JP2000311470A - Magnetic tape device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable the restoration processing of original data without affecting a host device when erroneous overwriting is performed by controlling a buffer so that data already written is read out to a buffer before writing. SOLUTION: When continuity exists in a block number between lookahead data left in a buffer 3 and a first block normally read, as interpolation can be performed by loockahead data in the buffer 3, the lookahead data in the buffer 3 is held as it is, a record signal of a magnetic tape 13 before a block X is reproduced and the reproduced data is written in the buffer 3. When the last end of data is reproduced before the buffer 3 is filled with reproduced data, the magnetic tape 13 is positioned so that data can be written from the head of data of a block received first out of write-in data, lookahead data in the buffer 3 is read out, and restoration is performed by starting recording from the position already positioned as mentioned above.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a magnetic tape device, and more particularly to a magnetic tape device for recording information data on a magnetic tape.

[0002]

2. Description of the Related Art When a read command is received from a host device, data recorded on the magnetic tape is read from the magnetic tape by a reproducing head and transferred to the host device.
Also, a magnetic tape device is known in which when a data write command is received from a host device to a magnetic tape device, input data is written on a magnetic tape by a recording head.

[0003]

However, in the above-described magnetic tape device, if another data is erroneously overwritten on a portion where the necessary information is already recorded on the magnetic tape, the necessary information before the overwriting is overwritten. There is a problem that cannot be restored.
In a device such as a hard disk device capable of random access, when newly recording data, by writing to the oldest area among unused areas or erased areas, the previously erased information can be restored. It has become. However, in a sequential access device such as a magnetic tape device, such a method cannot be used, and necessary information before overwriting has been replaced by the overwritten information, so that it cannot be restored.

[0004] The present invention has been made in view of the above points,
By controlling the buffer so that the written data is read into the buffer before starting writing, if the data is accidentally overwritten, the original data can be restored without affecting the host device. It is an object to provide a possible magnetic tape device.

[0005]

In order to achieve the above object, the present invention temporarily stores a plurality of block data input from a host device during recording, and stores the stored block data during reproduction in a host device. A buffer for transferring data to a magnetic tape, a block drive for recording block data on a magnetic tape, and a tape drive for reading the recorded block data from a magnetic tape by a reproducing head. It is determined whether or not the desired block data is stored in the buffer. If the block data is stored, the desired block data is transferred to the host device. When the block data is reproduced and stored in the buffer, the desired block data is transferred to the host device. Thereafter, one or two or more block data subsequent to the desired block data are reproduced and sequentially stored in a buffer. When a write command is received from a higher-level device, whether or not the block data to be written is stored in the buffer is determined. Judgment, if not stored, controls the tape drive to reproduce a fixed amount of buffer data consisting of block data to be written and one or more subsequent block data from the magnetic tape and sequentially store them in the buffer Control means for reading out when a certain time has elapsed after receiving or receiving a command that requires ejection of the buffer, inputting it to a tape drive, recording it on a magnetic tape, and clearing recording block data from within the buffer; Is a magnetic tape device having:

Here, according to the present invention, when the above-mentioned control means receives a write cancel command from the host device, the first block data received among the write block data remains in the buffer when the write block data is left in the buffer. Clears the write reservation to the magnetic tape, and if the first received block data is not left in the buffer, the first recorded block data is reproduced by reproducing the recording block data preceding the write block data on the magnetic tape. Judge whether the block data and the block data held in the buffer are continuous, and if so, replace the recorded block data ahead of the first block data that was normally reproduced on the magnetic tape with the data Play until the end signal is detected, write it in the buffer, and then drive the tape drive. After the recording head is positioned at the recording position immediately before the first received block data of the write data on the magnetic tape, the buffer in the sequence following the recording block immediately before the first received block data from the recording position The block data stored in the memory and the block data reproduced and stored are sequentially read from the buffer and recorded on a magnetic tape.

Further, the present invention provides the above-mentioned control means
Reproduces the recording block data after the first block data that was normally reproduced on the magnetic tape, writes the reproduced data in the buffer, and writes the reproduced data to the full capacity of the buffer without detecting the data end signal. Is transferred, after transferring the block data in the buffer,
The reproduction of the magnetic tape is continued until the end of data signal is detected, the reproduced data is transferred to the host device, and the host device performs a restoration process. Then, the tape drive is controlled to move the recording head on the magnetic tape. After positioning the block data immediately before the first received block data among the write data, receiving the restored block data from the host device and recording the block data on the magnetic tape in order from the positioned recording position. Features.

Further, the present invention, when receiving the write cancel command from the host device, checks whether or not the magnetic tape recording block data before being overwritten by the write block data remains in the buffer. When remaining, the block data from the beginning of the magnetic tape to the block data just before the first received block data is reproduced and written into the buffer while retaining the block data in the buffer. Controlling the recording head to position the recording head immediately after the last-ordered block data in the buffer on the magnetic tape, and recording the block data in the buffer on the magnetic tape running in the reverse order toward the beginning of the tape. It is characterized by having done.

