Read device for processing a read error, system, its method, and program

[Technical field]

0001The present invention relates to a technique for continuing to read data rapidly and appropriately when an unrecoverable read error occurs in a tape reader connected to a host computer.

[Background art]

0002In a tape drive for reading digital data from a magnetic tape, part of data recorded on the magnetic tape may be unreadable for some reason. When an unrecoverable read error occurs, the conventional tape drive reports the read error to the host computer, and once ends reading. To continue reading data, an application of the host computer needs to avoid a part where the error occurs and read data after it.

0003By the way, the host computer manages the reading position of data based on how many records as the minimum unit of data as seen from the host computer and how many format marks indicating the boundary of record block are read. On the other hand, the tape drive records data in data units different from the host computer on the magnetic tape. Therefore, the data unit includes a plurality of records and file marks. However, the length of record is not necessarily fixed. Also, the tape drive often records data after compressing data received from the host computer. Therefore, when the data unit is unreadable for some reason, the host computer cannot know the number of records and the number of file marks included in the data.

0004Thus, to avoid a part where the error occurs, the host computer needs to perform a method of 1) moving the reading position forward by small steps and trying the readability of data at every step, or 2) moving the reading position to the sufficiently far position and starting reading. However, with the method of 1), many tries are necessary, and it takes a long time to read. On the other hand, with the method of 2), data that is originally readable may be canceled.

0005The conventional technique for conveying the next readable data position to the host computer when an unrecoverable error occurs was described in Patent Document 1, for example. The Patent Document 1 deals with a tape drive unit conforming to the Advanced Intelligent Tape (AIT) standards for recording or reproducing data via the tape by handling data in group units, and a host system for controlling the tape drive unit. And the Patent Document 1 discloses a technique in which the beginning of group and the beginning of sector are made coincident in allotting data in group units to sector units of the minimum processing units of the host system, and when a reproduction error occurs, the first record number of group and the error information for every frame making up the group are only returned from the tape drive unit to the host system, and the error sector can be computed on the side of the host system.

0006Patent Document 1: Published Unexamined Patent Application No. <patcit id="pcit0001" dnum="WO2002251843A"><text>2002-251843</text></patcit> (pages 4 and 5, page 8)

[Disclosure of the invention]

[Problems to be solved by the invention]

0007However, the technique as disclosed in Patent Document 1 presupposes that the length of data recorded on the magnetic tape can be converted to the data length handled by the host computer. Therefore, in the case where the length of record in the minimum data unit as seen from the host computer is variable, or the tape drive compresses data from the host computer and records it in the magnetic tape, the technique of Patent Document 1 can not be used, whereby it is still difficult to find the next readable position in the host computer rapidly and suitably.

0008Thus, it is an object of the invention to provide a tape reader, system, method and program that can solve the above-mentioned problems.

[Means for solving the problems]

0009In order to accomplish the above object, the invention provides a tape reader for processing a data read error from a tape medium as follows. This tape reader comprises a data reading section for reading data in every data unit of data reading unit from the tape medium, a reading control section for controlling the data reading section to read data in accordance with a command from a host computer, and on condition that an error occurs in reading the data unit, to skip an error data unit where the error occurs and read the next readable data unit immediately after the error data unit, a computation section for computing the number of records and the number of boundary marks included in the error data unit where the error occurs from the information on the records and boundary marks included in the data unit preceding to the error data unit that is read immediately before the error occurs, and the information on the records and boundary marks included in the data unit next to the error data unit, the boundary marks indicating the boundary of record block, and a communication section for sending the number information on the computed number of records and the computed number of boundary marks to the host computer.

0010Preferably, the information on the records and boundary marks held in the data unit preceding to the error data unit includes the number of records and the number of boundary marks included in the data unit preceding to the error data unit and the number of records and the number of boundary marks counted from the beginning of the tape medium to the data unit preceding to the error data unit. Also, the information on the records and boundary marks held in the data unit next to the error data unit includes the number of records and the number of boundary marks counted from the beginning of the tape medium to the error data unit where the error occurs.

0011In this case, a value of subtracting the number of records counted from the beginning of the tape medium to the data unit preceding to the error data unit from the number of records counted from the beginning of the tape medium to the error data unit where the error occurs is obtained. And if the number of records included in the data unit preceding to the error data unit is further subtracted from this value, the number of records included in the error data unit where the error is detected can be obtained. The number of boundary marks can be likewise obtained.

0012Further, preferably, the tape medium and the tape reader conform to the Linear Tape Open (LTO) standards. And the information on the records and boundary marks included in the data unit preceding to the error data unit is acquired from a Data Set Information Table (DSIT) describing the contents of data unit included in the data unit preceding to the error data unit. Also, the information on the records and boundary marks included in the data unit next to the error data unit is acquired from the DSIT included in the data unit next to the error data unit.

0013Also, preferably, the tape reader further comprises a generation section for generating dummy records for the computed number of records and boundary marks for the computed number of boundary marks, wherein the communication section sends the dummy records and the boundary marks generated as the number information to the host computer.

