Abstract:
A data erasing method of the present disclosure is a data erasing method for erasing data stripe-recorded in a plurality of write-once optical discs constituting a redundant arrays of inexpensive disks (RAID) system and each including a plurality of data recording blocks and a redundant data block. In the data erasing method, alternate recording of at least one target block and the redundant data block is performed in a predetermined alternate area. The target block is one of the data recording blocks in which target data as erase target data is recorded. The target block is overwritten such that the target data is not correctly read.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The present disclosure relates to a method for erasing data recorded in a redundant arrays of inexpensive disks (RAID) system in which a plurality of write-once optical discs are used. 
         [0003]    2. Description of Related Art 
         [0004]    A write-once optical disc such as a DVD-R and a BD-R is a recording medium in which a recording mark recorded once cannot be rewritten. Unexamined Japanese Patent Publication No. 2002-245635 discloses an optical disc data erasing device that erases data recorded in the write-once optical disc. 
         [0005]    The optical disc data erasing device of Unexamined Japanese Patent Publication. No. 2002-245635 overwrites the recorded data by irradiating the recorded data with a laser beam having recording power during the recording, which allows the recorded data to be erased. Therefore, the erased point becomes unreadable. 
         [0006]    On the other hand, because the optical disc is an exchangeable recording medium, a defect can exist on a recording surface due to dust or a flaw. For this reason, in an optical disc drive that performs recording and reproduction on the optical disc, generally, defect management is performed in order to ensure reliability of the recorded or reproduced data (for example, see Unexamined Japanese Patent Publication No. 2011-154777). 
         [0007]    Additionally, the RAID system can be configured by using a plurality of optical discs in order to improve the reliability. In a recording device of International Patent Publication No. 2013/005418, a plurality of recording mediums are accommodated in a magazine, the recording medium in the magazine is carried to a plurality of drive units in the recording device, and a RAID controller that performs parallel recording on the plurality of recording mediums is provided. This allows the RAID system to be configured on a magazine-by-magazine basis. 
       SUMMARY 
       [0008]    The present disclosure provides a data erasing method for erasing data stripe-recorded in a plurality of write-once optical discs constituting a RAID system. 
         [0009]    The data erasing method of the present disclosure is the data erasing method for erasing the data stripe-recorded in the plurality of write-once optical discs constituting the RAID system and each including a plurality of data recording blocks and a redundant data block. In the data erasing method, alternate recording of at least one target block and the redundant data block is performed in a predetermined alternate area. The target block is one of the data recording blocks in which target data as erase target data is recorded. The target block is overwritten such that the target data is not correctly read. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0010]      FIG. 1  is a configuration diagram illustrating a system according to a first exemplary embodiment; 
           [0011]      FIG. 2  is a diagram illustrating a configuration of an optical disc RAID of the first exemplary embodiment; 
           [0012]      FIG. 3  is a diagram illustrating file system management information of the first exemplary embodiment; 
           [0013]      FIG. 4A  is a diagram illustrating alternate management information of the first exemplary embodiment; 
           [0014]      FIG. 4B  is a diagram illustrating the alternate management information of the first exemplary embodiment; 
           [0015]      FIG. 5  is a flowchart illustrating file erasing processing of an application of the first exemplary embodiment; 
           [0016]      FIG. 6  is a flowchart illustrating sector erasing processing of an optical disc RAID system of the first exemplary embodiment; 
           [0017]      FIG. 7  is a flowchart illustrating file erasing processing of an application according to a second exemplary embodiment; 
           [0018]      FIG. 8A  is a diagram illustrating alternate management information when a plurality of files of the second exemplary embodiment are erased; 
           [0019]      FIG. 8B  is a diagram illustrating alternate management information when the plurality of files of the second exemplary embodiment are erased; 
           [0020]      FIG. 8C  is a diagram illustrating alternate management information when the plurality of files of the second exemplary embodiment are erased; 
           [0021]      FIG. 8D  is a diagram illustrating alternate management information when the plurality of files of the second exemplary embodiment are erased; and 
           [0022]      FIG. 9  is a diagram illustrating an outline of data erase in the optical disc RAID system. 