Further, according to the present invention, the control means reproduces the recording block data preceding the first block data normally reproduced on the magnetic tape, writes the reproduced data in a buffer, When the playback data is written to the full capacity of the buffer without detecting a signal, the tape drive is controlled to position the recording head at the recording position immediately before the first received block data among the write data on the magnetic tape. After the block data in the buffer is sequentially recorded on the magnetic tape by a predetermined amount, the reproducing head is positioned immediately after the tape recording position of the last-ordered block data in the buffer to reproduce the magnetic tape by a predetermined amount. The operation is performed until the block data is reproduced, and the writing of the reproduced block data to the buffer is performed at the data end. Characterized by being configured to repeat to the detection of the signal.

In the present invention, when recording or reproducing desired block data on or from a magnetic tape, the buffer is controlled so that not only the desired block data but also a plurality of subsequent block data are written and held in the buffer. Therefore, when a write cancel instruction is received from the host device, it can be replaced with the overwritten block data using the block data in the buffer. In this specification, "block data" is a generic term for "block" and "data", and a block generally has a configuration in which redundant bits such as a header are added to data.

[0011]

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a block diagram of a first embodiment of a magnetic tape device according to the present invention. The magnetic tape device 1 according to the first embodiment shown in FIG. 1 is connected to a host device 2 such as a host computer that issues a command to read / write (record / reproduce) a magnetic tape. The magnetic tape device 1 runs a magnetic tape 13 and records and reproduces data on and from the magnetic tape 13. The magnetic tape device 1 interprets commands from the host device 2, and a control unit 11 that operates the tape drive 10. Data and tape drive 10
A buffer 3 for temporarily storing data reproduced from the tape drive 1, a recording circuit 4 for converting data from the host device 2 into a signal for recording by the tape drive 10, and a tape drive 1.
The reproduction circuit 5 converts the signal reproduced at 0 to data to be transferred to the host device 2, and the storage unit 16.

The tape drive 10 rotates a reel 9 in accordance with a signal from a control unit 12 in a control unit 11 to drive a magnetic tape 13, two reels 9 rotated by the drive circuit 8, Both ends are wound around two reels 9, and a magnetic tape 13 running by rotation of the reel 9 is located at a position where the magnetic tape 13 is in contact with the magnetic tape 13 between the two reels 9, and a signal from the recording circuit 4 is transmitted to the magnetic tape 13. Recording head 6 for writing and magnetic tape 1
3 and a reproducing head 7 for reading out the signal recorded in 3 and sending it to the reproducing circuit 5. The control unit 11 is a control device that operates under program control. The program is stored in the storage unit 16, and the control unit 12 that interprets a command input from the host device 2 and controls the drive circuit 8 is controlled. Including.

Next, the operation of this embodiment will be described. The data recorded on the magnetic tape 13 is transferred to the host device 2
When reading the data, the control unit 12 interprets the command received from the host device 2 and determines whether or not the data to be read is stored in the buffer 3. If no data is stored in the buffer 3, the driver 8 operates the drive circuit 8,
The reel 9 is rotated, and the magnetic tape 13 is operated. As the magnetic tape 13 travels, the data recorded on the magnetic tape 13 is reproduced by the reproduction head 7, the reproduction circuit 5 converts the reproduction signal, and stores the converted signal in the buffer 3. And
When the data of the block to be read is stored in the buffer 3, the data is transferred to the host device 2.

In particular, if the next operation is not specified, the magnetic tape 13 is run as it is, reproduced as much as it enters the buffer 3, and the data of the reproduced block is stored. When reproducing the data of the next block, the data is written until it can be stored in the buffer 3. When reading the data of the next block, since the data has been written in the buffer 3, the data is transferred to the host device 2 without operating the magnetic tape 13 again.

Next, the processing of the control means 12 when writing data from the host device 2 to the magnetic tape 13 will be described in detail with reference to the flowchart of FIG. 2 and FIG. The control means 12 transmits the information from the host device 2 to the magnetic tape device 1
Receives the data write command (step A1),
It is determined whether or not the previous command using the buffer 3 was a write command (step A2). If it is not a write command, it is determined whether or not there is prefetch data (valid prefetch data) of the block to be written in the buffer 3 (step A3).

If there is no valid prefetch data, it is determined whether or not the tape position matches the current position reported to the host device 2 (step A4). If there is a deviation, the tape position is corrected to the position reported to the host device 2 (step A5). If it is determined in step A4 that the tape position is correct, or if the tape position is corrected in step A5, pre-reading is performed up to a certain amount (for example, about 1/2) of the buffer 3 (step A6). ). If valid prefetch data is stored in the buffer 3 in step A6, or if it is determined in step A3 that there is valid prefetch data to be written in the buffer 3, the tape position is returned by the prefetch amount. (Step A7).

After the tape position is returned in step A7, or when it is determined in step A2 that the previous command to use the buffer 3 was a write command, the buffer 3 is stored in the buffer 3 as long as the write data to be stored is entered. It is determined whether there is a free area (step A8). If there is no free area, it is determined whether there is write data in the buffer 3 (step A9). If there is no write data, the most unnecessary prefetch data is discarded (step A10). Then, the write data in the buffer 3 is written on the magnetic tape 13 to empty the buffer 3 (step A11).