0014Further, preferably, the generation section generates the dummy records with the length of read data designated in a command issued from the host computer to the tape reader. Or the tape reader can be set a 0 byte block mode in which the length of dummy record is 0, and if the 0 byte block mode is set, the generation section generates the dummy record with the length of 0.

0015Also, preferably, the communication section communicates with the host computer in accordance with a Small Computer System Interface (SCSI) protocol. And the generation section generates the dummy records by deciding the length of dummy record based on FixedBit, Suppress Incorrect Length Indicator (SILI) Bit and TransferLength included in a Read command, and BlockLength included in BlockDescriptor sent in advance from the host computer together with a ModeSelect command.

0016Also, preferably, the communication section sends the dummy records and the boundary marks together with the dummy information indicating that data is dummy to the host computer. Further, preferably, the communication section communicates with the host computer in accordance with the SCSI protocol. And the communication section sends CheckCondition for informing occurrence of error and SenseData with MediumError set in SenseKey for informing the content of error to the host computer.

0017Also, preferably, the tape reader can be set either a normal operation mode of only returning a read error when the read error occurs, or a rescue mode of returning the number information on the number of records and the number of boundary marks included in the part where the read error occurs when the read error occurs is settable. Also, the host computer recognizes the data position from the number of records and the number of boundary marks received from the tape reader.

0018Also, in order to accomplish the above object, the invention is implemented by a system for processing a data read error from a tape medium, comprising a tape reader, and a host computer connected to the tape reader as follows. The tape reader comprises a receiving section for receiving a data reading command from the host computer, as well as the reading section, the reading control section, the computation section, the generation section and the sending section (part of the communication section) of the tape reader as described above. Also, the host computer comprises a sending section for sending the data reading command to the tape reader, a receiving section for receiving the number information on the computed number of records and the computed number of boundary marks, and a judgment section for judging the reading position of data based on the number information. If the dummy record and the boundary mark generated as the number information is sent together with the dummy information indicating that the data is dummy from the tape reader, the judgment section judges whether the received dummy record and the boundary mark are dummy based on the dummy information and judges the reading position of data.

0019Or the tape reader comprises a receiving section for receiving a data reading command from the host computer, the reading section and the reading control section of the tape reader as described above, a buffer for storing the data unit read by the reading section, and a sending section (part of the communication section as described above) for retrieving the first information on the records and boundary marks indicating the boundary of record block included in the data unit preceding to the error data unit that is read immediately before the error occurs and the second information on the records and boundary marks included in the data unit next to the error data unit from the buffer and sending them to the host computer. And the host computer comprises a sending section for sending the data reading command to the tape reader, a receiving section for receiving the first information and the second information, and a judgment section for judging the reading position of data by computing the number of records and the number of boundary marks included in the data unit where the error occurs based on the first information and the second information.

0020Though the invention has been described above as the tape reader for processing the data read error from the tape medium and the system for processing the data read error from the tape medium, the invention can be also grasped as a method, a program or a storage medium storing the program.

[Advantages of the invention]

0021With the invention, the length of record that the host computer writes on the tape medium is not necessarily constant, and even in the case where data is recorded on the tape medium after data compression, the host computer can estimate easily and appropriately how much data is included in the data unit on the tape medium where the read error occurs, if an unrecoverable read error occurs in reading data from the tape medium.

[Best mode for carrying out the invention]

0022A best mode for carrying out the present invention will be described below in detail with reference to the drawings. The following embodiments do not limit the invention as defined in claims, and all the combinations of features as described in the embodiments may not be requisite for solving means of the invention. Throughout the description of the embodiments, the same parts are designated by the same numerals.

0023<figref idref="f0001">Figure 1</figref> shows one example of the configuration of a system 10 for processing a data read error from a tape medium according to one embodiment of the invention. The system 10 for processing the data read error form the tape medium according to this embodiment is intended to allow a host computer 400 to estimate how much data is included in part of the tape medium 200 where an error occurs, even if the unrecoverable read error occurs when a tape reader 100 reads data from the tape medium 200 in accordance with a reading command from the host computer 400.

0024The system 10 for processing the read error comprises the tape reader 100 for reading data from the tape medium 200 and the host computer 400 connected to the tape reader 100. The tape reader 100 and the host computer 400 are connected via an SCSI interface or a network 300 such as a LAN (Local Area Network). Also, the tape reader 100 and the host computer 400 may be connected via a private line or the network 300 such as the Internet. The tape reader 100 may be connected to an information processing apparatus such as a personal computer via a communication interface such as the SCSI interface or the LAN, and connected to the network 300 via the information processing apparatus.

0025The tape reader 100 is a tape reading device conforming to the LTO (Linear Tape Open) standards, for example, and the tape medium 200 conforms to the LTO (Linear Tape Open) standards, for example. The LTO standards are the open format standards developed jointly by Hewlett-Packard Company, IBM Company and Quantum company.