       
    
    
     DETAILED DESCRIPTION 
       [0023]    Hereinafter, exemplary embodiments will be described in detail with reference to the drawings. However, the detailed description more than necessary is occasionally omitted. For example, the detailed description of an already known item or overlapping description of a substantially identical configuration is occasionally omitted. This is because unnecessary redundancy of the following description is avoided to facilitate understanding of those skilled in the art. 
         [0024]    The inventors provide the accompanying drawings and the following description in order that those skilled in the art fully understand the present disclosure, but it is noted that the subject matter of claims is not limited to the drawings and the description. 
         [0025]    (Background of One Aspect of the Present Disclosure) 
         [0026]      FIG. 9  is a diagram illustrating an outline of data erase in a RAID system (hereinafter, referred to as an optical disc RAID system) in which a plurality of write-once optical discs are used. Write-once optical discs  901 ,  902 ,  903 ,  904  constitute a system of RAID  5 . Sectors are arranged on the write-once optical disc. For example, sectors having addresses D 10 , D 11 , D 12 , D 13  are arranged on optical disc  901 . Addresses A 1  to A 12  are allocated to the RAID system. Addresses P 1 , P 2 , P 3 , P 4  are sectors in each of which the parity is stored. File  1  is recorded in sector group  905 , and file  2  is recorded in sector group  906 . 
         [0027]    In the case where file  1  is read from the RAID system, sector contents of addresses A 1 , A 2 , A 3 , A 4  of the RAID system can be read. This corresponds to the case where addresses D 10 , D 11  of optical disc  901 , address D 20  of optical disc  902 , and address D 30  of optical disc  903  are read. In the case where address A 2  cannot be reproduced, the RAID system reproduces address A 2  by restoring the content of address A 2  from the contents of addresses A 1 , A 3 , and parity P 1 . That is, even if it is not possible to read from one optical disc, the RAW system ensures readable redundancy. 
         [0028]    In the case where file  1  is erased, addresses A 1  to A 4 , where file  1  is stored, are erased. However, even if the erase is performed on the address A 4 , file  1  can be restored from addresses A 5 , A 6 , and parity P 2 . Therefore, file  1  is not completely erased. 
         [0029]    Also, for example, assume the case where address A 5  cannot be read during the reproduction of file  2  after the erase of file  1 . In this case, in an attempt to restore the content of address A 5 , reproduction of addresses A 4 , A 6 , and parity P 2  will be tried. However, address A 4  cannot be reproduced because address A 4  is already erased. Thus, a read error occurs, and it is impossible to restore the content of address A 5 . That is, the redundancy degrades. 
         [0030]    The present disclosure provides a method for erasing the recorded data while ensuring the redundancy of the RAID system in which the plurality of write-once optical discs are used. 
       First Exemplary Embodiment 
       [0031]      FIG. 1  is a diagram illustrating a configuration of a first exemplary embodiment in a data erasing method of the optical disc RAID system. In  FIG. 1 , server  107  operates as application  110 , small computer system interface (SCSI) library  108 , and universal disk format (UDF) driver  109 . More specifically, server  107  includes a CPU, a memory, and a hard disk drive (HDD). Various programs are stored in the HDD. The CPU reads various programs from the HDD onto the memory, and executes the programs, whereby the CPU operates as application  110 , SCSI library  108 , and UDF driver  109 . 
         [0032]    Server  107  is connected to optical disc RAID system  111 . Using a SCSI command, application  110  controls optical disc RAID system  111  through SCSI library  108  or UDF driver  109 . 
         [0033]    Optical disc RAID system  111  includes controller  101 , a plurality of drives  102 , magazine  104 , a plurality of optical discs  105 , magazine carrying mechanism  103 , and optical disc carrying mechanism  106 . In the first exemplary embodiment, optical disc RAID system  111  includes four drives  102 . 
         [0034]    Application  110  records the file in optical disc  105  of magazine  104  in the following way. The case where files  1 ,  2  are recorded is described by way of example. 
