Abstract:
A control method of controlling a disk storage unit, includes: obtaining, by a computer, for a plurality of sectors allocated on a disk included in the disk storage unit, track identifying information that identifies a track to which sectors belong, in a first order starting from a first start sector; and storing, if first track identifying information obtained in a first sector of the plurality of sectors does not match second track identifying information obtained in a second sector of the plurality of sectors immediately before the first sector, a data length from the first start sector to the second sector in a storage unit.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2012-150243, filed on Jul. 4, 2012, the entire contents of which are incorporated herein by reference. 
     FIELD 
     The embodiments discussed herein are related to a control method of controlling a disk storage unit and a system. 
     BACKGROUND 
     A magnetic disk storage unit is a storage unit that stores data to be processed by an information processing apparatus. The magnetic disk storage unit has one or a plurality of platters that store data. One platter has areas divided in ring shapes. Each area divided in a ring shape on the platter is referred to as a track. The track is further divided into units called sectors where data is recorded. The length of data that is able to be stored in one sector is fixed. 
     A related technology is disclosed in Japanese Laid-open Patent Publication No. 8-272540. 
     SUMMARY 
     According to one aspect of the embodiments, a control method of controlling a disk storage unit, includes: obtaining, by a computer, for a plurality of sectors allocated on a disk included in the disk storage unit, track identifying information that identifies a track to which sectors belong, in a first order starting from a first start sector; and storing, if first track identifying information obtained in a first sector of the plurality of sectors does not match second track identifying information obtained in a second sector of the plurality of sectors immediately before the first sector, a data length from the first start sector to the second sector in a storage unit. 
     The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, as claimed. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  illustrates an example of a system; 
         FIG. 2  illustrates a functional structure of a controller; 
         FIG. 3  illustrates an example of calculating a data length of the outermost track on a platter; 
         FIG. 4  illustrates an example of a procedure for calculating a data length of the outermost track; 
         FIGS. 5A and 5B  each illustrate an example of a magnetic disk storage unit; 
         FIG. 6  illustrates an example of calculating a data length of the innermost track on a platter; 
         FIG. 7  illustrates an example of a procedure for calculating a data length of the innermost track; 
         FIG. 8  illustrates an example of a procedure for calculating data lengths of tracks; 
         FIG. 9  illustrates an example of calculating a data length of the outermost track; 
         FIG. 10  illustrates an example of a procedure for calculating a data length of the outermost track; 
         FIG. 11  illustrates an example of calculating a data length of the innermost track on a platter; 
         FIG. 12  illustrates an example of a procedure for calculating a data length of the innermost track; 
         FIG. 13  indicates an example of an expression to calculate the number of zones; 
         FIG. 14  illustrates an example of information stored in a zone information storage unit; 
         FIG. 15  indicates an expression to calculate a ratio of a data area; 
         FIG. 16  illustrates an example of information stored in a zone information storage unit; 
         FIG. 17  illustrates an example of a hardware structure; 
         FIG. 18  illustrates an example of a magnetic disk storage unit; 
         FIG. 19  illustrates an example of a magnetic disk storage unit; 
         FIG. 20  illustrates an example of a magnetic disk storage unit; and 
         FIG. 21  illustrates an example of a magnetic disk storage unit. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     In a recording method for a magnetic disk storage unit, the total number of sectors in a track on the outer circumference side of a disk is larger than that in a track on the inner circumference side to increase a storage capacity. Accordingly, when a platter is rotated one turn, a larger amount of data is read from and written to an outer track on the platter when compared with an inner track on the platter. A speed at which data is read from and written to the platter becomes faster toward the outer circumference of the platter. A speed at which data is read from and written to the outermost track is fastest, and a speed at which data is read from and written to the innermost track is slowest. 
     For example, when data is read from or written to a magnetic disk storage unit, even if data has the same data length, a time taken to read or write the data may vary depending on the accessed track. Accordingly, when, for example, data is stored in a plurality of magnetic disk storage units in a distributed manner, read and write performance may be lowered. 
       FIG. 1  illustrates an example of a system. The system  1  in  FIG. 1  includes a controller  100 , magnetic disk storage units  105  and  106 , and an information processing apparatus  107 . 
     The controller  100  includes a central processing unit (CPU)  101 , a memory  102 , a storage unit adapter  103 , and an information processing apparatus adapter  104 , all of which are mutually coupled through a bus. 
     The CPU  101  executes calculation processing or other processing that is executed by the controller  100 . The memory  102  stores information to be used in the calculation processing executed by the CPU  101 . Programs to be executed by the CPU  101  may be loaded in the memory  102 . 
     The controller  100  is coupled through the storage unit adapter  103  to the magnetic disk storage units  105  and  106 , and is coupled through the information processing apparatus adapter  104  to the information processing apparatus  107  that uses a storage unit. The storage unit adapter  103  is coupled to the magnetic disk storage units  105  and  106  by using, for example, a Small Computer System Interface (SCSI). Although, in  FIG. 1 , the magnetic disk storage units  105  and  106  are coupled to the controller  100 , any number of magnetic disk storage units may be coupled to the controller  100 . 
     The magnetic disk storage units  105  and  106  may be magnetic disk storage units that are able to perform data communication by the SCSI standard. The length of data that is able to be stored in one sector is 520 bytes (512-byte storage area and 8-byte redundant area). 
     The information processing apparatus adapter  104  may be coupled to the information processing apparatus  107  through, for example, a fiber channel or a storage area network (SAN). 
     The information processing apparatus  107  may be, for example, a server apparatus or personal computer (PC) that processes data stored in the magnetic disk storage unit  105  or  106 . 
