JP3250449B2 - Magnetic tape controller - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic tape control device for controlling a magnetic tape device, and more particularly to a technique for relieving a magnetic tape device by retrying when an off-track is detected when reading a magnetic tape.

[0002]

2. Description of the Related Art As recording densities of magnetic tapes such as cartridge tapes and cassette tapes have increased, and data processing speeds for writing and reading data have also increased, magnetic heads have been increasingly used. In recent years, a technique for quickly and accurately positioning data at the data position of the target track has become increasingly important.

In such a magnetic tape, a serpentine recording format is used. That is, BOT (Begi
Track 0 is defined in a direction (forward direction) from the beginning of the tape called Ning of Tape to the end of the tape called EOT (End Of Tape).
Track 1 is defined in a direction (reverse direction) from OT to BOT.

There are generally two types of serpentine recording formats as shown in FIGS. 4A and 4B, and data is recorded and reproduced in a direction suitable for each track.

In each track, a plurality of data blocks and tape marks indicating their delimiters are arranged in order. At the end of each data block, an identification number for identifying each data block is recorded as data.

Although an identification number is not recorded in a tape mark, it is used to identify a data block on a file basis when a magnetic head is positioned at a target data block.

FIG. 5 shows a recording format of a magnetic tape. FIG.
3 is a magnetic track, 4 in FIG. 5 is an identification number of a data block, 5 in FIG. 5 is a tape mark, and 6 in FIG. 5 is a data block.

FIG. 5A shows that a plurality of data blocks 6 and tape marks 5 are sequentially arranged in the track direction, and FIG. 5B shows an identification number assigned to the last part of the data block 6. To indicate that FIG. 5C shows a data block 6 using an identification number 4 and a tape mark 5.
Indicates that is identified.

On the other hand, magnetic heads for writing or reading data in such a recording format are arranged in the magnetic tape device one by one in the width direction of the magnetic tape corresponding to each of the parallel tracks.

FIG. 6 shows a case where an 18-track magnetic tape from track 0 to track 17 is read / written by a 36-track magnetic tape device having 36 heads from head 0 to head 35.

In this case, the track 0 is controlled to be read and written by the head 0, and the track 1 is controlled to be read and written by the head 2. 36
When a track magnetic tape is read / written by a 36-track magnetic tape device, the track 0 is read / written by the head 0 and the track 1 is read / written by the head 1.

When a write head for recording and a read head for reproducing the recording are different, as in the case of reproducing a recording on a magnetic tape medium having different numbers of tracks and recording densities, a reading error occurs during the reproduction. May be. This is caused by the relative displacement between the track and the head due to the difference in the magnetic head between the devices, and is called off-track.

[0013] Offtrack is inevitable as a machine difference between devices, and is excluded from retry targets as a permanent error that cannot prevent offtrack, detects offtrack, and prevents offtrack. Various techniques have been devised for this purpose.

For example, a technique of providing track identification information to prevent data destruction and accurately position the magnetic head (eg, Japanese Patent Laid-Open No. 62-042353, a track identification method), or detects that a read error is an off-track error. For this purpose, a technique of sliding a magnetic head in the width direction of a magnetic tape (for example, an off-track detection method of a magnetic tape device disclosed in Japanese Patent Application Laid-Open No. Hei 2-301012) has been devised.

In order to avoid off-track, a plurality of electromagnetic transducers for reproduction are arranged at positions where they do not overlap in the running direction of the recording track, and when a reading error is detected, another reproducing electromagnetic transducer corresponding to the same recording track is used. Techniques using an electromagnetic transducer for reproduction (for example, see Japanese Patent Application Laid-Open No.
1 Magnetic recording data reproducing method and magnetic storage system)
Has been devised.

[0016]

When off-track occurs during data reading, as is well known, a reading error is detected, and the data reading is retried by positioning the head of the data block on the magnetic head. .

However, in the conventional magnetic tape control apparatus, even if the retry is performed up to 15 times, an error may occur forever. On the other hand, a space file command and a locate command are prepared as positioning commands for positioning the magnetic tape at a desired data block of a desired track.