         [0035]    Application  110  issues a command to controller  101  of optical disc RAID system  111  through SCSI library  108  to load optical disc  105  of magazine  104  on drive  102 . Controller  101  issues an instruction to magazine carrying mechanism  103  to carry magazine  104  to a loading position. Magazine carrying mechanism  103  carries magazine  104  to the loading position where optical disc  105  can be loaded on drive  102 . Then, controller  101  issues an instruction to optical disc carrying mechanism  106  and drive  102  to load optical disc of magazine  104  on drive  102 . Optical disc carrying mechanism  106  moves optical disc  105  from magazine  104  to drive  102 . Drive  102  loads optical disc  105  thereon, and performs startup processing such that the recording and reproduction can be performed. Controller  101  repeats the above pieces of processing to load all optical discs  105  in magazine  104  on drives  102 . The plurality of loaded optical discs  105  are regarded as one optical disc RAID. In the first exemplary embodiment, four optical discs  105  loaded on four drives  102  constitute the optical disc RAID. In the first exemplary embodiment, a RAID level is RAID  5 . 
         [0036]    Then, application  110  issues an instruction to UDF driver  109  to record files  1 ,  2 . Pursuant to a UDF standard, UDF driver  109  searches a free sector on the optical disc RAID configured with the plurality of optical discs  105 , and records the pieces of data of files  1 ,  2  on the optical disc RAID. At the same time, UDF driver  109  records file names and recording addresses of files  1 ,  2  in file system management information on the optical disc RAID. The file system management information is recorded on the optical disc RAID upon the pursuant to the UDF standard. 
         [0037]      FIG. 3  is a diagram illustrating an example of the file system management information. It is assumed that file  1  has a size of 8 kbyte, that file  2  has a size of 10 kbyte, and that the sector has capacity of 2 kbyte in the optical disc RAID system. In this case, UDF driver  109  searches the free sector on the optical disc RAID, records file  1  in addresses A 1  to A 4  on the optical disc RAID, and records file  2  in addresses A 5  to A 9  on the optical disc RAID. At this point, the file system management information in  FIG. 3  is obtained. 
         [0038]    UDF driver  109  issues an instruction to controller  101  of optical disc RAID system  111  to record the pieces of data of files  1 ,  2  in addresses A 1  to A 4  and addresses A 5  to A 9  on the optical disc RAID. 
         [0039]    The operation of controller  101  in recording files  1 , file  2  in addresses A 1  to A 9  on the optical disc RAID will be described below with reference to  FIG. 2 . For convenience, optical discs  105  loaded on four drives  102  are referred to as optical discs  201 ,  202 ,  203 ,  204 . That is, optical disc RAID system  111  constitutes the system of RAID  5  using optical discs  201 ,  202 ,  203 ,  204 . The sectors are arranged on each optical disc. For example, the sectors having addresses D 10 , D 11 , D 12 , D 13  are arranged on optical disc  201 . Addresses A 1  to A 12  and addresses P 1  to P 4  are allocated as the RAID system to each optical disc. Addresses P 1 , P 2 , P 3 , P 4  are sectors in each of which the parity is stored. That is, addresses P 1 , P 2 , P 3 , P 4  are redundant data sectors. An alternate area is reserved on each optical disc. For example, alternate areas D 1 S 0 , D 1 S 1 , D 1 S 2  are reserved on optical disc  201 . The address of the optical disc RAID is not allocated to the alternate area. The alternate area is used in the case where a defect exists on the optical disc or where the erase described later is performed. 
         [0040]    In the case where controller  101  records the data in addresses A 1  to A 9  on the optical disc RAID, controller  101  issues an instruction to drive  102  to record the data, which should be recorded in addresses A 1 , A 2 , A 3  of the optical disc RAID, in address D 10  of optical disc  201 , address D 20  of optical disc  202 , and address D 30  of optical disc  203 . At the same time, controller  101  calculates the parity of RAID  5  based on the data recorded in addresses A 1 , A 2 , A 3 . Controller  101  issues an instruction to drive  102  to record the parity in address D 40  of optical disc  204 . The above operation is repeated with respect to addresses A 4  to A 6 , A 7  to A 9 , P 2 , P 3  on the optical. disc RAID, thereby recording the pieces of data and parities in optical discs  201 ,  202 ,  203 ,  204 . 
