among tracks written until immediately before which is decided as write warning WW and saved on the track information table  16  on an empty track. When a fixed time elapses in the state of idle, the microprocessor  12  examines whether there is a track registered as write warning WW in the track information table  16  (Step  31 ), and when no track is registered, the equipment enters the state of idle again and obeys an instruction from the host computer (Step  34 ). 
     When a track registered as write warning WW exists in the track information table in detection at Step  31 , the program goes to Step  32  and the track information table  16  is read. Next, the program goes to Step  33  and checks whether there is an instruction from the host computer and when there is an instruction, the rewriting is stopped and the equipment obeys an instruction from the host computer (Step  34 ). When there is no instruction, the data on the track registered in the track information table as write warning WW is read (Step  35 ), and the magnetic head is moved to the write enable track (Step  36 ), and the corresponding data is written. 
     In this case, the servo data is read (Step  37 ), and in the same way as with the normal write process explained in FIG. 3, a position error in 2 stages is decided (Steps  38 ,  40 ), and when it is decided as write fault WF, the write fault process is performed (Step  39 ), and when it is decided as write warning WW, the corresponding track is registered in the track information table  16  as write warning WW (Step  41 ), and then data is written (Step  42 ). 
     When the data write on the corresponding track is finished, the program returns to Step  31  from Step  44 , and whether write warning WW is registered in the track information table is checked again, and the same process is repeated. With respect to a track succeeding in rewriting, the logical-physical address conversion table is updated (Step  43 ) and the physical track succeeding in rewriting corresponds to the logical address of the corresponding data. Whether there is an instruction from the host computer is confirmed every rewriting on one track and an instruction from the host computer is executed on a priority basis. When rewriting of all the tracks registered in the write warning WW table is finished, the rewrite process is finished and the equipment is moved to the state of idle. 
     On a track (complete track) which is not decided as write fault WF or write warning WW, data is written in the state of sufficiently small position error. Therefore, the threshold value of write fault decision when data is to be written on the neighboring tracks of the complete track can be made larger compared with the case of monitoring of position error in 2 stages. 
     Setting of a threshold value of write fault decision will be explained by referring to FIG.  5 . FIG.  5 ( a ) is a drawing showing an ideal state of no position error. FIG.  5 ( b ) is a drawing showing an arrangement under the worst condition of position error in the conventional system. E0× indicates the amount of worst offtrack when the threshold value of write fault decision in the conventional system is set to E0. Recorded tracks  70  and  71  are recorded by shifting in the direction of approaching a recording track  72  by E0×. The recording track  72  is also written by shifting toward the recorded track  71  by E0× and a part is overwritten on the recorded track  71 . In this case, if it is attempted to reproduce the track  71 , a part of the track  71  is overwritten on the track  72 , and a reproduced signal is small, and moreover a part of recording signals of the neighboring tracks  70  and  72  is read as a noise. Therefore, in consideration of both the amount of worst offtrack of the neighboring tracks already recorded and the amount of worst offtrack of the track being recorded at present, the threshold value E0 of position error of write fault is set. 
     FIG.  5 ( c ) is a drawing showing an arrangement of tracks under the worst condition in the system of the present invention. In monitoring of position error in two stages, the threshold values Ewf and Eww in two stages are set so as to meet the relationship of Ewf&gt;E0&gt;Eww. When the neighboring track  76  already recorded is a complete track, the amount of worst offtrack is Ewwx smaller than E0×. Therefore, even if the amount of offtrack of the track  77  being recorded at present is E0×, which is larger than the one in the case of monitoring, the possibility that the data of the neighboring track  76  recorded is destroyed is low. 
     In this example, the neighboring two tracks of a track decided as write warning WW are write-inhibited and when a large amount of continuous data extending a plurality of tracks is to be recorded, the recorded two tracks  75  and  76  neighboring to the recording track  77  are always complete tracks and have the relationship shown in FIG.  5 ( c ). 
     Namely, even if a failure occurs on the complete track  76  that a part thereof is erased due to offtrack of the neighboring track  77 , it is only an effect from one side and the offtrack of the self track is small, so that the effect is smaller than that of the conventional method. 
     When the threshold value Ewf which becomes a write fault increases, the probability that it becomes a write fault naturally reduces and the reliability improves. The position error of recorded data during reading is small, so that the error rate improves. At the same time, the probability of performing the retry operation due to a position error during write/read reduces and as a result, the access speed improves. 
     The threshold value Eww of write warning is smaller than the specified value E0 of write fault in the conventional system (E0&gt;Eww) and the occurrence probability is high. However, even if write warning WW occurs, there is no need to suspend the write process and the rewrite process is performed by use of the time of the state of idle that there is no instruction from the host computer, so that there are few disadvantages in the access speed. 
     In the above embodiment, an example that one track neighboring to the inner periphery of a track on which write warning WW occurs and one track neighboring to the outer periphery are temporarily write-inhibited and the recorded contents of the track on which write warning WW occurs are rewritten on another track later is explained. However, it is possible to fetch information on the direction of position error in the detection of position error at Step  16  shown in FIG.  3  and write-inhibit only one track neighboring in the shifted direction. 
     In this embodiment, the write position is controlled in track units including a plurality of sectors. However, it is possible to change the control unit to the sector unit and execute write inhibit and address conversion in sector units. 
     In a magnetic disk apparatus in which tracks are spirally arranged, a disk cannot be physically delimited in track units. In this case, by distinguishing sectors equivalent to about one round as one track and performing the same control so as to prevent the neighboring one of a track or sector of write warning from writing, the present invention can be executed.