The "most unnecessary prefetch data" in step A10 is the prefetch data of the block farthest from the current tape position. Step A10 or A
By the processing of No. 11, an empty area is secured in the buffer 3, and the write data is received and written into the buffer 3 (step A12). This completes the write processing on the upper side (step A13).

The data written in the buffer 3 is transferred to the magnetic tape 13 when a certain period of time has elapsed or when the magnetic tape device 1 receives a command such as a positioning command that requires a buffer flush (buffer flush). Is written out. That is, in this case, the control means 12 operates the drive circuit 8 to rotate the reel 9 and
To work. The data stored in the buffer 3 is read and converted by the recording circuit 4 and then supplied to the recording head 6. As is well known, the recording head 6 writes data input from the recording circuit 4 to the magnetic tape 13 running in contact.

Next, the operation of the write cancel instruction will be described in detail with reference to the flowchart of FIG. 3 and FIG. When the host device 2 wants to cancel the immediately preceding write command, it issues a cancel command to the magnetic tape device 1. When the control means 12 in the magnetic tape device 1 receives the cancel command from the host device 2 (step B1), first,
It is checked whether the data of the block received first among the write data remains in the buffer 3 (step B2).

If the data remains in the buffer 3, the data has not yet been recorded on the magnetic tape 13, so that only the write reservation to the magnetic tape 13 is cleared, and the write command canceling process ends (step B11). ).
If the data received first among the write data does not remain in the buffer 3, the data of the block has already been recorded on the magnetic tape 13. The recording signal is reproduced to read the end of the data of the written block. The first block that can be read normally is set to X, and it stops at that location (step B3).

Subsequently, it is determined whether there is a gap between the pre-read data remaining in the buffer 3 and the first normally read block, that is, whether there is a discontinuity in the block number (step B4). If the data is lost (discontinuous), the data cannot be restored and the process is terminated (step B5). On the other hand, when there is continuity in the block number between the prefetched data remaining in the buffer 3 and the first block that can be read normally, the complement can be performed with the prefetched data in the buffer 3. While reproducing the recording signal of the magnetic tape 13 ahead of the block X while holding the pre-read data of the block X, the reproduced data is written to the buffer 3 (step B6).

If the end of data (EOD) is reproduced before the buffer 3 becomes full with the reproduced data, the write start position, that is, the head of the data of the first received block of the write data (write cancel command is issued) The magnetic tape 13 is positioned so that data can be written from (before the data of the first block) (step B9). Then, the pre-read data in the buffer 3 is read out, and recording is started from the above-mentioned position, thereby completing the restoration work. On the other hand, in step B7, EOD
If it is determined that the buffer 3 is full of the reproduction data before the detection is performed, the buffer 3 is transferred to the host device 2 and the restoration processing is performed (step B8).

Next, the restoration processing in the above step B8 will be described with reference to the flowchart of FIG. First, the host device 2
To the data download request (step C
2). When the upper device 2 is ready for copying, the upper device 2 issues a copying command to the magnetic tape device 1. When the control means 12 receives a siphoning command (command) from the host device 2 (step C)
3), the data of the block in the buffer 3 is transferred to the block N +
The data from the data No. 1 to the current position is transferred to the host device 2 (step C4).

When a free area is created in the buffer 3, the data is read from the current position and transferred to the host device 2 (step C5). If the read block is not EOD,
Further reading is continued (step C6). If EOD is detected, it is positioned at the writing start position (step C7). Then, the data of the restoration processing is received from the host device 2 and written to the magnetic tape 13. After writing everything, the restoration work is completed (step C
8).

Next, the operation will be described more specifically with reference to FIGS. FIG. 5 is a diagram schematically showing the recording state of the magnetic tape in block units, and FIG. 6 is a diagram schematically showing the storage state of the buffer 3 at each time.
Here, it is assumed that the capacity of the buffer 3 is 512 KB, and 50 KB per block.

When the block N is read in accordance with a read command from the host device 2 and transferred to the host device 2, not only the block N but also the magnetic tape 13
6A, the data from block N to block N + 9 is reproduced from the magnetic tape 13 and stored in the buffer 3 from address 0 to address 500 as shown in FIG.

The data of the block N is stored in the buffer 3, but is cleared when the data has been transferred to the host device 2. In this state, when the magnetic tape device 1 receives a write command to the magnetic tape 13 from the host device 2, all buffers 3 are cleared in the conventional device, but in this embodiment, all buffers 3 may be cleared. Instead, try to clear only a part. That is, if the buffer supports storage in the reverse direction, the data required last, in this case, the data of block N + 9, is cleared in order, and stored in the empty area. Further, in the same manner as in the conventional apparatus, the buffer 3 cannot be used in the reverse direction.
(Preferably about 1/2, so that it can be used together)) and store it from that location.

Here, the latter example will be described.
As shown in FIG. 6B, of the blocks N + 1 to N + 9, which are the pre-read data stored in the buffer 3,
Block N + 1 to block N having a capacity of about 1/2
The data up to +5 is retained, the data in blocks N + 6 to N + 9 are discarded, and the next write block, block N + 1 ′, is transferred from the host device 2 from the location where block N + 6 was stored (address 300). Stored.