0026The tape reader 100 reads data in every data unit that is a reading unit of data from the tape medium 200 in accordance with a data reading command from the host computer 400. When an error occurs in reading, the tape reader 100 skips reading an error data unit where the error occurs and reads the next readable data unit immediately after the error data unit. And the tape reader 100 computes how much data is included in the error data unit where the error occurs, more particularly, the number of records and the number of boundary marks indicating the boundary of record block included in the error data unit where the error occurs, from the information on the contents of data unit included in the data unit read preceding to the error data unit and the information on the contents of data unit included in the data unit next to the error data unit. The record and the boundary mark are in the minimum data unit for handling as seen from the host computer 400, and in the SCSI interface, the boundary mark is called a file mark. In the following, the boundary mark is described as the file mark.

0027The tape reader 100 generates the dummy records for the computed number of records and the files marks for the computed number of file marks, and sends them together with the dummy information indicating that the data is dummy to the host computer 400. The host computer 400 receives the dummy records and the file marks together with the dummy information, and judges whether or not the received dummy records and file marks are dummy based on the dummy information.

0028In the above way, the tape reader 100 computes the number of records and the number of file marks included in the data unit (possibly plural data units) where the read error occurs from data before and after a part of the tape medium where the read error occur, and passes the information on the computed numbers to the host computer 400, whereby the host computer 400 can estimate how many records and file marks are included in the part of the tape medium 200 where the error occurs. And since the tape reader 100 sends the number information on the number of dummy records and file marks to the host computer 400 herein, the reading of data is not terminated.

0029<figref idref="f0001">Figure 2(a)</figref> shows one example of the organization of a recording area in the tape medium 200 according to this embodiment. Herein, the tape medium 200 conforms to the LTO standards. In an LTO data format, the record and file mark received from the host computer 400 are once compressed, and then recorded on the tape medium 200 in units called a Data Set (DS) 201. The DSs 201 are numbered sequentially from the starting position of the tape medium 200, namely, Beginning Of Tape (BOT), as shown in <figref idref="f0001">Figure 2(a)</figref>. Also, each DS is composed of two areas, a data area 203 and a Data Set Information Table (DSIT) 205, as shown in <figref idref="f0001">Figure 2(b)</figref>. The data area 203 is the area for recording the data as the name implies, and the DSIT 205 describes the contents of the data area.

0030In the invention, to compute the number of records and the number of file marks included in the DS where the error occurs, the following information among plural pieces of information included in the DSIT 205, namely, the information including the number of DS 201 in which the DSIT 205 is included, the number of records and the number of file marks included in the DS 201, the number of records and the number of file marks included from the BOT to the immediately preceding DS 201, and a Tape Write Pass (TWP) is used. Herein, the TWP is used to judge whether or not the data is old, in which the value of TWP is 1 when data is firstly recorded, and incremented by 1 every time the data is overwritten.

0031Referring to <figref idref="f0001">Figure 3</figref>, a method for judging whether the data is new or old based on the TWP will be described below. The data is firstly recorded from DS#N-1 211 to DS#N+1 215 on the tape medium 200, as shown in <figref idref="f0001">Figure 3(a)</figref>. Since any DS is firstly written on the tape medium 200, the value of the TWP indicates 1. <figref idref="f0001">Figure 3(b)</figref> shows a state where data is overwritten on the tape medium 200. Seeing DS#N-1 211, the value of the TWP is incremented by 1 and equal to 2, because the data is overwritten. Then, seeing DS#N 213, the writing is disabled due to a damage on the surface of the tape medium 200. In accordance with the LTO standards, when data can not be written on the tape medium 200 for some reason, it is allowed to continue writing within four meters from a problematical part on the tape medium 200. Therefore, DS#N is overwritten at the position of DS#N+1 215 by skipping DS#N 213 where a problem occurs in <figref idref="f0001">Figure 3(b)</figref>. Since DS#N 215 is overwritten data, the value of the TWP is incremented by 1 and equal to 2.

0032Herein, if data is read from the tape medium 200 in the state of <figref idref="f0001">Figure 3(b)</figref>, two DSs have the same number N. Thus, the value of TWP is 1 in DS#N 213 while it is 2 in DS#N 215. Accordingly, the data of DS#N 215 having the larger value of TWP is new data. In this way, seeing the value of TWP in the LTO standards, it is possible to judge whether data is new or old. Though the tape medium 200 in the LTO standards has been described herein, the invention may be also applicable in accordance with the standards adopting a format of describing information corresponding to the information included in the DSIT for each data unit.

0033<figref idref="f0002">Figure 4</figref> shows one example of the functional configuration of the tape reader 100 according to this embodiment. The tape reader 100 comprises a communication section 110, a buffer 120, a reading section 130 and a controller 135. The controller 135 controls the whole of the tape reader 100, and further comprises a reading control section 140, a computation section 150, and a generation section 160. The communication section 110 communicates with the host computer 400 and may be recognized as a receiving section and a sending section. In the following, it is supposed that the communication between the tape reader 100 and the host computer 400 is performed via the SCSI interface. The communication section (receiving section) 110 receives a reading command from the host computer 400.

0034The reading section 130 reads data in every data or DS unit that is the data reading unit from the tape medium 200 and stores it into the buffer 120. The reading control section 140 controls the reading section 130 to read the data in accordance with a reading command from the host computer 400. When an error occurs in reading the DS, the reading control section 140 controls the reading section 130 to skip the DS where the error occurs and read and store the next readable DS immediately after the DS where the error occurs into the buffer 120. Taking the tape medium 200 as shown in <figref idref="f0002">Figure 5</figref> as an example, after the reading section 130 reads the DS 221, it skips the DS 223 (possibly plural DSs) where a read error occurs, and stores the next readable DS 225 immediately after the DS223 into the buffer 120.

0035The computation section 150 reads the information on the records and file marks included in the DS 221 preceding to the DS223 that is read immediately before the error occurs and the information on the records and file marks included in the DS 225 next to the DS223 from the buffer 120, and computes the number of records and the number of file marks included in the DS 223 (possibly plural DSs) where the error occurs. In the following, the computation will be described in detail.

0036The computation section 150 retrieves TWP_n, the number DS_n of DS 221, the number of records R_n and the number of file marks F_n included from the BOT to the immediately preceding DS, and the number of records r_n and the number of file marks f_n included in DS 221 from the DSIT of the DS 221 preceding to the DS223. Also, the computation section 150 retrieves TWP_m, the number DS_m of DS 221, the number of records R_m and the number of file marks F_m included from the BOT to the immediately preceding DS from the DSIT of the DS 225 next to the DS223.

0037Herein, the computation section 150 firstly confirms the continuity of read data between DS 221 and DS 225 before and after the error, before computing the number of records and so on included in the DS 223 (possibly plural DSs). The discontinuity of data occurs when a write error occurs due to a damage or the like on the surface of the tape medium 200 and consequently the old data remains in overwriting the data, for example, as described above. Since such old data should be canceled, the continuity of data is firstly confirmed in the invention.

0038The continuity of data can be confirmed using the following four conditional expressions. <maths id="math0001" num=""><math display="block"><msub><mi mathvariant="normal">R</mi><mi mathvariant="normal">m</mi></msub><mo mathvariant="normal">></mo><mo mathvariant="normal">=</mo><msub><mi mathvariant="normal">R</mi><mi mathvariant="normal">n</mi></msub></math><img file="EP2000897A2_D0001.tif" /></maths><maths id="math0002" num=""><math display="block"><msub><mi mathvariant="normal">F</mi><mi mathvariant="normal">m</mi></msub><mo mathvariant="normal">></mo><mo mathvariant="normal">=</mo><msub><mi mathvariant="normal">F</mi><mi mathvariant="normal">n</mi></msub></math><img file="EP2000897A2_D0002.tif" /></maths><maths id="math0003" num=""><math display="block"><msub><mi>TWP</mi><mi mathvariant="normal">m</mi></msub><mo mathvariant="normal">></mo><mo mathvariant="normal">=</mo><msub><mi>TWP</mi><mi mathvariant="normal">n</mi></msub></math><img file="EP2000897A2_D0003.tif" /></maths><maths id="math0004" num=""><math display="block"><msub><mi>DS</mi><mi mathvariant="normal">m</mi></msub><mo mathvariant="normal">></mo><msub><mi>DS</mi><mi mathvariant="normal">n</mi></msub></math><img file="EP2000897A2_D0004.tif" /></maths> If all the above four conditional expressions are satisfied for DS 221 and DS 225 before and after the error, it is said that DS 221 and DS 225 are continuous. If any one of the four conditional expressions is not satisfied, the computation section 150 cancels the DS 225 next to the DS223, and repeats the same check for the next DS read following the DS 225. Herein, it is supposed that the continuity of data between DS 221 and DS 225 is confirmed.

0039If the continuity of data is confirmed, the computation section 150 computes the number of records and the number of file marks included in the DS 223 (possibly plural DSs) where the error occurs. The following relational expression holds between the number of records R_n and the number of file marks F_n included from the BOT to the immediately preceding DS of the DS 221, and the number of records r_n and the number of file marks f_n included in DS 221. <maths id="math0005" num=""><math display="block"><msub><mi mathvariant="normal">R</mi><mrow><mi mathvariant="normal">n</mi><mo mathvariant="normal">+</mo><mn mathvariant="normal">1</mn></mrow></msub><mo mathvariant="normal">=</mo><msub><mi mathvariant="normal">R</mi><mi mathvariant="normal">n</mi></msub><mo mathvariant="normal">+</mo><msub><mi mathvariant="normal">r</mi><mi mathvariant="normal">n</mi></msub></math><img file="EP2000897A2_D0005.tif" /></maths><maths id="math0006" num=""><math display="block"><msub><mi mathvariant="normal">F</mi><mrow><mi mathvariant="normal">n</mi><mo mathvariant="normal">+</mo><mn mathvariant="normal">1</mn></mrow></msub><mo mathvariant="normal">=</mo><msub><mi mathvariant="normal">F</mi><mi mathvariant="normal">n</mi></msub><mo mathvariant="normal">+</mo><msub><mi mathvariant="normal">f</mi><mi mathvariant="normal">n</mi></msub></math><img file="EP2000897A2_D0006.tif" /></maths> Accordingly, the number of records r_x and the number of file marks f_x included in the DS 223 (possibly plural DSs) where the error occurs can be obtained from the following expressions. <maths id="math0007" num=""><math display="block"><msub><mi mathvariant="normal">r</mi><mi mathvariant="normal">x</mi></msub><mo mathvariant="normal">=</mo><msub><mi mathvariant="normal">R</mi><mi mathvariant="normal">m</mi></msub><mo mathvariant="normal">-</mo><msub><mi mathvariant="normal">R</mi><mi mathvariant="normal">n</mi></msub><mo mathvariant="normal">-</mo><msub><mi mathvariant="normal">r</mi><mi mathvariant="normal">m</mi></msub></math><img file="EP2000897A2_D0007.tif" /></maths><maths id="math0008" num=""><math display="block"><msub><mi mathvariant="normal">f</mi><mi mathvariant="normal">x</mi></msub><mo mathvariant="normal">=</mo><msub><mi mathvariant="normal">F</mi><mi mathvariant="normal">m</mi></msub><mo mathvariant="normal">-</mo><msub><mi mathvariant="normal">F</mi><mi mathvariant="normal">n</mi></msub><mo mathvariant="normal">-</mo><msub><mi mathvariant="normal">f</mi><mi mathvariant="normal">n</mi></msub></math><img file="EP2000897A2_D0008.tif" /></maths>

0040If the number of records and the number of file marks are computed in accordance with the above expressions by the computation section 150, the communication section (sending section) 110 sends the number information to the host computer 400. In the tape reader 100 according to one embodiment of the invention, the communication section (sending section) 110 directly sends the computed number of records and the computed number of files marks, together with the error information, to the host computer 400. In this case, the host computer 400 needs to specify the next data reading position based on the computed number of records and the computed number of file marks to continue reading the data.

0041Thus, the tape reader 100 according to another embodiment of the invention further comprises a generation section 160 for generating the dummy records for the computed number of records and the file marks for the computed number of file marks not to interrupt reading the data. And the communication section (sending section) 110 sends the generated dummy records and dummy file marks as the number information to the host computer 400. In this case, the generation section 160 can generate the dummy records with the length of read data designated in an instruction sent from the host computer 400 to the tape reader 100 as the length of dummy record. Specifically, the generation section 160 decides the length of dummy record based on FixedBit, Suppress Incorrect Length Indicator (SILI) Bit and TransferLength included in the Read command sent from the host computer 400 and BlockLength included in BlockDescriptor which is sent together with a ModeSelect command ahead of the Read command from the host computer 400.

0042Before describing a specific method for deciding the length of dummy record, a SCSI command will be firstly described below. The ModeSelect command is the command for sending the configuration data to the tape drive before instructing the tape drive to read or write. In the ModeData sent together with the ModeSelect command, a BlockDescriptor (BD) field of 8 Bytes is defined, and the BlockLength as defined in 5 to 7 Bytes of the BD field is used as the length of logical block in a series of reading operations, for example.

0043Next, the Read command will be described below. In the Read command, a Suppress Incorrect Length Indicator (SIL) field is defined in Byte1 Bit1, a Fixed field is defined in Byte1 Bit0, and a TransferLength field is defined in 2 Byte to 4 Byte. When 1 is set in the Fixed field, the TransferLength field is not 0, and SILI is set to 0, then the block having the length of BlockLength is read and returned to the host computer. At this time, the value of the TransferLength field indicates the number of blocks to be returned to the host computer. On the other hand, when SILI is set to 1, the tape drive returns a CheckCondition status to the host computer.

0044The CheckCondition status is returned in response to the SCSI command received by the tape drive, when it is required to convey an error or warning to the host computer. Since the CheckCondition status only conveys that there is a problem, the tape drive further returns the SenseData to notify the details of error. In the SenseData, a SenseKey field is defined in 2 Byte 0 to 3 Bits, and the content of error is indicated by the SenseKey field. This SenseData can be returned to the host computer at the same time with the CheckCondition in the serial SCSI such as a FiberChannel. On the other hand, in the parallel SCSI, the SenseData can be returned in response to a Request Sense command issued from the host computer to inform the details of error.

0045For the Read command, when the Fixed field is set to 0, and the TransferLength field is not 0, the single block having the length of TransferLength is read. If the SILI field is set to 0, the CheckCondition status may need to be reported in accordance with the length of data that can be read or the value of BlockLength.

0046In the tape reader 100 according to one embodiment of the invention, the length of dummy record to be returned to the host computer 400 is estimated and decided using the SCSI command. That is, in the Read command, when 1 is set in the Fixed field, the generation section 160 has the length of BlockLength as the length of dummy record. Also, when 0 is set in the Fixed field, the generation section 160 has the length of TransferLength as the length of dummy record. However, when 0 is set in the Fixed field and 1 is set in the SILI field, the generation section 160 has the length of BlockLength as the length of dummy record as far as the BlockLength is not 0.

0047Herein, the estimation of record length may not rely on the tape reader 100 by newly defining a 0 byte block mode in which the length of dummy record is returned as zero. In this case, since the number of records and the number of file marks included in a part where the error occurs is sent to the host computer 400 in accordance with the normal data reading procedure, the reading of data is not interrupted, because the computed number of records and the computed number of file marks are not simply returned to the host computer 400. The 0 byte block mode can be set in the tape reader 100, using a ModeSelect command, for example.

0048The communication section (sending section) 110 sends the dummy records and file marks generated by the generation section 160, together with the dummy information indicating that the data is dummy, to the host computer 400. As one example, the communication section (sending section) 110 sends the CheckCondition and the SenseData to the host computer 400.

0049<figref idref="f0002">Figure 6</figref> shows one example of the functional configuration of the host computer 400 according to this embodiment. The host computer 400 comprises a sending section 410, a receiving section 420, and a judgment section 430. The sending section 410 sends a command for reading such as the ModeSelect command or Read command to the tape reader 100. The receiving section 420 receives the number information from the tape reader 100. And the judgment section 430 judges the tape reading position based on the number information. In the preferred embodiment, the receiving section 420 receives the dummy records and file marks as the number information together with the dummy information from the tape reader 100. And the judgment section 430 judges whether or not the records and file marks received as the number information are dummy based on the dummy information. As described above, the tape reader 100 returns the CheckCondition and the SenseData to the host computer 400, as one example. The host computer 400 knows that there occurs some problem because of receiving the CheckCondition, and investigates the SenseData to know the error content. And the host computer 400 judges that the received records and file marks are dummy if the MediumError is set in the SenseKey as dummy information.

0050In the above way, with the tape reader 100 according to the embodiment of the invention, if the read error occurs, the number of records and the number of file marks included in the part where the error occurs are computed and conveyed to the host computer 400, whereby the host computer 400 that manages the reading position of data based on the received number of records and the received number of file marks can correctly recognize and manage the data position. However, if the read error occurs, it may be desired to once interrupt the reading in some cases to investigate the cause of error minutely. Thus, preparing two modes, a normal operation mode of only returning the read error when the read error occurs and a rescue mode of returning the number of records and the number of file marks included in the part where the read error occurs when the read error occurs, the host computer 400 may select the mode and set it to the tape reader 100. The mode can be set using the ModeSelect command, for example.

0051Referring to the flowcharts of <figref idref="f0003 f0004">Figures 7 to 9</figref>, the operation of the tape reader 100 according to the embodiment will be described below. At step 100 of <figref idref="f0003">Figure 7</figref>, the communication section (receiving section) 110 receives the data reading command, or the Read command, from the host computer 400. The reading section 130 reads data in DS units from the tape medium 200 in accordance with the Read command under the control of the reading control section 140 (S110). If an error occurs in reading the data (S120: YES), the process advances to step 130, where an error process is performed. On the other hand, if the DS is read without problem (S120: NO), the reading section 130 stores the read DS in the buffer 120 (S140). At the time when plural DSs are stored in the buffer 120, the communication section (sending section) 110 sends the plural DSs to the host computer 400 (S150). And the process is ended.

0052Referring to a flowchart of <figref idref="f0003">Figure 8</figref>, the error process at step 130 will be described below. If an error occurs in reading the data, the reading control section 140 controls the reading section 130 to skip the DS where the error occurs, and read the next readable DS immediately after the DS where the error occurs (S200). The reading section 130 stores the read DS next to the DS where the error occurs in the buffer 120. The computation section 150 retrieves the information on the records and file marks included in the DS preceding to the DS where the error occurs and the information on the records and file marks included in the DS next to the DS where the error occurs from the DSIT of the DS preceding to the DS where the error occurs stored in the buffer 120 and the DSIT of the DS next to the DS where the error occurs, and computes the number of records and the number of file marks included in the DS (possibly plural DSs) where the error occurs (S210). The specific computation method has been described above, and is not described here to avoid repetition. Thereafter, the generation section 160 generates the dummy records for the computed number of records and the file marks for the computed number of file marks, and the communication section (sending section) 110 sends the generated dummy records and file marks together with the dummy information to the host computer 400 (S220).

0053Referring to a flowchart of <figref idref="f0004">Figure 9</figref>, the process at step 220 will be described below. It is assumed that the number of records included in the DS where the error occurs is r_x and the number of file marks is f_x. The process starts at step 300. First of all, the generation section 160 substitutes r_x and f_x as the initial values into the variables x and f. At step 310, the generation section 160 checks the values of the variables x and f, in which if both are 0, the process is ended (S310: YES). If the answer is NO at step 310, the generation section 160 further checks whether or not the value of the variable r is greater than 0. When the judgment at steps 310 and 320 is made for the first time, the process advances to the next step 330 to decide the length of dummy record, because the value of the variable r is greater than 0.

0054If the value of the variable r is greater than 0 (S320: YES), the generation section 160 checks the Fixed field of the Read command (S330). In the tape reader 100 according to the embodiment of the invention, if the Fixed field is not set to 1, the generation section 160 does not directly have the value of TransferLength in the Read command as the length of dummy record, but has the value of BlockLength as the length of dummy record when the SILI is set to 1 by checking the SILI field of the Read command, unless the value of BlockLength designated beforehand from the host computer 400 is 0, as described above. Thus, if the answer is NO at step 330, the generation section 160 checks the SILI of the Read command (S340). If the SILI is set to 1 (S340: YES), the generation section 160 further checks the value of BlockLength (S350), in which if not 0 (S350: NO), the value of BlockLength is made the length of dummy record (S360).

0055If the SILI is not set to 1 (S340: NO), or if the SILI is set to 1 but the value of BlockLength is 0 (S350: YES), the process advances to step 370, where the generation section 160 judges whether or not the 0 byte block mode of returning the length of dummy record as 0 is set. If the 0 byte block mode is not set (S370: NO), the generation section 160 makes the value of TransferLength in the Read command the length of dummy record (S380). If the 0 byte block mode is set (S370: YES), the generation section 160 makes the length of dummy record 0. And the process advances from step 360, 380 or 390 to step 400, where the generation section 160 decrements the value of variable r by 1. Also, at step 450, the communication section (sending section) 110 returns the CheckCondition for informing the read error to the host computer 400. Further, the communication section (sending section) 110 returns the SenseData with MediumError set in the SenseKey to allow the host computer 400 to identify that the sent record is the dummy record having the estimated length (S450). Thereafter, the process returns to step 310 to generate the computed number r_x of dummy records repetitively.

0056On the other hand, if the Fixed field is set to 1 (S330: YES), the generation section 160 makes the value of BlockLength the length of dummy record (S410). And at step 420, the value of variable r is decremented by 1, and the generation section 160 judges whether or not the record is last record (S430). This is because if the Fixed field is set to 1, the reading is continuously performed, whereby the dummy information is returned only after the last record. Thus, if the record is not last record (S430: NO), the process returns to step 310 to generate the dummy record consecutively. If the record is last record (S430: YES), the process advances to step 450, the dummy information is returned to the host computer 400, as described above.

0057Returning to step 320, if the variable r is smaller than or equal to 0 (S320: NO), the communication section (sending section) 110 sends the file mark to the host computer 400 this time (S460). Specifically, the communication section (sending section) 110 returns the CheckCondition for informing the read error to the host computer 400, and at this time, the generation section 160 sets up a bit of the file mark in the SenseData. Also, to allow the host computer 400 to identify that the sent file mark is dummy, the communication section (sending section) 110 returns the SenseData with MediumError set in the SenseKey. Thereafter, the process returns to step 310, to return the computed number f_x of dummy file marks repetitively.

0058Referring to a flowchart of <figref idref="f0005">Figure 10</figref>, the operation of the host computer 400 according to the embodiment will be described below. At step 500 of <figref idref="f0005">Figure 10</figref>, the sending section 410 of the host computer 400 sends the Read command to the tape reader 100. At step 510, the receiving section 420 receives the records and file marks as a response to the Read command from the tape reader 100. At this time, the judgment section 430 judges whether or not the CheckCondition and SenseData are sent following the records and file marks (S520). If the CheckCondition is sent (S520: YES), the judgment section 430 checks whether or not the MediumError is set in the SenseKey field of the SenseData to investigate the content of error. If the MediumError is set, the judgment section 430 judges that the received records and file marks are dummy data (S530), and the process is ended. If it is judged that the received records and file marks are dummy, the host computer 400 may simply cancel the dummy records and file marks, or may perform a process for recovering or complementing the lost data corresponding to the dummy records and file marks.

0059<figref idref="f0006">Figure 11</figref> on the left side shows one example of the hardware configuration of the tape reader 100 according to the embodiment. The tape reader 100 comprises a tape drive 630, a CPU 600, RAM 610, ROM 620 and a communication interface 640, which are interconnected via a bus. The tape drive 630 reads data from the tape medium 200, and provides it to the RAM 610. The ROM 620 stores a boot program that the CPU 600 executes at the time of starting the tape reader 100 and a program for operating the tape reader 100 after start-up. And the CPU 600 executes these programs using the RAM 610. A program for the tape reader for processing the data read error from the tape medium according to the invention is also stored in the ROM 620, and executed using the RAM 610 by the CPU 600. The program for the tape reader enables the tape reader 100 to function as the data reading section 130, the reading control section 140, the a computation section 150, the generation section 160 and the communication section 110. The explanation of the specific function and operation, which are the same as described using <figref idref="f0002">Figures 4</figref>, <figref idref="f0003">7</figref> and <figref idref="f0004">9</figref>, is omitted.

0060The program provided to the tape reader 100 is read from the tape medium 200 by the tape drive 630, and installed in the tape reader 100. Alternatively, the communication interface 640 may acquire the program from the host computer 400 via an input/output device such as a serial port or a network, and install it in the tape reader 100. The program provided to the tape reader 100 is stored in the tape medium 200, a flexible disk, an optical recording medium such as CD-ROM, DVD or PD, an optical magnetic storage medium such as MD, or a semiconductor memory such as IC card, and provided by the user.