The space file command skips the data block to the designated data file and positions the magnetic head at the beginning of the desired data file. The locate command positions the magnetic head at the head of a desired data block while reading the identification number of the data block up to the designated data block.

In an error recovery process for a defective medium such as a case where a magnetic tape having a write error due to a failure of a magnetic tape device is rewritten by another magnetic tape device, a locate command is issued by locating the magnetic head to the magnetic tape. It is used as a means for positioning immediately before or immediately after a location.

However, in the conventional magnetic tape control device, the space file command is a means for finding a tape mark, and is excluded from retry targets.
Therefore, when the designated tape mark is off-track, the reading is skipped, and there is a problem that the tape mark is positioned at the next tape mark.

Further, when performing the error recovery process using the locate command, if the designated position is off-track, a positioning error occurs, and it takes time to retry the locate command.

FIG. 7 shows the operation of a conventional positioning command.
FIG. 7A shows a case where a space file command is executed.
FIG. 7B illustrates a case where a locate command is executed. In FIG. 7A, the data block DB2, the tape mark TM1, and a part of the data block DB3 are off-track. A command was issued to position the tape mark TM1 in accordance with the space file command. However, the tape mark TM1 is off-track and cannot be detected, indicating that the tape mark TM1 is moved to the position of the next tape mark TM2.

In (2) of FIG. 7, the data block D
Off-track is performed from B3 to the middle of the data block DB5. Data block DB by locate command
No. 4 was issued, but the identification number of the data block DB5 was read, and off-track was detected (in the figure) because the order of the identification numbers was incorrect, and the position returned to the last readable identification number (see the figure). ), Retry the locate command from that position (shown in the figure).

In (2) of FIG. 7, the data block D
Despite the fact that both B3 and data block DB4 are off-track, the position specified by the command is set as the expected value, so that it cannot be retried unless the data passes through data block DB4 whose positioning is specified and proceeds to data block DB5. There is a problem.

In general, the retry is performed up to eight times. However, since the retry is performed with the same head, an error may occur forever. In view of such a point, the present invention improves retry processing based on off-track when executing a read command, and performs retry processing when off-track is detected during execution of a space file command. It is an object of the present invention to provide a magnetic tape control device that improves retry processing based on off-track and reduces retry time when a command is executed.

[0026]

The above-mentioned object is achieved by the magnetic tape control device of the present invention constructed as follows. A magnetic tape control device of the present invention controls a magnetic tape device having a first magnetic head for reading data recorded on parallel tracks of a magnetic tape, and a second magnetic head adjacent to the first magnetic head. a magnetic tape controller, when detecting an off-track, the first identification number of the previous off-track detection in the magnetic head is read to
Backspace means for rewinding the magnetic tape to a position where it can be read out, and retry means for switching the first magnetic head to the second magnetic head and restarting reading.

According to the present invention, since retry is started from a data block for detecting off-track, it is possible to make a retry target even if the command is not a conventional retry target, and it is also possible to specify an identification number specified by the command. Since the retry is performed without depending on the retry, the retry processing time can be reduced.

Further, when off-track is detected by the first magnetic head, the retry is performed by the adjacent second magnetic head. Therefore, even if it is not possible to remedy conventionally, off-track can be remedied by retry.

FIG. 1 shows the principle of the present invention. FIG. 1A shows the correspondence between a magnetic head and a magnetic track. FIG.
1 is a first magnetic head, and 2 in FIG. 1 is a second magnetic head adjacent to the first magnetic head 1. 3 in FIG.
Is a magnetic track which is usually read or written by the first magnetic head 1. In the present invention, the magnetic track 3 is read by the second magnetic head 2 when the off-track is detected and the reading is retried.

In FIG. 1, the identification number of the data block of the magnetic track 3 is recorded at 4. Reference numeral 5 in FIG. 1 is a tape mark indicating a break of a data block. 1 indicates a data block following the tape mark 5.