After a certain period of time, the block N + 1 'in the buffer 3 is recorded on the magnetic tape 13, and when the recording is completed, as shown schematically in FIG.
Data of block N + 1 'is recorded after block N, and a data end mark (EOD) is recorded immediately after that. When the recording of the data of the block N + 1 'is completed, the data of the block N + 1' in the buffer 3 is cleared.

Here, when the host device 2 wants to cancel the writing of the block N + 1 ', it outputs a write cancel command to the magnetic tape device 1, and the control means 12 receives this write cancel command, so that how many blocks can As described above, the recorded information on the magnetic tape 13 ahead of the block N + 1 'is reproduced in order to check whether it remains on the upper side. The recording state of the magnetic tape 13 at this time is schematically shown in FIG. 5B, and by the above-described reproduction, the data end mark (E) follows the block N + 1 ′.
OD), there is a block that has been overwritten and only a part remains, and it can be seen that there is a block N + 4 beyond that. Therefore, this block N + 4 is the block X in step B3 described above.

At this time, the contents stored in the buffer 3 are as shown in FIG.
As schematically shown in (c), the data of the reproduction block N + 4 of the magnetic tape 13 is obtained from the data from the block N + 1 to the block N + 5 which is the pre-read data and the location (address 300) where the block N + 1 'was stored. Is stored.

As can be seen from FIG. 5B, three blocks of data from block N + 1 to block N + 3 have been lost on the magnetic tape 13, but as shown in FIG. Since the data of the blocks from block N + 1 to block N + 5 are held,
Can be complemented. Here, since the block N + 4 overlaps between the magnetic tape 13 and the buffer 3 and N + 5 is to be read from now on, N + 5 and N + 4 read as background data are cleared from the buffer 3 and N + 1 to N
The block N + which is the block X on the magnetic tape 13 is held while the data of the block +4 is held in the buffer 3.
4 starts reproduction of the magnetic tape 13 (step B).
4, B6).

If the EOD is detected before the buffer 3 becomes full of the reproduction data, for example, unlike FIG.
If there is an EOD immediately after block N + 8, restoration is performed in this device. In the restoration operation at this time, first, the relative position between the magnetic tape 13 and the recording head 6 is positioned so that magnetic recording can be performed immediately after the block N, that is, immediately before the block N + 1 'where writing is to be canceled (step B9). ). Next, the pre-read data stored in the buffer 3, from block N + 1 to block N + 4
And the data read from the end of the EOD, block N + 5 to block N + 8 are written. When writing is completed,
The restoration operation is completed.

In the tape recording state shown in FIG.
Before the EOD is detected, the buffer 3 becomes full with the data of the reproduction block. That is, as shown in FIG.
When a part of the data of the block N + 10 is reproduced from the magnetic tape 13 and read into the buffer 3, the buffer 3 becomes full. Therefore, the magnetic tape device 1 requests the upper device 2 to download the data (step S10). C
2).

Thus, upon receiving a siphoning instruction from the host device 2 (step C3), the data of the blocks N + 1 to N + 10 in the buffer 3 is transferred to the host device 2 (step C4), and the magnetic tape 13 sends the data from the magnetic tape 13 to the E.
Until the OD is detected, the data from the block N + 11 to the block M is reproduced on the magnetic tape 13 while reproducing the data on the magnetic tape 13.
(Steps C5 and C6). Thereafter, the data is repositioned immediately after the block N (step C7), and the data from the block N + 1 to the block M downloaded to the host device 2 is transferred from the host device 2 to the magnetic tape device 1 and written on the magnetic tape 13, The restoration process is completed (Step C8).

As described above, in this embodiment, the magnetic tape 13 on which the block N + 1 'has been erroneously written can be restored to the original recording state without adding a special mechanism.

Next, the configuration and operation of the second embodiment of the present invention will be described. The operation of the second embodiment will be described with reference to FIG. In the second embodiment, a function of running the magnetic tape 13 in the opposite direction and recording is added to the recording circuit 4 and the tape drive 10 of the first embodiment shown in FIG. Otherwise, the configuration is the same as that of the first embodiment shown in FIG.

In the second embodiment, after writing the data of the block N + 1 'on the magnetic tape 13 and then canceling the writing, it is first checked whether the head of the block N + 1' can be read and restored. Here, since the data of the block N + 1 to the block N + 4 exist in the buffer 3, the data can be restored. The data of the reproduction block is written to the buffer 3 while the data of the blocks N + 1 to N + 4 are held, until the buffer 3 becomes full. If the buffer 3 is full before EOD is detected, it is checked whether blocks 1 to N + 3 fit in the buffer.

The checking method includes (1) a method of estimating the length by the block length of the immediately preceding block × the number of blocks, and (2) calculating the block length in the buffer each time reading or writing is performed, and starting from the beginning of the tape. And (3) a method of actually reading and checking the block length. Of these, the second method of storing the cumulative length is desirable. The reason is that there is no error,
Also, since the length is checked by the operation of the magnetic tape in advance, the operation of the magnetic tape is unnecessary when checking.

