Abstract:
A re-recording/re-reproducing device cleans both the magnetic tape and head of dregs which cause errors in writing and reading. A magnetic head records and reproduces input digital data to and from a magnetic tape at a normal speed. When an error in writing or reading the input digital data is detected, the tape is moved to a position where the error is detected and the magnetic head re-records/re-reproduces the input digital data to and from the magnetic tape, but does so at a speed higher than the normal speed of recording/reproducing, resulting in the removal of the dregs from the magnetic tape and head.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a magnetic tape recording/reproducing apparatus for recording and reproducing digital data supplied from for example an external computer. 
     2. Description of the Related Art 
     A magnetic tape recording/reproducing apparatus that is used as an external storage unit for a computer is known. In this case, a drive unit that loads a digital cassette tape is connected to a host computer through an interface. As an example of the data recorder, a helical scan type recorder that records digital data on a cassette tape with a rotating head is known. 
     Such a data recorder is connected to for example a SCSI (Small Computer Interface System) standard interface. Since the host computer recognizes the interface unit as a data recorder, it has a function for generating a file format on a tape and sending/receiving data to/from the tape (this function is referred to as formatter). The interface unit has a buffer memory that temporarily stores data transmitted between the host computer and the data recorder. 
     When an uncorrected error that cannot be corrected by signal processes such as a data recording process and a signal reproducing process takes place, with data temporarily stored in a buffer memory, write retry/read retry operations can be performed for the magnetic tape. For example, when data is read from the buffer memory and recorded on the tape for every buffer unit, the write retry operation is performed at an area (including a non-record area) followed by an invalid area in which data has not been recorded. When data is reproduced, the read retry operation is performed from an area in which data has not been reproduced. 
     As described above, the write retry operation and the read retry operation for data are certainly effective if a magnetic tape is partially damaged. However, in the case that dregs adhere on the tape or that magnetic particles of the magnetic tape adhere on a recording head or a reproduction head (this situation is referred to as head clogging), even if the different heads are used, since the tape with dregs is used, the write retry operation and the read retry operation for data cannot be performed. Alternatively, even if the different tape is used or the record area on the tape is changed, since the heads with dregs are used, the write retry operation and the read retry operation for the data cannot be performed. 
     OBJECT AND SUMMARY OF THE INVENTION 
     The present invention is made from the above-described point of view. An object of the present invention is to provide a magnetic tape recording/reproducing apparatus for performing a retry operation so as to record/reproduce data to/from a magnetic tape even if data cannot be recorded or reproduced due to head clogging or the like. 
     The present invention is a recording apparatus for a magnetic tape, comprising a recording means having a magnetic head for recording input digital data on the magnetic tape at a normal speed, a reproducing means for reproducing data recorded by the recording means, a driving means for driving the magnetic tape, a detecting means for detecting an error in data reproduced by the reproducing means and outputting an error detection signal representing the detected result, and a control means for controlling the driving means and the recording means corresponding to the error detection signal so that the input digital data corresponding to the detected error is re-recorded on the magnetic tape after the magnetic tape is moved to a re-recording start position corresponding to a tape position at which the error is detected at a speed higher than the normal speed so as to remove dregs from the magnetic head and the magnetic head. 
     When data with an uncorrected error is detected by a system controller  31 , the system controller  31  sends a control signal to a motor drive circuit  49 . With the control signal, a motor  50  is driven and thereby a magnetic tape  91  is moved from a first position to a second position. Thereafter, the magnetic tape  91  is moved to the first position once again. At the first position, a write retry operation or a read retry operation is performed. 
     These and other objects, features and advantages of the present invention will become more apparent in light of the following detailed description of a best mode embodiment thereof, as illustrated in the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a front view showing a magnetic tape recording/reproducing apparatus according to the present invention; 
     FIG. 2 is a rear view showing the magnetic tape recording/reproducing apparatus according to the present invention; 
     FIG. 3 is a schematic diagram showing an example of the application of the magnetic tape recording/reproducing apparatus according to the present invention; 
     FIG. 4 is a schematic diagram showing a structure of heads of a digital information recorder; 
     FIG. 5 is a schematic diagram showing a track pattern of a cassette tape; 
     FIG. 6 is a block diagram showing a system structure of the magnetic tape recording/reproducing apparatus; 
     FIG. 7 is a detailed block diagram showing the system structure of the magnetic tape recording/reproducing apparatus; 
     FIG. 8 is a schematic diagram showing a tape format of the cassette tape; 
     FIGS. 9A,  9 B and  9 C are schematic diagrams showing VSIT and DIT formats of the cassette tape; 
     FIG. 10 is a schematic diagram for explaining a bad spot table; 
     FIG. 11 is a schematic diagram showing a logical format of the cassette tape; and 
     FIG. 12 is a schematic diagram showing a record data area of the cassette tape. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Next, with reference to the accompanying drawings, a data recorder according to the present invention will be described. The data recorder records/reproduces digital data to/from a cassette tape with a rotating head. FIG. 1 is a front view showing the data recorder. FIG. 2 is a rear view of the data recorder. 
     As shown in FIGS. 1 and 2, the data recorder is composed of two units that are an upper unit and a lower unit. The lower unit is literally disposed below the upper unit. The lower unit is a tape drive controller  1 . The upper unit is a digital information recorder  2 . The tape drive controller  1  has a front panel that includes a button  3  and a plurality of light emitting diodes  4 . The button  3  is used to perform the loading/unloading processes for a cassette tape. The light emitting diodes  4  represent whether or not a cassette tape has been loaded, whether or not the power has been turned on, and so forth. In addition, the digital information recorder  2  has a detachable panel  6 . Inside the detachable panel  6 , other operation buttons are disposed. The digital information recorder  2  has a front panel with a cassette tape loading/unloading opening  5 . 
     As shown in FIG. 2, on the rear panels of the tape drive controller  1  and the digital information recorder  2 , a plurality of connectors are disposed. On the rear panel of the lower tape drive controller  1 , a data input/output connector  11 , a control connector  12 , an RS232C connector  13 , two SCSI connectors  14  and  14   b , an AC power input connector  15 , and a DC power output connector  16  are disposed. 
     On the rear panel of the digital information recorder  2 , a data input/output connector  21 , a control connector  22 , and an RS232C connector  23  are disposed. By connecting a dedicated cable to the DC power output connector  16  of the tape drive controller  1 , power is supplied to the digital information recorder  2 . The data input/output connectors  11  and  21  are connected with a dedicated cable. Data is sent and received between the controller  1  and the recorder  2 . The control connectors  12  and  22  are connected with a dedicated cable. Thus, control signals are exchanged between the controller  1  and the recorder  2 . The RS232C connectors  13  and  23  are used for diagnosis purposes. 
     As shown in FIG. 3, when a host computer  20  is connected to the data recorder, the SCSI connectors  14   a  and  14   b  are used. When the host computer  20  sends for example a read command to the data recorder, it outputs data to the host computer  20 . 
     The digital information recorder  2  records/reproduces data to/from a cassette tape with rotating heads. (In the following description, the rotating heads may be treated as a single head for convenience.) FIG. 4 shows the arrangement of the heads used in the recorder  2 . Four record heads Ra, Rb, Rc, and Rd and four reproduction (playback) heads Pa, Pb, Pc, and Pd are disposed on a drum  25  that rotates at a predetermined speed in the direction shown in FIG.  4 . 
     The heads Ra and Rb are adjacently disposed. This relation applies to pairs of heads Rc and Rd, heads Pa and Pb, and heads Pc and Pd. The extended directions of each pair of heads are different from each other. The extended directions are referred to as azimuths. Referring to FIG. 4, the heads Ra and Rc are disposed at an interval of 180° and have a first azimuth. The heads Rb and Rd are disposed at an interval of 180° and have a second azimuth. The heads Pa and Pc have the first azimuth. The heads Pb and Pd have the second azimuth. With the different azimuths, cross talks can be prevented between adjacent tracks. Each of the adjacent heads is integrally composed as one head. The integrally composed head is referred to as a double-azimuth head. 
     A tape (for example, {fraction (1/2 )} inch wide) that is led out of the cassette is helically wound around the periphery of the drum  25  for an angle range of 180° or greater. The tape is supplied at a predetermined speed. Thus, when a signal is recorded to the tape, in the first half period of one rotation of the drum  25 , the heads Ra and Rb scan the tape. In the second half period, the heads Rc and Rd scan the tape. When a signal is reproduced from the tape, in the first period, the heads Pa and Pb scan the tape. In the second period, the heads Pc and Pd scan the tape. 
     FIG. 5 shows a track pattern on the tape of the digital information recorder  2 . Longitudinal tracks are disposed in the width direction of the tape. Helical tracks are disposed between the longitudinal tracks. A control signal is recorded on an upper longitudinal track  26 . A time code is recorded on a lower longitudinal track  27 . The time code represents the position in the longitudinal direction of the tape. For example, the time code is an SMPTE time code. Whenever the drum  25  is rotated, the head Ra and Rb form two helical tracks Ta and Tb at the same time. Thereafter, the heads Ra and Rb form two helical tracks Tc and Td at the same time. On each helical track, a first half portion and a second half portion are separately formed. Between the first half portion and the second half portion of each helical track, a record area  28  is disposed. The record area  28  is used to record a tracking pilot signal. 
     The SMPTE time code was developed for a video signal for use with a VCR or the like. The minimum unit of the SMPTE time code is a frame ({fraction (1/30)} second). As will be described later, in the data recorder, data that can be recorded on the four tracks Ta to Td shown in FIG. 5 is defined as a logical data unit. When  16  tracks accord with one frame of a video signal, a subdigit (values 0, 1, 2, and 3) lower than the digit of the frame of the time code is defined. This time code is also referred as ID. Since the SMPTE time code has a user data area, such a modification can be performed. 
     FIG. 6 is an outlined block diagram showing a system structure of the tape drive controller  1  and the digital information recorder  2 . The controller  1  has a system controller  31 . The system controller  31  has the following functions. 
     Managing a SCSI controller  32 , 
     Managing a buffer memory  33 , 
     Managing files/tables, 
     Writing/reading data and controlling retries, 
     Controlling the digital information recorder  2 , and 
     performing self diagnosis. 
     The data recorder is connected to the host computer through the SCSI controller  32  of the digital information recorder  2 . Data that is read from the buffer memory  33  is supplied to a C2 encoder  35  through the drive controller  34 . Data that is received from the C2 encoder  35  is supplied to a C1 encoder  37  through a track interleave circuit  36 . 
     The C2 encoder  35  and the C1 encoder perform an error correction encoding process for record data with a product code. The track interleave circuit  36  controls the distribution of data to tracks on the tape so as to improve the error correction performance in the recording/reproducing processes. 
     When data is recorded on the tape, it is recorded as SYNC blocks separated by a synchronous signal. In this case, the track interleave circuit  36  adds a block synchronous signal to the output signal of the C2 encoder  35 . The C1 encoder  37  generates a C1 parity. Thereafter, data is randomized and words are interleaved in a plurality of SYNC blocks. 
     Digital data that is output from the C1 encoder  37  is supplied to the digital information recorder  2 . The digital information recorder  2  encodes digital data received from a channel code encoder  38 . The resultant record data is output to the record heads Ra to Rd through an RF amplifier  39 . The heads Ra to Rd record the record data on the tape. The RF amplifier  39  performs a process corresponding to partial response class  4  (PR (1, 0, −1)). 
     Data reproduced from the tape by the reproduction heads Pa to Pd is supplied to a channel code decoder  42  through an RF amplifier  41 . The RF amplifier  41  includes a reproducing amplifier, an equalizer, and a Viterbi decoder. The output data of the channel code decoder  42  is supplied to the tape drive controller  1 . The output data of the channel code decoder  42  is supplied to a C1 decoder  43 . 
     The C1 decoder  43  is connected to a track deinterleave circuit  44 . The track deinterleave circuit  44  is connected to a C2 decoder  45 . The C1 decoder  43 , the track deinterleave circuit  44 , and the C2 decoder  45  perform the reverse processes of the C1 encoder  37 , the track interleave circuit  36 , and the C2 encoder  35 , respectively. The C2 decoder  45  supplies the reproduction (read) data to the buffer memory  33  through the drive controller  34 . In addition, the C2 decoder  45  determines whether or not the reproduction (read) data is different from the record data. If they are different from each other, the C2 decoder  45  supplies an uncorrected error generation signal to the system controller  31 . 
     The digital information recorder  2  has a system controller  46 . In addition, the digital information recorder  2  has a fixed head  47  for the longitudinal tracks on the tape. The head  47  is connected to the system controller  46 . The head  47  records/reproduces a control signal and a time code. The system controller  46  is connected to the system controller  31  of the tape drive controller  1  through a bidirectional bus. The system controller  31  determines whether or not data that is recorded or reproduced has an uncorrected error. 
     A mechanism controller  48  is connected to the system controller  46 . The mechanism controller  48  includes a servo circuit that drives a motor  50  through a motor drive circuit  49 . The system controller  46  has for example two CPUs. The system controller  46  communicates with the tape drive controller  1 , controls recording/reproducing of a time code, controls recording/reproducing timings, and so forth using the CPUs. 
     The mechanism controller  48  has for example two CPUs. The mechanism controller  48  controls a mechanical system of the digital information recorder  2  with the CPUs. In particular, the mechanical controller  48  controls the rotation of the head and tape system, the tape speed, the tracking operation, loading/unloading processes of the cassette tape, and the tape tension. The motor  50  includes a drum motor, a capstan motor, a reel motor, a cassette mounting motor, a loading motor, and so forth. 
     The digital information recorder  2  has a DC-DC converting circuit  52  that receives a DC voltage from a power supply unit  51  of the tape drive controller  1 . The digital information recorder  2  also has position sensors (such as a tape end detecting sensor), a time code generating/reading circuit, and so forth (that are not shown). 
     FIG. 7 is a block diagram showing a system structure of the tape drive controller  1 . Reference numeral  61  is a main CPU. Reference numeral  70  is a two-port RAM. Reference numeral  80  is a bank memory. Reference numeral  81  is a sub CPU. The main CPU  61  is a CPU that manages the entire system. In association with the main CPU  61 , a CPU bus  62  is disposed. Each structural portion of the tape drive controller  1  is connected to the CPU bus  62 . In other words, a ROM (flash ROM)  63 , PIOs (parallel I/Os)  64  and  65 , a control panel  66 , an LCD  67 , a timer  68 , an RS232C interface  69 , a two-port RAM  70 , and a RAM  71  are connected to the CPU bus  62 . 
     The PIO  65  is connected to a button on the front panel. The LCD  67  is a display unit that displays the operation state of the drive so that the user can know it. The RS232C interface  69  is connected to a serial terminal. The RAM  71  is a work RAM for use with firmware. The RAM  71  has a down-load area of programs and temporarily stores header information (VSIT (Volume Set Information Table/DIT (Directory Information Table)). 
     An IM bus  74  is connected to the CPU bus  62  through a unidirectional controlling device  73 . An SRAM  72 , a bank memory  80 , and an SCSI controller  75  are connected to the IM bus  74 . The host computer is connected to the SCSI controller  75  through a bus  76 . The S-RAM  72  is a back-up RAM with a condenser. The SRAM  72  is used for a script memory (for storing a control program for the SCSI controller). In addition, the S-RAM  72  is used for a logger memory for representing a real operation state of the system. Since this memory is backed up with the condenser, after the power of the system is turned off, the memory can hold data for around two days. 
     The two-port RAM  70  stores five types of packets for communicating information between the two CPUs  61  and  81 . The five types of packets are (1) a command transmission packet that is used when the main CPU  61  requests the sub CPU  81  to perform an operation, (2) an end status reception packet that is used when the end status of the operation of the sub CPU  81  is sent corresponding to a command requested by the main CPU  61 , (3) a command status that is a flag representing the progress status of a command, (4) a drive management status table used to inform the main CPU  61  of the status of the drive (this table is rewritten by the sub CPU  81  at predetermined periods), and (5) a data send/receive packet that is a buffer used when the firmware on the CPU  81  side is downloaded from the CPU  61  side through the SCSI bus  71  or when a diagnosis on the CPU  81  side is activated with the RS232C interface  69  of the main CPU  61 . The bank memory  80  is a buffer memory for data. 
     The sub CPU  81  is a CPU that controls the digital information recorder  2 . In association with the sub CPU  81 , a CPU bus  82  is disposed. The CPU bus  82  is connected to a ROM (flash ROM)  83 , a RAM (work RAM)  84 , a timer  85 , an RS232C interface  86 , an RS422 interface  87 , a PIO (Parallel I/O)  88 , and a DMA controller  89 . In addition, the CPU bus  82  is connected to the two-port RAM  70  and the bank memory  80 . 