0061<figref idref="f0006">Figure 11</figref> on the right side shows one example of the hardware configuration of the host computer 400 according to the embodiment. The host computer 400 comprises a CPU peripheral section having a CPU 700 and a RAM 720 that are interconnected by a host controller 710, an input/output section having a communication interface 760, a hard disk drive 740, and a CD-ROM drive 750 that are connected to the host controller 710 by an input/output controller 730, and a legacy input/output section having a super I/O controller 770 connected to the input/output controller 730, and a flexible disk drive 780, a flash ROM 790 and a keyboard mouse controller 800 connected to the super I/O controller 770.

0062The host controller 710 connects the CPU 700 that gains access to the RAM 720 at high transfer rate to the RAM 720. The CPU 700 operates to control each section, based on a program stored in the hard disk. A program for the host computer for processing the data read error from the tape medium according to the invention is stored in the hard disk and executed using the RAM 720 by the CPU 700. The program for the host computer enables the host computer 400 to function as the sending section 410, the receiving section 420, and the judgment section 430. The explanation of the specific function and operation, which are the same as described using <figref idref="f0002">Figures 5</figref> and <figref idref="f0005">10</figref>, is omitted.

0063The input/output controller 730 connects the communication interface 760, the hard disk drive 740 and the CD-ROM drive 750, which are relatively high speed input/output devices, to the host controller 710. The communication interface 760 communicates with an external device such as the tape reader 100 via the network. The CD-ROM drive 750 reads the program or data from the CD-ROM, and provides it via the communication interface 760 to the tape reader 100.

0064Also, the relatively low speed input/output devices such as the flexible disk drive 780 and the keyboard mouse controller 800 and the flash ROM 790 are connected to the input/output controller 730. The flash ROM 790 stores a boot program executed by the CPU 700 at the time of starting the host computer 400 and a program dependent on the hardware of the host computer 400. The flexible disk drive 780 reads a program or data from a flexible disk, and provides it via the RAM 720 to the super I/O controller 770. The super I/O controller 770 connects the flexible disk and various input/output devices via a parallel port, a serial port, a keyboard port or a mouse port, for example.

0065Though the invention has been described above using the embodiments, the technical range of the invention is not limited to the range as described in the above embodiments. For example, in the above embodiment, the number of records and the number of file marks included in the part of the tape medium 200 where the error occurs was computed by the computation section 150 of the tape reader 100. However, the sending section 110 of the tape reader 100 may retrieve the first information on the records and the boundary marks indicating the boundary of record block included in the data unit preceding to the data unit where the error occurs that is read immediately before the error occurs, and the second information on the records and boundary marks included in the data unit next to the data unit where the error occurs from the buffer 120 storing the data unit read by the reading section 130, and send them to the host computer 400. And the judgment section 430 of the host computer 400 may judge the reading position of data by computing the number of records and the number of boundary marks included in the data unit where the error occurs, based on the first information and the second information. It will be apparent to a person skilled in the art that various variations or improvements may be made to the above embodiments. Accordingly, the embodiments with such variations or improvements may be encompassed within the technical range of the invention.

[Brief description of the drawings]

0066<ul id="ul0001" list-style="none"><li><figref idref="f0001">Figure 1</figref> shows one example of the configuration of a system 10 for processing a data read error from a tape medium according to one embodiment of the present invention;</li><li><figref idref="f0001">Figure 2(a)</figref> shows one example of the organization of a recording area conforming to the LTO standards in the tape medium 200 according to this embodiment, and <figref idref="f0001">Figure 2(b)</figref> shows the organization of a dataset in an LTO data format;</li><li><figref idref="f0001">Figure 3(a)</figref> shows a state where data is firstly written into the tape medium 200 conforming to the LTO standards, and <figref idref="f0001">Figure 3(b)</figref> shows a state after data is overwritten on the tape medium 200 as shown in <figref idref="f0001">Figure 3(a)</figref>;</li><li><figref idref="f0002">Figure 4</figref> shows one example of the functional configuration of a tape reader 100 according to this embodiment;</li><li><figref idref="f0002">Figure 5</figref> shows a state where a read error occurs in the tape medium 200 conforming to the LTO standards;</li><li><figref idref="f0002">Figure 6</figref> shows one example of the functional configuration of a host computer 400 according to this embodiment;</li><li><figref idref="f0003">Figure 7</figref> is a flowchart showing the flow of a process for reading data in response to a Read command in the tape reader 100 according to this embodiment;</li><li><figref idref="f0003">Figure 8</figref> is a flowchart showing the flow of an error process in the tape reader 100 according to this embodiment;</li><li><figref idref="f0004">Figure 9</figref> is a flowchart showing the flow of a process for generating dummy record and sending dummy information in the tape reader 100 according to this embodiment;</li><li><figref idref="f0005">Figure 10</figref> is a flowchart showing the flow of a read error process in the host computer 400 according to this embodiment; and</li><li><figref idref="f0006">Figure 11</figref> shows one example of the hardware configuration of the tape reader 100 and the host computer 400 according to this embodiment.</li></ul>