       FIG. 2  illustrates a functional structure of a controller. The controller  100  includes a converter  201 , a number comparing unit  202 , a track data length calculating unit  203 , a zone count determining unit  204 , a block data length determining unit  205 , a data area calculating unit  206 , a division commanding unit  207 , and a storage unit  208 . The storage unit  208  includes a number information storage unit  209 , a track information storage unit  210 , and a zone information storage unit  211 . 
     The converter  201  issues a physical address converting command to a logical block address (LBA). The LBA acquires the head number and track number of an assigned sector. The physical address converting command is a command with which the LBA assigned to a sector identifies the head number and track number of the sector. The magnetic disk storage units  105  and  106  may be storage units that perform processing as commanded by a physical address converting command and send a processing result to the controller  100 . 
     The number comparing unit  202  determines whether there is a match between the head number and track number stored in the number information storage unit  209  and the head number and track number obtained by the converter  201 . The number comparing unit  202  stores the head number and track number in the number information storage unit  209  if desired. 
     The track data length calculating unit  203  calculates the data length of a track on the platter included in the magnetic disk storage units  105  and  106 , based on information about the head number and track number of a sector, the information being stored in the storage unit  208 . The track data length calculating unit  203  stores the calculated data length of the track in the track information storage unit  210 . 
     The zone count determining unit  204  determines the number of zones by using the data length of the track, which has been calculated by the track data length calculating unit  203 , and assigns zone numbers to the zones, the zone numbers being used to identify the zones. The zone count determining unit  204  stores the assigned zone numbers in the zone information storage unit  211  if desired. 
     The block data length determining unit  205  determines the data length of a block in each zone determined by the zone count determining unit  204  by using the data length of the track, which has been calculated by the track data length calculating unit  203 . The block data length determining unit  205  stores in the storage unit  208  the determined data length of the block and the number of the zone that includes the block having the data length in relation to each other. 
     The data area calculating unit  206  calculates a ratio of a data area occupied by each zone to the entire data area in the corresponding magnetic disk storage unit  105  or  106  by using the number of zones and the zone number determined by the zone count determining unit  204 . The data area calculating unit  206  stores the calculated data area ratio of each zone in the storage unit  208 . 
     The division commanding unit  207  divides the data area in the magnetic disk storage units  105  and  106  coupled to the controller  100 , based on the information stored in the storage unit  208 . The converter  201 , number comparing unit  202 , track data length calculating unit  203 , zone count determining unit  204 , block data length determining unit  205 , data area calculating unit  206 , and division commanding unit  207 , which are illustrated in  FIG. 2 , may function when, for example, the CPU  101  included in the controller  100  in  FIG. 1  executes programs stored in the memory  102 . 
     The storage unit  208  stores information created or to be referenced by the functional units. The storage unit  208  includes the number information storage unit  209 , track information storage unit  210 , and zone information storage unit  211 . 
     The number information storage unit  209  stores a sector obtained by the converter  201  and the head number and track number of the sector in relation to each other. 
     The track information storage unit  210  stores the data length of the track, which has been calculated by the track data length calculating unit  203 . 
     The zone information storage unit  211  stores the number of zones determined by the zone count determining unit  204 . The zone information storage unit  211  stores the zone numbers determined by the zone count determining unit  204 , the data length per block in each zone, which has been determined by the block data length determining unit  205 , and the ratio of the data area in each zone to the entire data area in the corresponding magnetic disk storage unit  105  or  106  determined by the data area calculating unit  206 , in relation to one another. 
     The storage unit  208  may be, for example, the memory  102  included in the controller  100  illustrated in  FIG. 1 . The head number is a number assigned to a magnetic head included in the magnetic disk storage unit so that the magnetic head to be used to read data from or write data to the platter is identified. The magnetic disk storage unit  105  or  106  has platters, on both surfaces of which data is able to be stored. One magnetic head is provided for one recoding surface of a platter. For examples, sectors in which data is read and written by using heads with different head numbers belong to different recording surfaces of platters. 
     The track number is a number assigned to a track so that the track on the platter is identified. For example, sectors having different track numbers belong to different tracks. Although the head number and track number are information in a numeric form, the numbers may be in non-numeric form if they are identifiers at are able to identify a head and a track. 
       FIG. 3  illustrates an example of calculating a data length of the outermost track on a platter.  FIG. 4  illustrates an example of a procedure for calculating the data length of the outermost track. 
     The converter  201  obtains the head number and track number of a sector having an LBA of 0x0000 (smallest LBA) (S 401 ). The sector having the LBA 0x0000 may be described as the first sector. In  FIG. 3 , the first sector  301  is illustrated as the first sector having the LBA 0x0000. In the magnetic disk storage units  105  and  106 , the first sector  301  having the LBA 0x0000 may be in the outermost track. When the converter  201  issues a physical address converting command to the first sector  301 , a head number of 0x00 and a track number of 0x00 assigned to the first sector  301  are obtained as illustrated in  FIG. 3 . 
     After the head number and track number of the first sector  301  have been obtained, the converter  201  stores the obtained head number and track number of the first sector  301  in the number information storage unit  209  (S 402 ). 
     The converter  201  obtains the head number and track number of a sector having an LBA that is one larger than the LBA of the current sector (S 403 ). For example, when the converter  201  issues a physical address converting command to a sector  302 , illustrated in  FIG. 3 , having an LBA of 0x0001, its head number and track number are obtained. 