     The bank memory  80  stores data that is written to the tape or data that is read from the tape  91 . The DMA (Direct Memory Access) controller  89  stores data to the bank memory  80 . The RS232C interface  86  is used for a self diagnosis. The RS422 interface  87  is a communication means with the digital information recorder  2 . 
     Next, the record format of digital data will be described. 
     FIG. 8 shows the layout of the entire tape (in a cassette, for example). The entire tape is referred to as physical volume. The tape has a leader tape. Between the PBOT (Physical Beginning of Tape) and the PEOT (Physical End of Tape) of a physical tape, a recordable area is between the LBOT (Logical Beginning of Tape) and the LEOT (Logical End of Tape). The recordable area is defined because the tape tends to be damaged at the beginning and end of the tape and thereby the error rates thereof are high. For example, the invalid area between the PBOT and the LBOT is defined 7.7±0.5 m. In addition, the invalid area between the PEOT and LEOT is defined 10 m or greater. 
     One physical volume has a plurality of logical volumes (referred to as partitions). 
     To manage one or more logical volumes, a VSIT (Volume Set Information Table) is recorded at the beginning of the record area. The VSIT includes the number of volumes recorded on the tape and position information of the logical volumes on the tape. The position information includes start physical IDs and end physical IDs of DITs (Directory Information Tables) of up to 1024 logical volumes. 
     The position at the beginning of the VSIT is defined as the position of 0-ID. An ID (Identification) is an address corresponding to the position of every set of four tracks on the tape. IDs are simply incrementally assigned from the VSIT area to the DIT area of the last volume. The length of one VSIT is 1-ID. 
     A logical volume is composed of a DIT (Directory Information Table), an UIT, and a user data area. The DIT has information for managing a file in the logical volume. The length of one DIT is 40-IDs. The UIT is optional. The UIT is user information for managing a file. 
     In FIG. 8, hatched areas are run-up areas. With run-up areas, data tracks are servo-locked. Dotted areas are position tolerance areas. With the position tolerance areas, when the VSIT and the DIT are updated, valid data can be prevented from being erased. 
     As shown in FIG. 9A, the VSIT is repeatedly recorded ten times so as to improve the reliability of data. Thus, the VSIT area is composed of 10 track sets (=10-IDs). The VSIT area is followed by a retry area composed of 90 track sets or more. 
     As shown in FIG. 9B, the DIT is repeatedly recorded seven times. As shown in FIG. 9C, the DIT is composed of six tables. The six tables are a VIT (Volume Information Table), a BST (Bad Spot Table), an LIDT (Logical Information Table), an FIT (File Information Table), a UT (Update Table), and a UIT (User Information Table) disposed in the order. Each of the VIT, the BST, the LIDT, and the UT has the length of 1-ID. The FIT has the length of 20-IDs. The remaining area for 16-IDs is reserved. 
     Next, each table of the DIT will be described. The ID address of the VIT is a physical ID at the beginning of volumes written in the VSIT. The logical ID of the VIT is equivalent to the physical ID at the beginning of the volumes written in the VSIT. The VIT includes a volume label and volume information such as a start physical ID of the first data block in the physical volume and the last physical ID thereof. 
     The ID address of the BST is the physical ID of the VIT plus 1, whereas the logical ID thereof is the logical ID of the VIT plus 1. The BST has position information of logically invalid data. The logically invalid data is data that is treated invalid because of presence of the same track set ID. For example, as shown in FIG. 10, a hatched area A is logically invalid data. A write retry operation and a write operation associated therewith cause logically invalid data. When a write operation is performed, if an error takes place, a write retry is automatically performed and an error location thereof is output. The error location is stored in the BST. When a read operation is performed, the BST represents an invalid area. The logically invalid data is also referred to as bad spot. The BST can manage top physical IDs and last physical IDs of up to 14592 bad spots. 
     The ID address of the LIDT is the physical ID of the VIT plus 2, whereas the logical ID thereof is the logical ID of the VIT plus 2. The LIDT is a data table for a high speed block space and a locating operation. In other words, the LIDT includes logical IDs and physical IDs of pointers 1 to 29, file numbers, and the first block number of the ID data in the block management table. 
     The ID address of the FIT is the physical ID of the VIT plus 3, whereas the logical ID thereof is the logical ID of the VIT plus 3. The FIT is composed of a plurality of pairs of two types of data corresponding to tape marks. The tape marks are file delimiter codes. The N-th data pair accords with an Nth tape mark counted from the beginning of the volume. One data of each pair is the physical ID of the N-th tape mark. The other data of the pair is the absolute block number of the tape mark N. This value is the absolute block number of the last block with the same file number as the tape mark. With the physical ID and the absolute block number of the tape mark, the position of the tape mark can be precisely detected. Thus, a desired physical position on the tape can be accessed at a high speed. 
     The ID address of the UT is the physical ID of the VIT plus 39. The UT is information that represents whether or not a volume has been updated. Before a volume has not been updated, a word (four bytes) that represents the update status of the UT is FFFFFFFFh (h represents hexadecimal notation). After a volume has been updated, the word is 00000000h. 
     The UIT is optional. The UIT is an area of for example 100-IDs. The UIT is a user accessible data table for storing a user header. 
     In this example, 1-ID is assigned to each track set composed of four helical tracks. The logical structure of a data block is defined for each track set. FIG. 11 shows the structure of a logical track set. The first four bytes of the logical track set are used for a format ID that is FFFF0000h. 
     The next 136 bytes (34 words) are used for an area for sub-code data. The sub-code data is composed of management information of a track set thereof. The sub-code data includes for example the above-described tables (such as VSIT, VIT, and BST) and ID codes (such as user data and tape marks). 
     The bytes of which the length of the block management table is subtracted from the next 116884 bytes are used for a user write area. When the track set is used for a user data write area, if the size of the user data is smaller than the size of the user data write area, dummy data is filled in the rest of the areas User data is followed by the block management table area. The length of the block management table is up to 4096 bytes. The last four bytes of the track set are used for a last code (0F0F0F0Fh) of the track set. The last code is preceded by a reserved area of 12 bytes. The block management table is used to manage the structure of a data block of user data. There are four types of track sets defined in the user data area, namely, a user data track set used for writing user data, a tape mark (TM) track set for representing a tape mark, an EOD (End of Data) track set for representing EOD, and a dummy track set for representing dummy data. For each track set type, a sub-code and a block management table are defined. 
     User data is followed by the block management table area. The length of the block management table is up to 4096 bytes. The last four bytes of the track set are used for a last code (0F0F0F0Fh) of the track set. The last code is preceded by a reserved area of 12 bytes. The block management table is used to manage the structure of a data block of user data. 
     FIG. 12 is a schematic diagram showing a magnetic tape on which data is recorded by a data recorder. Data is recorded on a magnetic tape  91  in a record direction shown in the drawing. The magnetic tape  91  has an invalid data portion  92  (including a non-record portion), a record portion  93  (in which data has been recorded), an invalid data portion  94  (disposed between record portions (the invalid data portion  94  includes a non-record portion), a record portion  95  (on which data has been recorded (the record portion  95  includes a non-record portion)), and a non-record portion  97  (disposed between a logical tape last edge  98  and a physical tape last edge  99 ). 
     When data is recorded at the record portion  95 , as a result of a signal process, if the C2 decoder  45  detects an uncorrected error at an uncorrected error point  100 , data that just precedes the error point  100  is invalidated. In this case, the data to be recorded is recorded at the record portion  95 . Next, six methods for a data write retry operation and a data read retry operation for the magnetic tape  91  will be described. In the following description, it is assumed that data has been recorded at the record portion  95  and that an uncorrected error has taken place at the error point  100 . The write retry operation is performed until data is correctly recorded for example up to 10 times. 
     (1) The magnetic tape  91  is prerolled to a preroll point  102  of the record portion  95 . When an uncorrected error is detected by the C2 decoder  45 , it is determined that data just preceding the error point has not been recorded. Thus, the record portion  95  is treated as a bad spot. The record portion  95  is registered to the BST. The preroll point  102  is the top position of a tape tuning area necessary for an image connecting record operation. In addition, the preroll point  102  is set corresponding to the present position of the tape. The length between the preroll point  102  and the error point  100  is set to at least the length necessary for servo lock for the recording operation. 
     When the magnetic tape  91  is loaded, digital data information is read from the DIT by the system controller  81 . When the C2 decoder  45  detects an uncorrected error, it sends an uncorrected error generation signal to the system controller  31 . The system controller  31  sends a control signal to the motor drive circuit  49  corresponding to the signal. The motor  50  is driven corresponding to the control signal and thereby the magnetic tape  91  is prerolled to the preroll point  102 . After the magnetic tape  91  is moved to the error point  100  (invalid data portion), the write retry operation is performed. 
     (2) The magnetic tape  91  is prerolled to the preroll point  103  of the record portion  93 . In this case, data is recorded by the image connecting record operation. The length between the preroll point  103  and the error point  100  is set at least the length necessary for servo lock for the recording operation. The magnetic tape is prerolled to the preroll point  103 . Just after the magnetic tape  91  is moved to the error point  100 , the write retry operation is performed. 
     (3) The magnetic tape  91  is fast-forwarded to a search point  104  of the invalid data portion  96 . Thereafter, the operation of the method (1) is performed. The fast-forward operation to the search point  104  is performed with an ID counter. The ID counter is composed of a servo circuit of the mechanism controller  48  (see FIG.  6 ). The servo circuit of the ID counter counts the relative tape length with IDs calculated corresponding to the length of the outermost diameter of the magnetic tape  91  and the angle of the reel that is rotated. 1-ID recorded on the tape is equivalent to one count of the ID counter. With the ID counter, the top of any record portion of the magnetic tape can be detected for every ID at a predetermined accuracy. 
     (4) The magnetic tape  91  is rewound to a search point  105  of the invalid data portion  94 . The rewind operation is performed with the ID counter. Thereafter, the operation corresponding to the method (1) is performed. 
     (5) The magnetic tape  91  is rewound to a search point  106  of the invalid data portion  92 . Likewise, the rewind operation is performed with the ID counter. Thereafter, the operation corresponding to the method (1) is performed. 
     (6) The magnetic tape  91  is fast-forwarded to a search point  107  of the non-record portion  97 . 
     Likewise, this fast-forward operation is performed with the ID counter. Thereafter, the operation corresponding to the method (1) is performed. 
     As described above, when an uncorrected error takes place, the magnetic tape is prerolled, rewound, or fast-forwarded. Thus, the problem of the head clogging can be solved and the write retry operation for data can be performed. While a head clogging takes place while the record portion  95  is being reproduced, in the same manner as the recording mode, the magnetic tape  91  is prerolled, rewound, or fast-forwarded. When the magnetic tape is reproduced, if an error is detected at an uncorrected error point  101 , the magnetic tape is prerolled, rewound, or fast-forwarded in the above-described manner. Thus, the read retry operation for data just preceding the error point  101  is performed. The read retry operation may be performed from the beginning of the data that precedes the error point  101 . The read retry operation for data is performed until the data is correctly reproduced (for example, up to five times). The above-described six methods may be performed independently or as a combination thereof. When the above-described methods are used as a combination, the problem of the head clogging can be more accurately solved. The fast-forward operation or the rewind operation is performed depending on whether the tape is moved from an error point to a closer preroll/search point in the forward direction or the reverse direction. 
     In the above-described embodiment, the present invention is applied to a data recorder. However, it should be noted that the present invention can be applied to for example a helical scan type video tape recorder. In the above-described embodiment, the system controller  46  controls the mechanical controller  48  and thereby the motor  50  is rotated so that the magnetic tape is moved in the predetermined direction. However, the mechanical controller  48  may be controlled on the host computer side or by another unit that performs the same operation (for example, a dedicated experimental data collecting unit) through the SCSI controller  32 . 
     According to the present invention, when an uncorrected error is detected while data is being recorded or reproduced, the magnetic tape is prerolled, rewound, or fast-forwarded. Thus, the problem of the head clogging is solved. Thereafter, the write retry operation or read retry operation for data is performed. Thus, the efficiency of the recording and reproducing operations can be improved. In addition, time necessary for repeated recording and reproducing operations can be reduced. 
     Although the present invention has been shown and described with respect to a best mode embodiment thereof, it should be understood by those skilled in the art that the foregoing and various other changes, omissions, and additions in the form and detail thereof may be made therein without departing from the spirit and scope of the present invention.