         [0041]    Then, UDF driver  109  issues an instruction to controller  101  of optical disc RAID system  111  to record the file system management information (see  FIG. 3 ). Controller  101  records the file system management information on the optical disc RAID. 
         [0042]    A method for erasing file  1  will be described below with reference to  FIGS. 4A, 4B, 5, 6 . Similarly to the recording of the file, application  110  loads the optical disc  105  of magazine  104  on drive  102  in advance.  FIG. 5  is a flowchart illustrating an operation in which application  110  erases the file. The case where application  110  erases file  1  is described by way of example. In step S 51 , application  110  issues a command to optical disc RAID system  111  through SCSI library  108  to read the file system management information about file  1 . In step S 52 , application  110  acquires a recording address of the data of file  1  from the file system management information. In the case where the file system management information is the contents in  FIG. 3 , the recording address of the data of the file  1  constitutes A 1  to A 4 . In step S 53 , application  110  issues an erase command to controller  101  of optical disc RAID system  111  through SCSI library  108  to erase addresses A 1  to A 4  in which the data of file  1  is written, thereby erasing the data of file  1 . In step S 54 , when the erase is completed with respect to all the target files, application  110  ends the erase operation. Unless all the target files are erased, the flow returns to step S 51 , and application  110  erases the next file. 
         [0043]      FIG. 6  is a flowchart illustrating an operation in which controller  101  executes the erase command. In step S 61 , when receiving the erase command from application  110 , controller  101  determines whether a whole range of a RAID stripe is included in the address range which is included in the erase command and the data in which should be erased. As used herein, the RAID stripe is a minimum unit in performing stripe recording on the optical disc constituting the RAID, and is a combination of the addresses necessary for the calculation of the parity. The address range of the RAID stripe is addresses A 1  to A 3 , addresses A 4  to AG, addresses A 7  to A 9 , and addresses A 10  to A 12  in  FIG. 2 . For example, in the case where the address range specified from the application is addresses A 1  to A 4 , controller  101  determines that the whole of addresses A 1  to A 3  constituting one RAID stripe is included in step S 61 . That is, controller  101  determines that the address range of the erase command includes the whole range of the RAID stripe (Yes in step S 61 ). In this case, in step S 62 , controller  101  issues an instruction to drive  102  to erase address D 10  of optical disc  201 , address D 20  of optical disc  202 , and address D 30  of optical disc  203  in order to erase addresses A 1  to A 3  extracted in step S 61 . Drive  102  erases the specified addresses. When the address range of the erase command includes the whole range of the RAID stripe, controller  101  erases all the addresses. When the erase is completed, the flow goes to step S 63 . In step S 61 , when controller  101  determines that the address range including the whole range of the RAID stripe does not exist (No in step S 61 ), the flow goes to step S 63 . 
         [0044]    In step S 63 , controller  101  determines whether the address range of the received erase command includes only a partial range of the RAID stripe. When determining that the address range of the erase command does not include only the partial range of the RAID stripe (No in step S 63 ), controller  101  ends the processing. On the other hand, for example, in the case where the address range specified from the application is addresses A 1  to A 4 , controller  101  determines that address A 4  corresponds only to a part of the RAID stripe in step S 63 . That is, controller  101  determines that the address range of the erase command includes only the partial range of the RAID stripe (Yes in step S 63 ). In this case, in step S 64 , controller  101  erases address A 4  that is a part of the RAID stripe. In step S 65 , controller  101  performs alternate recording on address A 4  using data having a content of 0. Specifically, controller  101  issues an instruction to drive  102  to erase address D 11  of optical disc  201 , and drive  102  erases the specified address. Controller  101  also issues an instruction to drive  102  to perform the alternate recording on address D 11  of optical disc  201  using the data having the contents of all 0. Drive  102  selects free alternate area D 1 S 0  from the alternate areas of optical disc  201 , and performs the recording on alternate area D 1 S 0  with the contents of all 0. That is, drive  102  records the data having bits of all 0 in alternate area D 1 S 0 . Drive  102  registers information indicating that address D 11  of optical disc  201  is replaced with alternate destination D 1 S 0  in the alternate management information (see  FIG. 4A ) about optical disc  201 , and also records the alternate management information in optical disc  201 . In the case where access to address D 11  is made thereafter, drive  102  accesses address D 1 S 0  instead of address D 11  based on the alternate management information. In step S 65 , instead of the alternate recording with the contents of all 0, the alternate recording may be performed with all the contents of 1, or the alternate recording may be performed by replacing all the contents of 1 with another piece of predetermined data. 
         [0045]    Then, controller  101  recalculates the parity of the RAID stripe including the target address in step  566 . Controller  101  performs the alternate recording on the recalculated parity in step S 67 . In the case where address A 4  of file  1  is erased in step S 64 , controller  101  issues an instruction to drive  102  to read addresses A 4 , A 5 , A 6  of the RAID stripe including address A 4 . Drive  102  reads the contents of address D 11  of optical disc  201 , address D 21  of optical disc  202 , and address D 41  of optical disc  204 . Address D 11  of optical disc  201  is replaced with address D 1 S 0 . When reading address D 11 , drive  102  recognizes that address D 11  is replaced with address D 1 S 0  by referring to the alternate management information in  FIG. 4A . Drive  102  reads the content of address D 1 S 0  instead of address D 11 . Controller  101  recalculates the parity from the read content, and issues an instruction to drive  102  to perform the alternate recording on address D 31  of optical disc  203  with the recalculated parity. Drive  102  selects free alternate area D 3 S 0  from the alternate areas of optical disc  203 , and performs the recording on alternate area D 3 S 0  with the content of the recalculated parity. Drive  102  registers information indicating that address D 31  of optical disc  203  is replaced with alternate destination D 3 S 0  in the alternate management information (see  FIG. 4B ) of optical disc  203 , and also records the alternate management information in optical disc  203 . In the case where access to address D 31  is made thereafter, drive  102  accesses address D 3 S 0  instead of address D 31 . Controller  101  may erase the pre-recalculation parity in step S 68 . Specifically, controller  101  issues an instruction to drive  102  to erase address D 31  of optical disc  203 , and drive  102  may erase the specified address. The operation in step S 68  may be eliminated. 
         [0046]    The data of file  1  recorded in addresses A 1  to A 4  of the optical disc RAID can be erased through the above erase operation. Because both the alternate recording and the recalculation and recording of the parity are performed on address A 4  of the optical disc RAID, the original data of address A 4  cannot be restored from addresses A 5 , A 6 , and parity P 2 . That is, all the pieces of data of file  1  are erased from the optical disc RAID. 
         [0047]    In the optical disc RAID in which file  1  is erased in the above way, the redundancy identical to that of pre-erase file  1  can be ensured with respect to addresses A 5 , A 6  where a part of file  2  is recorded, because the recalculation and the alternate recording are performed on parity P 2  after the alternate recording is performed on address A 4  with the contents of all 0 or another piece of predetermined data. That is, according to the method for erasing the data on the optical disc RAID of the first exemplary embodiment, the data can be erased while the redundancy is ensured with respect to the data that is not erased. 
         [0048]    The data of parity P 2  (address D 31 ) of the alternate source in the alternate recording may be erased. In this case, controller  101  issues an instruction to drive  102  to erase address D 31  of optical disc  203  in addition to the recalculation and alternate recording (steps S 66 , S 67 ) of the parity, and drive  102  erases address D 31  (step S 68 ). Doing this can make it impossible to read the address D 31  before the replacement and to restore the contents of A 4  from the contents of addresses A 5 , A 6 , and thereby can erase file  1  more completely. 
       Second Exemplary Embodiment 
       [0049]    A second exemplary embodiment of the present disclosure will be described with reference to  FIGS. 7, 8A to 8D . In the second exemplary embodiment, the description of the component similar to the first exemplary embodiment is omitted. 