     After the head number and track number of sector  302  have been obtained, the number comparing unit  202  compares the head number of the first sector  301  and the head number of sector  302 . The number comparing unit  202  compares the track number of the first sector  301  and the track number of sector  302 . The number comparing unit  202  determines whether, in the first sector  301  and sector  302 , there is a match between the head numbers and between the track numbers (S 404 ). If the number comparing unit  202  determines that the head number and track number of sector  302  match the head number and track number of the first sector  301 , the processing returns to operation S 403 . The converter  201  executes operation S 403 , after which the converter  201  executes operation S 404 . 
     The processing in operations S 403  and S 404  is repeated until the number comparing unit  202  detects in operation S 404  that the obtained head number or track number differs from the head number or track number stored in the number information storage unit  209 . For example, in  FIG. 3 , if sector  302  is taken as a sector to be compared by the number comparing unit  202 , after a determination made in operation S 404 , the processing in operations S 403  and S 404  is repeated because the head number and track number of sector  302  are the same as the head number and track number of the first sector  301 . 
     If the number comparing unit  202  determines in operation S 404  that the obtained head number or track number differs from the head number or track number stored in the number information storage unit  209 , the number comparing unit  202  sends a notification to the track data length calculating unit  203 . Upon receipt of the notification from the number comparing unit  202 , the track data length calculating unit  203  calculates the data length of sectors from the first sector  301  to the current sector, which is, for example, a sector having an LBA that is one smaller than the LBA of the sector in which a different head number or a different track number has been detected by the number comparing unit  202 . The track data length calculating unit  203  stores the calculated data length in the track information storage unit  210  as the data length of the outermost track (S 405 ). 
     If, for example, sector  304  is taken as a sector to be compared in operation S 404 , a head number of 0x01 assigned to sector  304  differs from a head number of 0x00, assigned to the first sector  301 , that is stored in the number information storage unit  209 . Therefore, operation S 405  is executed by the track data length calculating unit  203 ; the data length of sectors from the first sector  301  to sector  303  illustrated in  FIG. 3  is calculated. If the calculated data length is, for example, 512 kilobytes, the track data length calculating unit  203  stores, in the track information storage unit  210 , that the data length of the outermost track is 512 kilobytes. 
     The data length of the outermost track in the magnetic disk storage units  105  and  106  may be calculated by the procedure described above. 
       FIGS. 5A and 5B  illustrate an example of a magnetic disk storage unit. In  FIGS. 5A and 5B , the method of assigning LBAs differs.  FIG. 5A  illustrates a magnetic disk storage unit in which LBAs are assigned in the order of platters. In  FIG. 5A , the track data length calculating unit  203  calculates the data length of the outermost track when the number comparing unit  202  detects a different head number as illustrated in  FIG. 3 .  FIG. 5B  illustrates a magnetic disk storage unit in which LBAs are assigned in the order of tracks on the same platter. In  FIG. 5B , the track data length calculating unit  203  calculates the data length of the outermost track when the number comparing unit  202  detects a different track number. 
       FIG. 6  illustrates an example of calculating the data length of the innermost track on a platter.  FIG. 7  illustrates an example of a procedure for calculating the data length of the innermost track. 
     The converter  201  obtains the head number and track number of a sector having the maximum LBA in terms of the capacity of the magnetic disk storage unit (S 701 ). The sector having the maximum LBA in terms of the capacity of the magnetic disk storage unit may be described as the last sector. In  FIG. 6 , the last sector  601  is illustrated as the last sector having an LBA of 0xFF80. In the magnetic disk storage units  105  and  106 , the last sector  601  is in the innermost track. For example, the converter  201  issues a physical address converting command to the last sector  601  illustrated in  FIG. 6  to obtain a head number of 0x07 and a track number of 0xFF assigned to the last sector  601 . 
     After having obtained the head number and track number of the last sector  601 , the converter  201  stores the obtained head number and track number of the last sector  601  in the number information storage unit  209  (S 702 ). 
     The converter  201  obtains the head number and track number of a sector having an LBA that is one smaller than the current LBA (S 703 ). For example, after executing operations S 701  and S 702 , the converter  201  issues a physical address converting command to sector  602  with an LBA of 0xFF7F, which is one smaller than the LBA of the last sector  601  to obtain its head number and track number. 
     After having obtained the head number and track number of sector  602 , the number comparing unit  202  compares the head number of sector  602  with the head number of the last sector  601  that is stored in the number information storage unit  209 . The number comparing unit  202  compares the track number of sector  602  with the track number of the last sector  601  that is stored in the number information storage unit  209 . The number comparing unit  202  determines, based on the comparison results, whether the last sector  601  and sector  602  have the same head number and the same track number (S 704 ). If the number comparing unit  202  determines that the last sector  601  and sector  602  have the same head number and the same track number, the converter  201  execute operation S 703  again, after which the number comparing unit  202  executes operation S 704 . 
     After that, operations S 703  and S 704  are repeated until the number comparing unit  202  detects in operation S 704  that the obtained head number or track number differs from the head number or track number stored in the number information storage unit  209 . For example, in  FIG. 6 , if sector  602  is taken as a sector to be compared by the number comparing unit  202 , after a determination has been made in operation S 704 , operations S 703  and S 704  are repeated because the head number and track number of sector  602  are the same as the head number and track number of the last sector  601 . 
     If the number comparing unit  202  determines in operation S 704  that the obtained head number or track number differs from the head number or track number stored in the number information storage unit  209 , the number comparing unit  202  sends a notification to the track data length calculating unit  203 . Upon receipt of the notification from the number comparing unit  202 , the track data length calculating unit  203  stores the head number and track number of the current sector, which is, for example, the sector in which a different head number or a different track number has been detected by the number comparing unit  202 , in the number information storage unit  209  (S 705 ). 