For example, if the buffer capacity is 512 KB and the block length is 50 KB, it is assumed that if N is smaller than 7 in the method (1), it can be estimated that the buffer will fit in the buffer. Then, blocks 1 to N are read. If the data cannot be completely read out and transferred, the data is transferred to the host device 2 and restored by the same method as in the first embodiment. When combined with the data remaining in the buffer, data from block 1 to block N + 3 exists in the buffer. N +
Positioning before 4, and writing in the reverse direction from there toward the beginning of the tape. Block 1 is written, and an area for medium identification at the head of the medium can be written. Thus, the restoring operation is completed. Since the area for medium identification is an area in which the same pattern has been written, there is no problem in rewriting when rewriting.

In the first embodiment, if the head of the tape written almost to the end of the tape is erroneously overwritten, it is necessary to read and write again from the overwritten point to the end in the first embodiment.
(The length of the medium / the speed of the tape at the time of reading) + the rewinding time + (the length of the medium / the speed of the tape at the time of writing). Therefore, the length of the medium is 15
0m, read / write tape speed 2m / sec,
If the rewinding time is 30 seconds, it takes about 180 seconds. On the other hand, if only the head of the tape is rewritten in the opposite direction as in the present embodiment, processing can be performed in a few seconds.

Next, the configuration of the third embodiment of the present invention will be described. FIG. 7 is a block diagram showing a third embodiment of the magnetic tape device according to the present invention. In the figure, the same components as those of FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted. The magnetic tape device 20 according to the third embodiment shown in FIG.
In this embodiment, a reproducing head 14 is added to the tape drive 21 in the first embodiment shown in FIG. 1, and a reproducing circuit 15 for receiving a reproducing signal from the reproducing head 14 is added. The reproducing head 14 is provided at a position opposite to the recording head 6 and at a position opposite to the reproducing head 7 (upstream of the tape during recording) and in contact with the magnetic tape 13. A reproduction circuit 15 is added separately from the reproduction circuit 5. The signal reproduced by the reproducing head 14 is converted into data by the reproducing circuit 15 and stored in the buffer 3.

Next, a write operation in the third embodiment of FIG. 7 will be described with reference to a flowchart of FIG. 8, the same processing steps as those in FIG. 2 are denoted by the same reference numerals. When the control means 12 of FIG. 7 receives the write command from the host device 2, it determines whether the previous command using the buffer 3 was a write command (step A2). If the previous command is not a write command, the pre-read data in the buffer 3 is cleared (step D1), and it is determined whether or not the tape position matches the current position reported to the host device 2 (step A4). ).
If there is a deviation, the tape position is corrected to the position reported to the host device 2 (step A5).

When it is determined in step A2 that the previous command is a write command, or in step A4
If it is determined in step A5 that the tape position is correct, or if the tape position has been corrected in step A5, it is determined whether or not there is free space in the buffer 3 just enough to receive the write data to be stored (step A8). If there is no free area, the write data stored in the buffer 3 is written out to the magnetic tape 13 to empty the buffer 3 (step A11). As long as the write data to be stored is to be entered, the buffer 3 originally has an empty area, or the write data stored in the buffer 3 is written out to the magnetic tape 13 by the
Is cleared, the write data received from the host device 2 is stored in the buffer 3 (step A12).
This completes the write processing on the upper side.

When the write data stored in the buffer 3 has passed for a certain period of time or has received a command such as a positioning command which requires the buffer to be flushed (buffer flush), the control means 12 operates the drive circuit 8 to control the reels. 9 to rotate the magnetic tape 13 in a predetermined direction at the time of recording, read out the data stored in the buffer 3, convert it by the recording circuit 4, supply it to the recording head 6, and contact it to run. To the existing magnetic tape 13. At the same time, the reproducing head 15 reproduces the recording data of the magnetic tape 13 before being written by the recording head 6,
The data is converted by the reproduction circuit 15 and stored in the buffer 3.

When a write cancel command is received, the first
In the same manner as in the first embodiment, it is checked whether the data can be restored using the data remaining on the magnetic tape 13 and the data stored in the buffer 3, and if the data can be restored, a restoration process is performed.

The specific operation will be described with reference to FIGS. As described above, the block N is read out according to the read command from the host
9A, since the magnetic tape 13 is pre-read not only in the block N but also in the buffer 3 as shown in FIG.
As shown in (2), from address 0 to address 500, data from block N to block N + 9 is reproduced from the magnetic tape 13 and stored in the buffer 3.

The data of the block N is stored in the buffer 3, but is cleared when the data has been transferred to the host device 2. In this state, when the magnetic tape device 1 receives a write command to the magnetic tape 13 from the host device 2, in this embodiment, the pre-read data in the buffer 3 is cleared (step D).
1) The data from the block N + 1 ', which is the write data, to the data of the block N + 4' are sequentially stored in the buffer 3 (step A11). The storage state of the buffer 3 at this time is as schematically shown in FIG.

Here, since the free space of the buffer 3 is used for two, one for writing and the other for storing background data, if the total storage capacity is set to about デ ー タ of the total storage capacity, the data of the block N + 5 ′ is subsequently stored in the buffer 3. When the data is written, there is no free space in the buffer 3. Therefore, in order to create a free space, the data in the buffer 3 is written to the magnetic tape 13 at the write start position. At this time, the recording of the magnetic tape 13 is performed by the reproducing heads 7 and 14 so that the recording head 6 is at the write start position between the last recording position of the block N and the first recording position of the block N + 1 in FIG. While the block is being reproduced, the magnetic tape 13 runs in the direction opposite to the recording direction.
Since the magnetic tape 13 is rewound until the data is reproduced, the recording head 6 passes through the write start position to reach the block N-1 direction, and then the magnetic head 13 reaches the write start position. The tape 13 is controlled to run in the same forward direction as during recording, and stops. At this time,
The reproducing head 14 comes to the head recording position of the block N + 3.

At the time of positioning to the recording start position, data of a predetermined number of blocks immediately after the recording start position reproduced by the reproduction head 14 are written to the buffer 3 via the reproduction circuit 15. The predetermined number of blocks is the number of blocks existing between the recording head 6 and the reproducing head 14, and is two blocks here. Therefore, here, the data of the blocks N + 1 and N + 2 reproduced from the magnetic tape 13 by the reproducing head 14 in the forward direction are stored in the buffer 3.

After the positioning to the recording start position, the recording head 6 writes the blocks N + 1 ′ and N +, which are the write data in the buffer 3, on the magnetic tape 13.
2 'are sequentially written, whereby the data of the blocks N + 1' and N + 2 'in the buffer 3 are cleared, and at the same time, the reproduction head 14 reproduces the blocks N + 3 and N + 4. Therefore, the data of these blocks is written into the buffer 3. As a result, the storage state of the buffer 3 is as shown in FIG.
As schematically shown in (c), the write block N +
3 ′ to N + 5 ′, read-ahead blocks N + 1 and N + 2 reproduced by the reproducing head 14 at the time of positioning, and data reproduced from the magnetic tape 13 by the reproducing head 14 at the time of recording each data of the blocks N + 1 ′ and N + 2 ′ of the recording head 6. Each data of the blocks N + 3 and N + 4 is stored.

Further, when the block N + 3 'in the buffer 3 is recorded on the magnetic tape 13 by the recording head 6 and the block N + 5 is reproduced from the reproducing head 14, the data area of the block N + 3' is cleared in the buffer 3. However, since the data of the reproduced block N + 3 is written, there is no place to put the next write data input from the host device 2. Therefore, the prefetch block in the buffer 3 is partially cleared (here, block N + 1).
Is cleared), and the data of the next write block, block N + 6 ′, is stored in the cleared area. As a result, the storage state of the buffer 3 is schematically shown in FIG. As a result, in this example, it is possible to always hold the pre-read data of about four blocks in the buffer 3 during the write operation.

In this embodiment, since the data of the pre-read block reproduced from the position of the magnetic tape 13 immediately before the new data is recorded on the magnetic tape 13 can be written in the buffer 3, the data is recorded when there is no pre-read data. Also, there is no need to pre-read the data to collect background data. Since the data for the area for reading the base data of the buffer always remains after the last writing, that is, in the above-described embodiment, about four blocks of read-ahead data are always stored in the buffer 3 during the writing operation. Since it can be retained, it can always be restored in that range.

Next, a fourth embodiment of the present invention will be described. The fourth embodiment is different from the first embodiment in that the method of the restoration processing is changed and the restoration processing is performed internally. That is, when the information recorded on the magnetic tape 13 is read into the buffer 3 in the restoration processing in the first embodiment, if the information cannot be accommodated in the buffer 3, the recording head 6 is positioned at the write start position. Then, the data of a certain amount of blocks in the buffer 3 is written (recorded) on the magnetic tape 13 from the position where the data is positioned. By this recording, the fixed amount of free space is created in the buffer 3. Then, the reproducing head 7 is repositioned at the place where the reading was stopped, and the reproduction of the magnetic tape 13 is started again from that position. The data of the reproduction block is read into the buffer 3. Repeat this. If EOD is detected during playback operation,
The data is written to the buffer 3 and the restoration process is completed.

Next, the operation of the fourth embodiment will be specifically described with reference to FIGS. The maximum block length that can be written on the magnetic tape (L2 in FIG.
00KB, the length required to write EOD (Fig. 5
Assuming that (b) L1) corresponds to a data length of 100 KB, if the data is stored in the buffer 3 at 300 KB or more, the data can be processed internally without being transferred to the host device 2. Assume that the storage capacity of the buffer 3 is 512 KB, the block length currently written on the tape and the block length to be written from now on are 50 KB.

When the capacity of the buffer 3 becomes full in the restoration processing, the state becomes as shown in FIG. In this state, buffer 3
To the block N on the magnetic tape 13 without data.
The recording head 6 is positioned at a position immediately after the above. In consideration of the area overwritten by EOD, the data of blocks N + 5 to N + 10 stored in the buffer 3 is kept as it is, and the data of blocks N + 1 to N + 4 stored in the buffer 3 is the data of the above block. N to the magnetic tape 1
Write to 3. After that, the block N +
Data from block 1 to block N + 4 is cleared.

Next, the reproducing head 7 is positioned at a position on the magnetic tape 13 immediately after the last block N + 10 in the buffer 3, and the magnetic tape 1 is moved from that position.
3 is started and the data of the reproduced block is stored in the buffer 3.
Store until is full. Since there is a free space of 212 KB, the reproduction data from block N + 11 to block N + 14 is stored in the buffer 3. Next, the recording head 6 is positioned at a position on the magnetic tape 13 immediately after the recording position of the last block N + 4 recorded last time, and the blocks N + 5 to N are stored in the buffer 3.
The data of four blocks up to +8 is stored in the block N
+4 from the position immediately after +4 by the recording head 6
Write to 3. Such processing is repeated, and when the EOD is detected in the reading operation, the data is written to complete the restoration processing.

When transferring and restoring to a higher-level device, there is a possibility that a high-capacity tape cannot be received by the higher-level device. In the fourth embodiment, although the processing is performed internally, it takes time, but the restoration processing can be performed without affecting the host device.

[0060]

As described above, according to the present invention,
When recording or reproducing the desired block data on the magnetic tape, the control method of the buffer was changed so that not only the desired block data but also a plurality of subsequent block data were written and held in the buffer. When a write undo command is received from the controller, the block data in the buffer can be used to replace the overwritten portion of the block data, and thus the magnetic data that has been erroneously written can be used without adding a special mechanism. The tape can be restored.

[Brief description of the drawings]

FIG. 1 is a block diagram of a magnetic tape device according to a first embodiment of the present invention.

FIG. 2 is a flowchart of a write operation according to the first embodiment of the present invention.

FIG. 3 is a flowchart of a write cancel operation according to the first embodiment of the present invention.

FIG. 4 is a flowchart of a restoring operation of transferring to a higher-level device during a write cancel operation according to the first embodiment of the present invention.

FIG. 5 is a schematic diagram illustrating a recording state of a tape according to the first embodiment of the present invention.

FIG. 6 is a schematic diagram showing a storage state of a buffer according to the first embodiment of the present invention.

FIG. 7 is a block diagram of a magnetic tape device according to a third embodiment of the present invention.

FIG. 8 is a flowchart of a write operation according to the third embodiment of the present invention.

FIG. 9 is a schematic diagram illustrating a storage state of a buffer according to a third embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1, 20 Magnetic tape apparatus 2 Host apparatus 3 Buffer 4 Recording circuit 5 Reproduction circuit 6 Recording head 7, 14 Reproduction head 8 Drive circuit 9 Reel 10, 21 Tape drive 11 Control unit 12 Control means 13 Magnetic tape 14 Reproduction head 15 Reproduction circuit 16 Storage unit

Claims (6)

[Claims] 1. A buffer for temporarily storing a plurality of block data input from a host device during recording, and a buffer for transferring the stored block data to a host device during reproduction, and a block head for transferring the block data to a magnetic tape by a recording head. A tape drive for recording and reading the recorded block data from the magnetic tape by a reproducing head; and when receiving a command to read desired block data from the host device, the desired block data is stored in the buffer. Discriminates whether the block data is stored, and transfers the desired block data from the magnetic tape by controlling the tape drive when the block data is not stored. After transferring the desired block data to the higher-level device at the time when the block data is stored in the buffer, One or two or more block data subsequent to the desired block data are reproduced and sequentially stored in the buffer, and when a write command is received from the host device, the block data to be written is stored in the buffer. It is determined whether or not the data is stored, and the tape drive is controlled to reproduce a certain amount of data from the magnetic tape in the buffer including the block data to be written and one or more subsequent block data. Then, when a predetermined time has elapsed after the data is sequentially stored in the buffer or when a command that requires the buffer to be ejected is received, the data is read out, input to the tape drive and recorded on the magnetic tape, and the recording block is recorded. Control means for clearing data from the buffer. The control means, when receiving a write cancel command from the host device, when the first received block data of the write block data remains in the buffer, transfers the write block data to the magnetic tape. When the write reservation is cleared and the first received block data is not left in the buffer,
It is determined whether or not the first block data normally reproduced by reproducing the recording block data ahead of the write block data on the magnetic tape and the block data held in the buffer are continuous. When the data is read, the recording block data preceding the normally reproduced first block data on the magnetic tape is reproduced until a data end signal is detected, and written in the buffer. To position the recording head at the recording position immediately before the first received block data of the write data on the magnetic tape, and then record the recording block immediately before the first received block data from the recording position. And the reproduced and stored block data stored in the buffer in the order following the block data. Magnetic tape unit, characterized in that sequentially and Kudeta read from the buffer is recorded on the magnetic tape. 2. The control means reproduces recording block data preceding the normally reproduced first block data on the magnetic tape, writes the reproduced data in the buffer, and outputs the data end signal. When the reproduction data is written to the full capacity of the buffer without detecting the data, after transferring the block data in the buffer, the reproduction of the magnetic tape is continued until the data end signal is detected. After transferring the reproduced data to the higher-level device and allowing the higher-level device to perform a restoration process, the tape drive is controlled to cause the recording head to move the recording data to the first block data of the write data on the magnetic tape. After receiving the block data restored from the higher-level device after positioning at the recording position immediately before 2. The magnetic tape device according to claim 1, wherein the block data is recorded on the magnetic tape in order from the beginning. 3. A buffer for temporarily storing a plurality of block data input from a higher-level device during recording, and a buffer for transferring the stored block data to a higher-level device during reproduction, and a recording head for recording the block data on a magnetic tape. A tape drive for recording and reading the recorded block data from the magnetic tape by a reproducing head; and when receiving a command to read desired block data from the host device, the desired block data is stored in the buffer. Discriminates whether the block data is stored, and transfers the desired block data from the magnetic tape by controlling the tape drive when the block data is not stored. After transferring the desired block data to the higher-level device at the time when the block data is stored in the buffer, One or two or more block data subsequent to the desired block data are reproduced and sequentially stored in the buffer, and when a write command is received from the host device, the block data to be written is stored in the buffer. It is determined whether or not the data is stored, and the tape drive is controlled to reproduce a certain amount of data from the magnetic tape in the buffer including the block data to be written and one or more subsequent block data. Then, when a predetermined time has elapsed after the data is sequentially stored in the buffer or when a command that requires the buffer to be ejected is received, the data is read out, input to the tape drive and recorded on the magnetic tape, and the recording block is recorded. Control means for clearing data from the buffer. When receiving the write cancel command from the host device, the control unit checks whether the magnetic tape recording block data before being overwritten by the write block data remains in the buffer. While holding the block data in the buffer, after reproducing the block data from the beginning of the magnetic tape to immediately before the first received block data of the write block data and writing it in the buffer,
By controlling the tape drive, the recording head is positioned at a recording position on the magnetic tape immediately after the last-ordered block data in the buffer, and the block data in the buffer runs in the reverse order toward the beginning of the tape. A magnetic tape device for recording on a magnetic tape. 4. The control means reproduces block data from the beginning of the magnetic tape while retaining the block data in the buffer, and detects the reproduced data until the buffer capacity is full without detecting a data end signal. Is written, it is checked whether block data from the beginning of the magnetic tape to immediately before the first received block data of the write block data fits in the buffer, and if the block data fits in the buffer, the magnetic tape 4. The magnetic tape apparatus according to claim 3, wherein the block data from the beginning of the block data to the block data immediately before the first received block data among the write block data is reproduced and written in the buffer. 5. A buffer for temporarily storing a plurality of block data input from a host device during recording, and a buffer for transferring the stored block data to the host device during reproduction, and a recording head for recording the block data on a magnetic tape. A first read head reads and records the recorded block data from the magnetic tape, and a second read head disposed at a predetermined distance from the recording head upstream of the tape opposite to the first read head. A tape drive having a reproducing head of: when receiving a command to read desired block data from the higher-level device, determining whether or not the desired block data is stored in the buffer; The desired block data is transferred to the higher-level device, and when it is not stored, the tape drive is controlled to When the desired block data is reproduced from the magnetic tape and stored in the buffer, the desired block data is transferred to the host device, and then one or more block data subsequent to the desired block data is reproduced. Then, when a write command is received from the higher-level device, the block data in the buffer is cleared, and then the block data to be written is sequentially stored in the buffer for a fixed amount of the buffer. When a certain time has elapsed after the completion of the operation, or when a command that requires the buffer to be ejected is received, the data is read out, input to the tape drive and recorded on the magnetic tape, and the recording block data is cleared from the buffer. When the buffer runs out of free space, the recording head is moved to the highest position in the buffer. When positioning the block data in the order of writing to the tape recording start position, the second reproduction head reproduces the recording block data near the recording start position and writes it to the buffer, and then the recording head records the most At the same time, a fixed amount of block data read from the buffer is sequentially recorded on the magnetic tape from the block data in the order of writing first, and at the same time, the block data reproduced from the magnetic tape by the second reproducing head is written to the buffer. A magnetic tape device having control means, wherein the control means, when receiving a write cancel command from the higher-level device, when the first received block data of the write block data remains in the buffer. Write of the write block data to the magnetic tape If the first block data that has been received is cleared and the first received block data does not remain in the buffer, the first block data that has been normally reproduced by reproducing the recording block data preceding the write block data on the magnetic tape. And whether the block data held in the buffer is continuous or not, and when continuous, the recording block data ahead of the first block data normally reproduced on the magnetic tape, After the data is reproduced until the data end signal is detected and written into the buffer, the tape drive is controlled to control the recording head to record the data immediately before the first received block data among the write data on the magnetic tape. After positioning at the position, the recording block immediately before the first received block data from the recording position Ku magnetic tape unit, characterized in that the order the reading of the block data stored is the reproduction block data held in the buffer from the buffer in the order of recording on the magnetic tape. 6. The control means reproduces recording block data preceding the normally reproduced first block data on the magnetic tape, writes the reproduced data in the buffer, and outputs the data end signal. When the reproduced data is written to the full capacity of the buffer without detecting the data, the tape drive is controlled to move the recording head immediately before the first received block data of the write data on the magnetic tape. Then, after the block data in the buffer is sequentially recorded on the magnetic tape by a predetermined amount, the reproducing head is positioned immediately after the tape recording position of the last-ordered block data in the buffer. The magnetic tape is reproduced until a predetermined amount of block data is reproduced, and the reproduced block data is reproduced. 2. The magnetic tape device according to claim 1, wherein writing data to the buffer is repeated until the data end signal is detected.