FIG. 1B is a diagram for explaining the magnetic tape control device of the present invention. Reference numerals 7, 8 and 9 in FIG. 1 denote off-track detecting means, backspace means and retry means of the present invention, respectively, and reference numeral 10 in FIG. 1 denotes a magnetic tape control device of the present invention.

When the off-track detection means 7 detects that an off-track occurs in the magnetic track 3, the back space means 8 moves the magnetic tape so that the magnetic head comes to the position of the identification number 4 before the off-track detection. .

When the magnetic tape returns to a predetermined position by the backspace means 8, the retry means 9 changes the magnetic head at the time of retry from the first magnetic head 1 to the second magnetic head 2, and performs retry. Start.

[0034]

Embodiments of the present invention will be described in detail with reference to the drawings. FIG. 3 shows the configuration of the magnetic tape control device and the magnetic tape device of the present invention. Reference numeral 10 in FIG. 3 denotes a magnetic tape control device according to the present invention, which is provided with an off-track detecting unit, a back space unit, and a retry unit, similarly to the magnetic tape control unit 10 in FIG. Reference numeral 20 in FIG. 3 denotes a magnetic tape device controlled by the magnetic tape control device of the present invention. The meanings of the other symbols are the same as in FIG.

While the read command is being executed from the magnetic tape device 20 to the magnetic tape control device 10, a data block signal indicating that data in the data block is being transmitted is transmitted. The magnetic tape control device 10
The data block signal is received by the off-track detection means 7, and the data format of the data block is monitored for abnormality.

The off-track detecting means 7 reads the identification numbers of the data blocks and monitors whether the identification numbers come in order. If the data block signal cannot be received correctly or if the order of the identification numbers of the data blocks cannot be maintained, the off-track detecting means 7 detects it as an off-track error.

FIG. 2 is a view for explaining an embodiment of the present invention. FIG. 2A shows a case where the space file command is executed. In (1) of FIG. 2, the data block DB
2, the tape mark TM1, and a part of the data block DB3 are off-track.

A command was issued to position the magnetic head at the tape mark TM1 according to the space file command. However, since the tape mark TM1 is off-track,
The tape mark TM1 cannot be detected, and the tape mark TM1 is not detected.
The magnetic tape moves to the position where the identification number of the next data block DB3 is read. The off-track detecting means 7 of the magnetic tape control device 10 (shown in FIG.
In some cases, it is detected that the data block DB2 is off-track, but at that time, it cannot be detected whether the tape mark 1 is still off-track. Only after reading the identification number of the data block DB3 is the tape mark T
It is detected that M1 is off-track.

The magnetic tape control device 10 has an identification number (DB
3) exceeds the expected value (the identification number of TM1), so that the backspace means 8 returns to the position of the last readable identification number (data block DB1).
To the magnetic tape device 20. The magnetic tape device 20 executes the backspace, and the magnetic tape returns to the position of the data block DB1. Subsequently, the magnetic tape control device 10 of the present invention changes the magnetic head at the time of retry from the first magnetic head 1 to the second magnetic head 2 and starts retrying. 9
To the magnetic tape device 20.

The magnetic tape device 20 continuously retries the space file command from that position, and positions the space file command behind the desired tape mark TM1 (ie, at the head gap position of the data block 3). As described above, according to the magnetic tape control device of the present invention, when the space file command is executed, the specified tape mark is not skipped and positioned to the next tape mark.

Even if the tape mark is once read off-track, the magnetic head is correctly positioned at the tape mark by retry. FIG. 2B shows a case where a locate command is executed. (2) of FIG. 2 is (2) of FIG.
Similarly to data block DB3 and subsequent data blocks DB
5 is off-track halfway.

Data block DB by locating command
4, the off-track detecting means 7 of the magnetic tape control device 10 cannot correctly receive the data block signal of the data block DB3, so that the data block DB3 is off-track. Is detected. At the time of reading the data blocks DB3 and DB4, if the data block signal is correctly received and the off-track cannot be detected, the data block DB5 is read.
When the identification number is read, off-track is detected as in (2) of FIG. 7 because the order of the identification numbers is invalid.