     If, for example, sector  603  is taken as a sector to be compared by the number comparing unit  202 , a head number of 0x06 assigned to sector  603  differs from a head number of 0x07, assigned to the last sector  601 , that is stored in the number information storage unit  209 . Therefore, the head number 0x06 and track number 0xFF of sector  603  are stored in the number information storage unit  209  in operation S 705  executed by the track data length calculating unit  203 . 
     After operation S 705  has been executed, the converter  201  obtains the head number and track number of a sector having an LBA that is one smaller than the current LBA (S 706 ). 
     The number comparing unit  202  compares the head number obtained by the converter  201  in operation S 706  with the head number of sector  603  that is stored in the number information storage unit  209 . The number comparing unit  202  compares the track number obtained by the converter  201  in operation S 706  with the track number of sector  603  that is stored in the number information storage unit  209 . The number comparing unit  202  determines, based on the comparison results, whether the head numbers are the same and the track numbers are the same (S 707 ). If the number comparing unit  202  determines that the head number and track number obtained by the converter  201  in operation S 706  respectively match the head number and track number of sector  603 , the processing returns to operation S 706 . The converter  201  executes operation S 706 , after which the number comparing unit  202  executes operation S 707 . 
     After that, operations S 706  and S 707  are repeated until the number comparing unit  202  detects in operation S 707  that the obtained head number or track number differs from the head number or track number stored in the number information storage unit  209 . For example, in  FIG. 6 , if sector  604  is taken as a sector to be compared by the number comparing unit  202 , after a determination made in operation S 707 , operations S 706  and S 707  are repeated because the head number and track number of sector  604  are the same as the head number and track number of the sector  603 . 
     If the number comparing unit  202  determines in operation S 707  that the obtained head number or track number differs from the head number or track number stored in the number information storage unit  209 , the number comparing unit  202  sends a notification to the track data length calculating unit  203 . Upon receipt of the notification from the number comparing unit  202 , the track data length calculating unit  203  calculates the data length of sectors from sector  603  to the current sector, which is, for example, a sector having an LBA that is one smaller than the LBA of the sector in which a different head number or a different track number has been detected by the number comparing unit  202 . The track data length calculating unit  203  stores the calculated data length in the track information storage unit  210  as the data length of the innermost track (S 708 ). 
     If, for example, sector  605  is taken as a sector to be compared in operation S 707 , a head number of 0x05 assigned to sector  605  differs from a head number of 0x06, assigned to sector  603 , that is stored in the number information storage unit  209 . Therefore, operation S 708  is executed by the track data length calculating unit  203 ; the data length of sectors from sectors  603  to  604  illustrated in  FIG. 6  is calculated. If the calculated data length is, for example, 256 kilobytes, the track data length calculating unit  203  stores, in the track information storage unit  210 , that the data length of the innermost track is 256 kilobytes. 
     The data length of the innermost track in the magnetic disk storage units  105  and  106  are calculated by the procedure described above. 
     The data length of the innermost track may be set to the data length of sectors from sector  603  to sector  604 . The magnetic disk storage unit may include a storage area that is not used by the user (user unused area), in which data is not rewritten by the user (the user is not permitted to rewrite data), in addition to a storage area in which data can be rewritten in response to a request from the user. The user unused area is allocated in, for example, a track near the innermost circumference of the platter in the magnetic disk storage unit. The user unused area is a storage area to be used to store configuration information about the magnetic disk storage unit or to be used for repair at the occurrence of a failure. Since the user unused area may not be allocated in an entire track, a track in the vicinity of the user unused area may include both a storage area in which data can be rewritten in response to a request from the user and the user unused area. When, for example, a user unused area is allocated in a track near the innermost circumference of the platter in the magnetic disk storage units  105  and  106 , a sector included in the user unused area may exist in the track including the last sector  601 . Accordingly, as illustrated in  FIG. 6 , the data length of sectors from sector  603  to sector  604  may be set as data length of the innermost track without setting the track including the last sector  601  as the innermost track. 
     Accordingly, possibility of the track including the user unused area being processed as the innermost track may be suppressed. The user unused area may be allocated in a track near the innermost circumference of the platter. If the user unused area is allocated in a track near the outermost circumference of the platter, the data length of the outermost track may be the data length of sectors from a sector in which a different head number has been first detected to a sector immediately before a sector in which a different head number has been detected next. 
     The data length of the outermost track is calculated in  FIG. 4 , and the data length of the innermost track is calculated in  FIG. 7 . When LBAs are assigned as illustrated in  FIG. 5B , the data length of a track other than the outermost track and innermost track may be calculated. 
       FIG. 8  illustrates an example of a procedure for calculating data lengths of tracks. In  FIG. 8 , the data length of each track between the outermost track and innermost track of a platter is calculated. 
     The controller  100  executes operations S 401  to S 405  illustrated in  FIG. 4  to calculate the data length of the outermost track (S 801 ). Operation S 801  may be substantially the same as or similar to operations S 401  to S 405  in  FIG. 4 . 
     The converter  201  obtains the head number and track number of a sector having an LBA that is one larger than the LBA of the current sector (S 802 ). For example, operation S 802  may be substantially the same as or similar to operation S 403  in  FIG. 4 . 
     After execution of operation S 802 , the number comparing unit  202  compares the track number obtained in operation S 802  with the track number stored in the number information storage unit  209 . The number comparing unit  202  determines, based on the comparison result, whether the track numbers are the same (S 803 ). If the number comparing unit  202  determines in operation S 803  that the track numbers are the same, the number comparing unit  202  executes operation S 805 . 
     If the number comparing unit  202  determines in operation S 803  that the track numbers are not the same, the number comparing unit  202  sends a notification to the track data length calculating unit  203 . Upon receipt of the notification from the number comparing unit  202 , the track data length calculating unit  203  calculates the data length of sectors from the sector taken when the numbers have been stored in the number information storage unit  209  to a sector having an LBA that is one smaller than the current LBA. The track data length calculating unit  203  stores the head number and track number of the current sector and stores the calculated data length as the data length of the outermost track in the track information storage unit  210  (S 804 ). After the track data length calculating unit  203  has executed operation S 804 , the number comparing unit  202  executes operation S 805 . 
     In operation S 805 , the number comparing unit  202  compares the head number obtained in operation S 802  with the head number stored in the number information storage unit  209 . The number comparing unit  202  determines, based on the comparison result, whether the head numbers are the same. If the number comparing unit  202  determines that the head numbers are the same, the number comparing unit  202  executes processing staring from operation S 802 . 
     If the number comparing unit  202  determines in operation S 805  that the track numbers are not the same, the number comparing unit  202  sends a notification to the track data length calculating unit  203 . Upon receipt of the notification from the number comparing unit  202 , the track data length calculating unit  203  determines that the track, the data length of which has been calculated at the last but one, is the innermost track, and determines the data length calculated at the last but one as the data length of the innermost track (S 806 ). 
     After the track data length calculating unit  203  has executed operation S 806 , the controller  100  terminates the track data length calculation processing illustrated in  FIG. 8 . 
     The data lengths of tracks are obtained sequentially from the outermost track by the procedure described above. When a head number is changed, for example, when a switchover of a recording surface of a platter is detected, the track data length calculation processing is terminated. In  FIG. 8 , when operation S 804  is first executed, the data length stored in the track information storage unit  210  by the track data length calculating unit  203  may be the data length of the outermost track. In operation S 806 , the data length stored in the track information storage unit  210  by the track data length calculating unit  203  may be the data length of the innermost track. 
       FIG. 9  illustrates an example of calculating the data length of the outermost track.  FIG. 10  illustrates an example of a procedure for calculating the data length of the outermost track. 
     The converter  201  obtains the head number and track number of a sector having an LBA of 0x0000 (S 1001 ). The sector having the LBA 0x0000 may be described as the first sector. In  FIG. 9 , the first sector  901  is illustrated as the first sector having the LBA 0x0000. In the magnetic disk storage units  105  and  106 , the first sector  901  having the LBA 0x0000 may be in the outermost track. When the converter  201  issues a physical address converting command to the first sector  901 , a head number of 0x00 and a track number of 0x00 assigned to the first sector  901  are obtained as illustrated in  FIG. 9 . 
     After the head number and track number of the first sector  901  have been obtained, the converter  201  stores the obtained head number and track number of the first sector  901  in the number information storage unit  209  (S 1002 ). 
     The converter  201  obtains the head number and track number of a sector having an LBA that is 0x80 (that is 128 in decimal or is equivalent to a data length of 64 kilobytes) larger than the LBA of the current sector (S 1003 ). The value of 0x80 may be appropriately changed. For example, when the converter  201  issues a physical address converting command to sector  902  having an LBA of 0x0080 illustrated in  FIG. 9 , the head number and track number are obtained. 
     After the head number and track number of sector  902  have been obtained, the number comparing unit  202  compares the head number of the first sector  901  and the head number of sector  902 . The number comparing unit  202  compares the track number of the first sector  901  and the track number of sector  902 . The number comparing unit  202  determines whether, in the first sector  901  and sector  302 , there is a match between the head numbers and between the track numbers (S 1004 ). If the number comparing unit  202  determines that the head number and track number of sector  902  match the head number and track number of the first sector  901 , the processing returns to operation S 1003 . The converter  201  executes the above processing, after which the converter  201  executes operation S 1004 . 
     After that, operations S 1003  and S 1004  are repeated until the number comparing unit  202  detects in operation S 1004  that the obtained head number or track number differs from the head number or track number stored in the number information storage unit  209 . For example, in  FIG. 9 , if sector  902  is taken as a sector to be compared by the number comparing unit  202 , after a determination made in operation S 1004 , operations S 1003  and S 1004  are repeated because the head number and track number of sector  902  are the same as the head number and track number of the first sector  901 . 
     If the number comparing unit  202  determines in operation S 1004  that the obtained head number or track number differs from the head number or track number stored in the number information storage unit  209 , the number comparing unit  202  sends a notification to the track data length calculating unit  203 . Upon receipt of the notification from the number comparing unit  202 , the track data length calculating unit  203  calculates the data length of sectors from the first sector  901  to the current sector, which is, for example, a sector having an LBA that is 0x80 smaller than the LBA of the sector in which a different head number or a different track number has been detected by the number comparing unit  202 . The track data length calculating unit  203  stores the calculated data length in the track information storage unit  210  as an approximate value of the data length of the outermost track (S 1005 ). 
     If, for example, sector  904  is taken as a sector to be compared in operation S 1004 , a head number of 0x01 assigned to sector  904  differs from a head number of 0x00, assigned to the first sector  901 , that is stored in the number information storage unit  209 . Therefore, operation S 1005  is executed by the track data length calculating unit  203 ; and the data length of sectors, illustrated in  FIG. 9 , from the first sector  901  to a sector having an LBA that is one smaller than the LBA of sector  903  is calculated. If the calculated data length is, for example, 512 kilobytes, the track data length calculating unit  203  stores, in the track information storage unit  210 , that an approximate value of the data length of the outermost track is 512 kilobytes. 
     An approximate value of the data length of the outermost track in the magnetic disk storage unit  105  or  106  is calculated by the procedure described above. 
     Since the head numbers and track numbers of sectors are obtained in 0x80 increments, an approximate value of the data length of a track may be obtained by a smaller amount of calculation or in a shorter calculation time. 
       FIG. 11  illustrates an example of calculating the data length of the innermost track on a platter.  FIG. 12  illustrates an example of a procedure for calculating the data length of the innermost track. 
     The converter  201  obtains the head number and track number of a sector having the maximum LBA in terms of the capacity of a magnetic disk storage unit (S 1201 ). The sector having the maximum LBA in terms of the capacity of the magnetic disk storage unit may be described as the last sector. In  FIG. 11 , the last sector  1101  is illustrated as the last sector having an LBA of 0xFF80. In the magnetic disk storage units  105  and  106 , the last sector  1101  may be in the innermost track. For example, the converter  201  issues a physical address converting command to the last sector  1101  illustrated in  FIG. 11  to obtain a head number of 0x07 and a track number of 0xFF assigned to the last sector  1101 . 
     After having obtained the head number and track number of the last sector  1101 , the converter  201  stores the obtained head number and track number of the last sector  1101  in the number information storage unit  209  (S 1202 ). 
     The converter  201  obtains the head number and track number of a sector having an LBA that is 0x80 smaller than the LBA of the current sector (S 1203 ). For example, the converter  201  issues a physical address converting command to sector  1102  with an LBA of 0xFF00 to obtain its head number and track number. 
     After having obtained the head number and track number of sector  1102 , the number comparing unit  202  compares the head number obtained in operation S 1203  with the head number stored in the number information storage unit  209 . The number comparing unit  202  compares the track number of sector  1102  that has been obtained in operation S 1203  with the track number of the last sector  1101  that is stored in the number information storage unit  209 . The number comparing unit  202  determines, based on the comparison results, whether there is a match between the track number of the last sector  1101  that is stored in the number information storage unit  209  and the track number of sector  1102  that has been obtained in operation S 1203  (S 1204 ). If the number comparing unit  202  determines that the track number of the last sector  1101  and the track number of sector  1102  are the same, the processing returns to operation S 1203 . The converter  201  executes operation S 1203 , after which the number comparing unit  202  executes operation S 1204 . 
     After that, operations S 1203  and S 1204  are repeated until the number comparing unit  202  detects in operation S 1204  that the obtained head number or track number differs from the head number or track number stored in the number information storage unit  209 . For example, in  FIG. 11 , if sector  1102  is taken as a sector to be compared by the number comparing unit  202 , after a determination made in operation S 1206 , operations S 1203  and S 1204  are repeated because the head number and track number of sector  1102  are the same as the head number and track number of the last sector  1101 . 
     If the number comparing unit  202  determines in operation S 1204  that the head number or track number obtained in operation S 1203  differs from the head number or track number stored in the number information storage unit  209 , the number comparing unit  202  sends a notification to the track data length calculating unit  203 . Upon receipt of the notification from the number comparing unit  202 , the track data length calculating unit  203  stores the head number and track number of the current sector, which is, for example, the sector in which a different head number or a different track number has been detected by the number comparing unit  202 , in the number information storage unit  209  (S 1205 ). 
     If, for example, sector  1103  is taken as a sector to be compared by the number comparing unit  202 , a head number of 0x06 assigned to sector  1103  differs from a head number of 0x07, assigned to the last sector  1101 , that is stored in the number information storage unit  209 . Therefore, the head number 0x06 and track number 0xFF of sector  1103  are stored in the number information storage unit  209  in operation S 1205  executed by the track data length calculating unit  203 . 
     After operation S 1205  has been executed, the converter  201  obtains the head number and track number of a sector having an LBA that is 0x80 smaller than the current LBA (S 1206 ). 
     The number comparing unit  202  compares the head number obtained by the converter  201  in operation S 1206  with the head number of sector  1103  that is stored in the number information storage unit  209 . The number comparing unit  202  compares the track number obtained by the converter  201  in operation S 1206  with the track number of sector  1103  that is stored in the number information storage unit  209 . The number comparing unit  202  determines, based on the comparison results, whether the head numbers are the same and the track numbers are the same (S 1207 ). If the number comparing unit  202  determines that the head number and track number obtained by the converter  201  in operation S 1206  respectively match the head number and track number of sector  1103 , the processing returns to operation S 1206 . Then, the converter  201  executes operation S 1206 , after which the number comparing unit  202  executes operation S 1207 . 
     After that, operations S 1206  and S 1207  are repeated until the number comparing unit  202  detects in operation S 1207  that the obtained head number or track number differs from the head number or track number stored in the number information storage unit  209 . For example, in  FIG. 11 , if sector  1104  is taken as a sector to be compared by the number comparing unit  202 , after a determination has been made in operation S 1207 , operations S 1206  and S 1207  are repeated because the head number and track number of sector  1104  are the same as the head number and track number of the sector  1103  that are stored in the number information storage unit  209 . 
     If the number comparing unit  202  determines in operation S 1207  that the obtained head number or track number differs from the head number or track number stored in the number information storage unit  209 , the number comparing unit  202  sends a notification to the track data length calculating unit  203 . Upon receipt of the notification from the number comparing unit  202 , the track data length calculating unit  203  calculates the data length of sectors from sector  1103  to the current sector, which is, for example, a sector having an LBA that is 0x80 larger than the LBA of the sector in which a different head number or a different track number has been detected by the number comparing unit  202  (in  FIG. 11 , the current sector is sector  1104 ). The track data length calculating unit  203  stores the calculated data length in the track information storage unit  210  as an approximate value of the data length of the innermost track (S 1208 ). 
     If, for example, sector  1105  is taken as a sector to be compared in operation S 1207 , a head number of 0x05 assigned to sector  1105  differs from a head number of 0x06, assigned to sector  1103 , that is stored in the number information storage unit  209 . Therefore, operation S 1208  is executed by the track data length calculating unit  203 ; and the data length of sectors, illustrated in  FIG. 11 , from sector  1103  to a sector having an LBA that is 0x80 larger than the LBA of sector  1105  is calculated. If the calculated data length is, for example, 256 kilobytes, the track data length calculating unit  203  stores, in the track information storage unit  210 , that an approximate value of the data length of the innermost track is 256 kilobytes. 
     An approximate value of the data length of the innermost track in the magnetic disk storage units  105  and  106  is calculated by the procedure described above. 
     Since the head numbers and track numbers of sectors are obtained in 0x80 increments, an approximate value of the data length of a track may be obtained by a smaller amount of calculation or in a shorter calculation time. 
     If the data length of a track on a platter included in a magnetic disk storage unit is unknown, the data length of the track or its approximate value may be calculated. 
     Although the converter  201  obtains the head numbers and track numbers of sectors in 0x80 increments, this increment may be appropriately changed according to the specifications of the storage unit. If, for example, the minimum value of the data length in data processing executed by the controller  100  is 64 kilobytes and the length of data storable in one sector is 512 bytes, the head numbers and track numbers of sectors may be obtained in 0x80 increments. Data processing executed by the controller  100  may be less affected, and the data lengths of tracks may be calculated more efficiently. After the data length of the outermost track and the data length of the innermost track have been calculated, the storage areas in the magnetic disk storage units  105  and  106  are divided. An approximate value of the data length of the track may be used, or the calculated data length of the track may be used. Alternatively, information that has been obtained in advance may be used. 
     A zone may be a group of a plurality of blocks. The data lengths of blocks belonging to the same zone are set to the same value. For example, in a zone on the outer side of a platter, as the data length of, for example, one track becomes longer, the data length of the block is set to a larger value. Since zones and the data lengths of blocks are set in this way, as the data length of the track becomes longer, the data length of the block is set to a larger value. Even if the data length of the block becomes long, the number of seeks performed by the magnetic head to scan sectors and a time taken for the seeks may be reduced. 
       FIG. 13  indicates an example of an expression to calculate the number of zones. The zone count determining unit  204  determines the number of zones into which the entire data area is to be divided according to the expression indicated in  FIG. 13 . The determined number of zones may be described as the zone count. In the expression indicated in  FIG. 13 , the zone count is calculated as the value obtained by dividing the difference between the data length of the outermost track and the data length of the innermost track by a data length equal to an interval at which the converter  201  obtains the head numbers and track numbers of sectors and adding 1 to the division result. For example, the zone count may be “((data length of outermost track)−(data length of innermost track))÷(interval at which sectors are identified)+1”. 
     For example, the maximum value of the data lengths of the blocks may be 512 kilobytes, which is an approximate value of the calculated data length of the outermost track. For example, the minimum value of the data lengths of the blocks may be 256 kilobytes, which is an approximate value of the calculated data length of the innermost track. When, for example, the minimum value of the data lengths in data processing executed by the controller  100  is 64 kilobytes, the zone count is 5 obtained by ((512−256)÷64+1=5). Accordingly, the zone count determining unit  204  determines that the entire data area is to be divided into five zones. 
     After the zone count determining unit  204  has determined the zone count, a zone number is assigned to each zone as an identifier that identifies the zone. The zone number may be a serial number unique to a particular zone. For example, the zone number of the outermost zone may be set to 0, and the zone number of a zone that is one zone inside the zone having the zone number 0 may be set to 1. Zone numbers may be assigned similarly up to the innermost zone so that zone numbers 0 to 4 are assigned to identify the five zones. The zones corresponding to the zone numbers 0 to 4 may be described as zones #0 to #4. 
     After the zone count and zone numbers have been determined, the block data length determining unit  205  determines a data length per block for each zone determined by the zone count determining unit  204 . 
     The block data length determining unit  205  determines the data length of the blocks in zone #0 to be 512 kilobytes, which is the maximum value of the data lengths of the blocks. The block data length determining unit  205  determines the data length of the blocks in zone #1 to be 448 kilobytes, which is obtained by subtracting 64 kilobytes from 512 kilobytes. The data lengths of the blocks in the other zones are determined similarly. For example, the data length of the blocks in zone #4 may be determined to be 256 kilobytes, and a 64-kilobyte longer data length may be assigned to blocks each time the zone number is decreased by one. 
     After a data length per block has been determined for each zone, the block data length determining unit  205  stores the data length in the zone information storage unit  211  in correspondence to the zone number of the zone. 
       FIG. 14  illustrates an example of information stored in the zone information storage unit  211 . The data length per block in each zone may be stored in the zone information storage unit  211  in a data structure as illustrated in zone information  1400  in  FIG. 14 . 
     After the zone count and the data length per block in each zone have been determined, the data area calculating unit  206  obtains a ratio by which each zone occupies the entire data area on a platter included in the magnetic disk storage unit. 
       FIG. 15  indicates an expression to calculate a ratio of a data area. The expression in  FIG. 15  obtains a ratio of a data area allocated for each zone to the entire data area. The zone count indicates the number of zones in the entire data area. The zone number indicates the number assigned to a zone during the execution of the procedure, described above, for dividing the data area. 
     In zone #0, for example, since the zone count is 5 and the zone number is 0, a ratio of the data area occupied by zone #0 to the entire data area is determined to be 36% according to the expression in  FIG. 15 . The data area calculating unit  206  stores the calculated ratio in the zone information storage unit  211  in correspondence to the zone number. 
     As for zones other than zone #0 as well, a ratio of the data area occupied by each zone to the entire data area is determined similarly, and the determination result is stored in the zone information storage unit  211 . 
       FIG. 16  illustrates an example of information stored in the zone information storage unit  211 . Data area information  1600  illustrated in  FIG. 16  may be stored in the zone information storage unit  211 . 
     The data length of each block is determined by the procedure described above when the data area of the magnetic disk storage unit is divided. Access speeds in blocks in outer tracks are faster than access speeds in blocks in inner tracks, so the blocks in the outer tracks are divided so that a longer data length is set for each block when compared with the blocks in the inner tracks. Accordingly, when, for example, a case in which data is read from a block in an outer track and a case in which data having the same data length as the above data is read from a block in an inner track are compared, the number of I/O accesses to the block in the outer track is smaller than in the inner track. This may reduce a processing load on the storage unit. 
     The outer on the platter the track is, the longer the data length of each block in the track is. The inner on the platter the track is, the shorter the data length of each block in the track is. Access speeds in blocks in inner tracks on a platter are slower than access speeds in blocks in outer tracks on the platter, so the blocks in the inner tracks are divided so that the data lengths per block are set to small values according to the degree of reduction in the access speed. This may reduce variations in times taken to access data in different blocks. 
       FIG. 17  illustrates an example of a hardware structure. In the storage unit in  FIG. 17 , one controller  100  and five magnetic disk storage units  1710 ( 1 ) to  1710 ( 5 ) are mutually coupled through a network  1720 . Redundant arrays of inexpensive disks (RAID) or redundant arrays of independent disks (RAID) 5 (4+1) may be applied. 
     The data area in a magnetic disk storage unit may have been evenly divided into 0x80-sector areas. The magnetic disk storage units  105  and  106  illustrated in  FIG. 1  and the magnetic disk storage units  1710 ( 1 ) to  1710 ( 5 ) may be substantially identical or similar hardware. The network  1720  may be, for example, a fiber channel or an SAN. 
     For example, an access to data stored in zone #4 may be made. The data length per block in zone #4 illustrated in  FIG. 16  may be 256 or 64 kilobytes. 
     In the form of RAID 5 (4+1), sequential read/write accesses may be made in a magnetic disk storage unit. 
       FIGS. 18 and 19  each illustrate examples of magnetic disk storage units. In  FIGS. 18 and 19 , sequential read/write accesses are made in the magnetic disk storage units. 
     In  FIG. 18 , the data area on each platter is divided into 64-kilobyte areas. Accordingly, to read data from four times 0x200 sectors, 20 I/O accesses may be made in the entire magnetic disk storage unit. 
     In  FIG. 19 , the data area on each platter is divided into 256-kilobyte areas. Therefore, to read data from four times 0x200 sectors, four I/O accesses may be made in the entire magnetic disk storage unit. When compared with the case in  FIG. 18 , the number of I/O accesses is reduced and the processing load on the storage unit may be reduced. Since 256 kilobytes is an approximate value of the data length per track in zone #4, although the data length per block is increased, the number of seeks performed by the magnetic head to scan sectors and a time taken for the seeks may be reduced. 
     In a magnetic disk storage unit, access performance involved in sequential read/write accesses may be improved. 
       FIGS. 20 and 21  each illustrate examples of magnetic disk storage units. In  FIGS. 20 and 21 , random read/write accesses are made in the magnetic disk storage units. 
     When, for example, the data area on each platter is divided into 64-kilobyte areas, four I/O accesses may be made to read data from 0x200 sectors in the entire magnetic disk storage unit. Data is divided into 64-kilobyte segments and is stored in four magnetic disk storage units, so an I/O access may be made in each of the four magnetic disk storage units. 
     In the case of a magnetic disk storage unit, the data area on a platter may be divided into 256-kilobyte areas. Accordingly, the number of I/O accesses to be made to read data from 0x200 sectors is 1 in the entire magnetic disk storage unit, so the number of I/O accesses may be reduced. Since 256 kilobytes is an approximate value of the data length per track in zone #4, although the data length per block is increased, the number of seeks performed by the magnetic head to scan sectors and a time taken for the seeks may be reduced. 
     In a magnetic disk storage unit, access performance involved in random read/write accesses may be improved. 
     For example, in the form of RAID 5 (4+1) illustrated in  FIG. 17 , the number of seeks performed by the magnetic head to scan sectors, a time taken for the seeks, and I/O accesses may be reduced. The processing load on the controller  100  may be reduced due to the reduction in I/O accesses. 
     An access to data stored in zone #4 may be made. For zones other than zone #4 as well, a data length per block may be determined according to the data length per track in each zone. Accordingly, access performance in zones other than zone #4 may be improved. 
     The data length per track on a platter included in the magnetic disk storage unit may be automatically calculated. The storage area in the magnetic disk storage unit may be suitably divided by using the automatically calculated data length per track. 
     All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiments of the present invention have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.