         [0050]      FIG. 7  is a flowchart illustrating a data erasing method, according to a second exemplary embodiment, that is an operation of application  110  that erases the plurality of files. In the second exemplary embodiment, the case where files  1 ,  2  recorded in the optical disc RAID are erased is described by way of example. 
         [0051]    Similarly to the recording of the file, application  110  loads optical disc  105  of magazine  104  on drive  102  in advance. 
         [0052]    In step S 71 , application  110  issues a command to optical disc RAID system  111  through SCSI library  108  to read the file system management information about files  1 ,  2 . In step S 72 , application  110  acquires recording addresses of the pieces of data of files  1 ,  2  from the file system management information, and extracts consecutive data write addresses from the acquired recording addresses. In the case where the file system management information has the contents in  FIG. 3 , the recording address of the data of file  1  is A 1  to A 4 , and the recording address of the data of file  2  is A 5  to A 9 . Therefore, the extracted consecutive data write addresses constitute A 1  to A 9 . In step S 73 , application  110  issues an erase command to controller  101  of optical disc RAID system  111  to erase extracted consecutive data write addresses A 1  to A 9 , thereby erasing the pieces of data of files  1 ,  2 . In step S 74 , when the erase is completed with respect to all the extracted consecutive data write addresses (Yes in step S 74 ), application  110  ends the erase operation. When the erase is not completed with respect to all the extracted consecutive data write addresses (No in step S 74 ), the flow returns to step S 73 , and application  110  erases the next data write addresses. 
         [0053]    Controller  101  operates according to the flowchart in  FIG. 6  in which the erase command is executed. In the case where the address specified from the application is addresses A 1  to A 9 , controller  101  determines that addresses A 1  to A 9  include the whole range of the RAID stripe in step S 61 . Specifically, controller  101  determines that addresses A 1 , A 2 , A 3 , addresses A 4 , A 5 , A 6 , and addresses A 7 , A 8 , A 9 , which constitute the RAID stripe, are included in the range of addresses A 1  to A 9 . In step  562 , controller  101  erases addresses A 1  to A 3 , A 4  to A 6 , A 7  to A 9  extracted in step  561 . Specifically, controller  101  issues an instruction to drive  102  to erase addresses D 10 , D 11 , D 12  of optical disc  201 . Controller  101  issues an instruction to drive  102  to erase addresses D 20 , D 21  of optical disc  202 . Controller  101  issues an instruction to drive  102  to erase addresses D 30 , D 32  of optical disc  203 . Controller  101  issues an instruction to drive  102  to erase addresses D 41 , D 42  of optical disc  204 . Drive  102  erases each specified address. 
         [0054]    In step  563 , controller  101  determines whether the address range of the received erase command includes only a partial range of the RAID stripe. However, in the case where the address range specified from the application is addresses A 1  to A 9 , controller  101  determines that address range including only the part of the RAID stripe does not exist in step S 63 , and the erase operation is completed. 
         [0055]    Through the above erase operation, the file can be erased while consumption of the alternate area is suppressed. In the case where files  1 ,  2  are erased, the alternate area is not consumed. On the other hand, in the case where files  1 ,  2  are erased based on the first exemplary embodiment, like pieces of alternate management information of optical discs  201  to  204  in  FIG. 8A  to  FIG. 8D , the alternate recording occurs with respect to address A 4  of the optical disc RAID, namely, address D 11  of optical disc  201  and parity P 2 , namely, address D 31  of optical disc  203  in order to erase file  1 . The alternate recording occurs with respect to addresses A 5 , P 2 , A 6  of the optical disc RAID, namely, address D 21  of optical disc  202 , address D 31  of optical disc  203 , and address D 41  of optical disc  204  in order to erase file  2 . 
         [0056]    On the other hand, in the second exemplary embodiment, controller  101  operates so as to simultaneously erase the plurality of files. In the second exemplary embodiment, controller  101  can determine that the address range of the erase command includes the whole range of the RAID stripe configured with address A 4  where the data of file  1  is recorded and addresses A 5 , A 6  where the data of file  2  is recorded. Accordingly, the data can be erased with respect to addresses A 4 , A 5 , A 6  without performing the alternate recording. 
         [0057]    Thus, in the method for erasing the data on the optical disc RAID of the second exemplary embodiment, the consumption of the alternate area is suppressed in erasing the data, so that the data can be erased while the reliability is ensured. 
       Other Exemplary Embodiments 
       [0058]    The first and second exemplary embodiments are described above as an example of the technology disclosed in the present application. The technology of the present disclosure is not limited to the first and second exemplary embodiments, but the technology can also be applied to exemplary embodiments in which changes, replacements, additions, and omissions are made. A new exemplary embodiment can be made by a combination of the components described in the first and second exemplary embodiments. 
         [0059]    Therefore, other exemplary embodiments are illustrated below. 
         [0060]    In the first and second exemplary embodiments, in the case where the address range of the erase command includes only the part of the RAID stripe, the alternate recording is performed by recording the contents of all 0 in the address of the alternate destination during the erase and alternate recording of the data. Alternatively, the data is not recorded in the address of the alternate destination, but an address that does not exist on the optical disc may be registered as an alternate destination address of the alternate management information. In this case, in the case where a request to reproduce the address where the address that does not exist on the optical disc is registered as the alternate destination address is made to drive  102 , drive  102  returns the contents of all 0 as a reproduction result. Since this will eliminate the need to consume the alternate area, the alternate area for the erase can further be reduced. The address that does not exist on the optical disc is registered in the above description. Alternatively, an item of an alternate attribute is added to the alternate management information, the alternate recording is not performed as the alternate attribute, and an attribute indicating that the contents of all 0 are returned may be recorded in the case where access to the alternate source address is made. 
         [0061]    In the first and second exemplary embodiments, the alternate area provided on the optical disc is used. Alternatively, in the case where the erase is performed as the optical disc RAID, the larger alternate area may be secured during formatting of the optical disc compared with an optical disc constituting the optical disc RAID in which the erase of the present disclosure is not performed (the alternate recording is performed on a defect area). This will enable securing as much alternate area for the defects as the optical disc RAID in which the erase is not performed, while securing the alternate area for the erase. 
         [0062]    In the first and second exemplary embodiments, the alternate area provided on the optical disc is used when the defect exists on the optical disc and when the erase is performed. Alternatively, the alternate area used in existence of the defect and the alternate area used to perform the erase may separately be reserved. This can guarantee the number of times of reliably performing the erase. 
         [0063]    In the first and second exemplary embodiments, the configuration of the optical disc RAID having the level of RAID  5  with four optical discs are used is described by way of example. Additionally, the present disclosure can also be applied to the configuration of the optical disc RAID having the level of RAID  5  or RAID  6  with five optical discs. In this case, the size of the alternate area to be reserved may be changed depending on a kind of the RAID, for example, RAID  5  or RAID  6 . For RAID  6 , the larger alternate area is required because of the parity increases. This can secure the number of times of performing the erase irrespective of the kind of the RAID that is used. 
         [0064]    In the first and second exemplary embodiments, the alternate area reserved on the optical disc is used in the alternate recording. Alternatively, like pseudo over write (POW) defined by a UDF 2.6 standard, the alternate recording may be performed on a data area that is not the alternate area on the optical disc. This can eliminate the need to secure the alternate area for the erase during the formatting of the optical disc, and can enable the erase by managing a free space according to the necessity for the erase after the formatting. 
         [0065]    In the first exemplary embodiment, in step  65 , the alternate recording of the target sector is performed in the predetermined alternate area while the target data of the target sector is replaced with the predetermined data. Alternatively, in the plurality of write-once optical discs, the alternate destinations of the target sectors on the identical write-once optical disc may be identified, with each other. This can reduce the alternate area. 
         [0066]    Because the exemplary embodiment is used to illustrate the technology of the present disclosure, various changes, replacements, additions, and omissions can be made in claims or a range equivalent to the claims.