Subsequently, when detecting the off-track, the magnetic tape control device 10 instructs the magnetic tape device 20 to return to the position of the identification number (data block DB2) that can be read last by the backspace means.

The magnetic tape device 20 executes the backspace, and the magnetic tape returns to the position of the data block DB2. The magnetic tape control device 10 causes the retry means 9 to change the magnetic head for retry from the first magnetic head 1 to the second magnetic head.
The magnetic tape device 20 is instructed to start a retry instead of the magnetic head 2 of FIG.

The magnetic tape device 20 continuously retries the locate command from that position, and positions it at the head of the desired data block DB4 (ie, at the head gap position of the data block 4). Thus, according to the magnetic tape control device of the present invention, the retry of the locate command is performed by the second magnetic head 2 instead of the first magnetic head 1, so that the retry may be successful. Will increase dramatically.

Conventionally, as shown in FIG. 7 (2), there is a problem that the retry cannot be performed unless the data block DB5 is reached. In the magnetic tape control device of the present invention, if an off-track is detected, Since the retry is performed immediately, the retry processing time can be significantly reduced as compared with the related art.

In both the retry of the space file command and the retry of the locate command, the retry is started by the second magnetic head 2.
Off-track may be detected by the second magnetic head 2 in some cases. In that case, the first magnetic head 1 is retried again. By repeating this, retry is performed up to eight times in total.

Although off-track may be detected even after a total of eight retries, this is reported as a permanent off-track error. FIG. 2C shows a case where a read command is executed. In (3) of FIG. 2, the data block DB3 and thereafter are off-track.

A data block DB is read by a read command.
During the reading of data No. 3, the off-track detecting means 7 detects that the data block DB3 is off-tracking because the data block signal cannot be correctly received. Subsequently, when detecting the off-track, the magnetic tape control device 10 instructs the magnetic tape device 20 to return to the position (data block DB2) of the identification number that can be finally read by the backspace means. The magnetic tape device 20 executes the backspace, and the magnetic tape returns to the position of the data block DB2. The magnetic tape control device 10 causes the retry means 9 to change the magnetic head for retry from the first magnetic head 1 to the second magnetic head.
The magnetic tape device 20 is instructed to start a retry instead of the magnetic head 2 of FIG.

The magnetic tape device 20 continuously retries the read command from that position. Retry of the read command (up to 15 times) can be performed up to 15 times with the first magnetic head 1 and the second magnetic head.
Alternately with the magnetic head 2.

In the embodiment of the present invention, the space file command, the locate command, and the read command have been described. However, the present invention can be applied to the case of retrying other equivalent commands. Needless to say.

[0052]

As is apparent from the above description, according to the present invention, the retry is started from the position where the off-track is detected. The retry is performed independently of the specified identification number, so that the retry processing time can be shortened. Further, when off-track is detected, the retry is performed by the adjacent magnetic head. There are various effects that a remedy can be performed even if it cannot be remedied conventionally.

[Brief description of the drawings]

FIG. 1 is a principle diagram of the present invention.

FIG. 2 is an embodiment of the present invention.

FIG. 3 shows the configuration of the magnetic tape control device of the present invention.

Fig. 4 Serpentine recording format

Fig. 5 Recording format of magnetic tape

FIG. 6 Correspondence between a magnetic track and a magnetic head

FIG. 7 shows a conventional positioning command operation.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 first magnetic head 2 second magnetic head 3 magnetic track 4 identification number 5 tape mark 6 data block 7 off-track detecting means 8 backspace means 9 retry means 10 magnetic tape control device 20 magnetic tape device

Claims (1)

(57) [Claims] 1. A magnetic tape control for controlling a magnetic tape device having a first magnetic head for reading data recorded on parallel tracks of a magnetic tape, and a second magnetic head adjacent to the first magnetic head. an apparatus, when detecting the off-track, at the first magnetic head
Backspace means for rewinding the magnetic tape to a position where the identification number before off-track detection can be read, and retry means for switching the first magnetic head to the second magnetic head and restarting reading. A magnetic tape control device, comprising: