JPH0511927A - Data reproducing method for magnetic tape unit - Google Patents

Abstract

PURPOSE:To transmit reversely read data to a host by reversely reading the compressed data stored on a magnetic tape even when reverse restorage is disabled by a compression algorithm or the like. CONSTITUTION:A data buffer 8 stores the (reverse) data read out of the magnetic tape by reversely traveling the tape, the (forward) data are reversely read out of the data buffer 8, the read data are restored at a data compression/ restorage circuit 2, the restored data are stored in a data buffer 5, and the (reverse) data are reversely read out of the data buffer 5 and transferred to the host.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a data reproducing method for a magnetic tape device, and in particular, in a magnetic tape device which cannot be restored by backward feeding of the magnetic tape due to a compression algorithm, the data is stored on the magnetic tape. It is possible to read the compressed data in the reverse direction and send the read data in the reverse direction to the host, thereby making it possible to use the program having the conventional reverse read instruction as it is. The present invention relates to a data reproducing method.

[0002]

2. Description of the Related Art As conventional data compression / decompression methods,
As described in JP-B-63-6172,
A method is known in which only one-way decompression is possible when decompressing compressed data.

In addition, American National Standard Extended Magnetic Tape Format Information Informatics EX 3B-5 / 89-201M (AMERIC)
AN NATIONAL STANDARD EXTEN
DED MAGNETIC TAPE FORMAT
FOR INFORMATION INTERCHAN
GE X3B5 / 89-201M), one group of data transferred from the host is compressed in the forward direction by the above-described data compression technique capable of only one-way decompression. One packet is defined and a plurality of packets are concatenated to form one data block, which is recorded on the magnetic tape. further,
When the recorded data is read in the forward direction for each group, all one data block on the magnetic tape is recorded in the buffer for temporary recording, and then the start position of the required packet and its The end position of the data in the packet is detected, the data in the packet is read from the buffer for temporary recording, the compressed data is restored, and one packet of data is transferred to the host.

[0004]

DISCLOSURE OF THE INVENTION In the prior art,
As described above, it is impossible to restore in the backward direction due to the compression algorithm. Therefore, the compressed data stored on the magnetic tape cannot be read out and restored by the backward feeding of the magnetic tape. Therefore, when the backward read command is output from the host, an error message is sent to the host side, and the forward read command is reissued as a recovery by the operating system (hereinafter referred to as OS).

When the forward direction read command is reissued, the position of the data block on the magnetic tape at which the reading is started is different from that in the backward direction reading. Therefore, positioning is performed again, and then the forward direction reading is performed. For this reason,
There is a problem that it takes a lot of time until the data reading is completed and the overhead on the host side increases.

[0006] Further, the above-mentioned American National Standard Extended Magnetic Tape Format Information Information Intake Engineering 3B-5 / 89-201M (A
MERICA NATIONAL STANDARD
EXTENDED MAGNETIC TAPE F
ORMAT FOR INFORMATION INTO
In the technology described in ERCHANGEX3B5 / 89-201M), when the data in the packet is recorded on the magnetic tape without being compressed, the data stored on the magnetic tape is read by the backward feeding of the magnetic tape, and this is read. It could not be directly transferred to the host side. The reason is that, since no gap area is provided between each packet, the beginning and end of the data in each packet are unknown even in the uncompressed data.

The present invention has been made in view of the above-mentioned problems of the prior art. Even when backward compression cannot be performed due to the compression algorithm, the compressed data stored on the magnetic tape is reversed. Read data to the host and send the read data in the reverse direction to the host, which allows the conventional program to be used as it is and further reduces the load on the host side for the reverse direction read instruction (no error recovery by the OS is required). It is an object of the present invention to provide a data reproducing method of a magnetic tape device capable of realizing the above.

Still another object of the present invention is to read the uncompressed data stored on the magnetic tape in the reverse direction when recording a plurality of packets of the non-compressed data as one data block. Another object of the present invention is to provide a data reproducing method of a magnetic tape device, which makes it possible to transmit the read data of the above to the host.

[0009]

According to a first aspect of the present invention, there is provided a data reproducing method for a magnetic tape device, comprising data compression / decompression means for compressing one group of data transferred from a host into one packet, Multiple packets are concatenated in a chain to form one data block, which is recorded on the magnetic tape in units of one data block, and when the recorded data is reproduced, the data read from the magnetic tape is restored and transferred to the host. And a first step of reversing the transfer order of the data read from the magnetic tape in the state where the magnetic tape is run in the reverse direction. A second step of restoring the data whose transfer order has been reversed, and a third step of reversing the transfer order of the data restored in the second step.
And the steps of.

A second data reproducing method for a magnetic tape device of the present invention comprises a data compression / decompression means, compresses one group of data transferred from the host into one packet, and the one packet is at least the tape. It is configured to have its own position above and control information indicating a storage area in the packet of the above data and data transferred from the host, and a plurality of packets are concatenated in a chain to form one data block and one data. It is applied to a magnetic tape device that records on a magnetic tape in blocks and reproduces the recorded data by restoring the data in the target packet of the data read from the magnetic tape and transferring it to the host. The first step of storing the data read from the magnetic tape, particularly when the magnetic tape is running in the opposite direction. A second step of determining whether the purpose of the packet by reading a control information packet in the stored data in the first step, if it is determined that the packet of interest in a second step,
The third step of knowing the start position and the end position of the data in the packet from the control information, and reading and transferring the data in the target packet in the reverse direction from the final position to the start position based on this. A fourth step of restoring the data in the packet of interest transferred in the third step, a fourth step of storing the data in the packet of interest restored in the fourth step, In the fourth step, the data stored in the fourth step is read in the reverse direction and transferred to the host.

According to the third data reproducing method of the magnetic tape device of the present invention, one group of data transferred from the host is regarded as one packet, and the one packet is at least the position on the tape and the packet of the data. In the storage area and control data indicating the storage area, and data transferred from the host. A plurality of packets are concatenated in a chain without a gap area to form one data block. It is applied to a magnetic tape device that transfers the data in the target packet of the data read from the magnetic tape to the host when recording the data on the magnetic tape and reproducing the recorded data. With the tape running in the reverse direction, the first step of storing the data read from the magnetic tape and the first step of storing the data read from the magnetic tape. In the second step, the control information of the packet in the data stored in the packet is read to determine whether or not the packet is the target packet, and when it is determined that the packet is the target packet in the second step, A third step of knowing the start position and the end position of the data in the packet, and reading and transferring the data in the target packet in the reverse direction from the final position to the start position based on this Storing the data in the packet of interest transferred in step 4;
And the fifth step of reading the data stored in the fourth step in the reverse direction and transferring it to the host.

[0012]

According to the first and second aspects of the present invention, the compressed data stored on the magnetic tape is read in the reverse direction even when the reverse direction cannot be restored due to the compression algorithm of the magnetic tape device. The data transfer order can be reversed to restore the data, and the restored data transfer order can be reversed and sent to the host. Therefore, it becomes possible to send read data in the reverse direction to the host,
As a result, the conventional program can be used as it is, and the load on the host side for the backward read instruction can be reduced (no error recovery by the OS is required). Further, according to the third aspect of the invention, when a plurality of packets of uncompressed data are recorded on the magnetic tape as one data block, the uncompressed data stored on the magnetic tape is reversed. Read and store, know the start position and end position of the data in each packet from the control information of each packet, transfer the data from the end position to the start position, store the transferred data, and store in the reverse direction. By reading, it becomes possible to read the uncompressed data stored on the magnetic tape in the reverse direction, and to send the read data in the reverse direction to the host.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. FIG. 2 shows the data format on the magnetic tape when the data sent from the host is recorded on the magnetic tape.

In FIG. 2, standard data format 1
00 does not perform data compression and records one group of data transferred from the host as one data block on the magnetic tape. At this time, by inserting a gap called IBG between the data blocks, the start end and the end of one data block can be known.

The data format 101 shown in FIG.
The object of the present invention is to compress the data transferred from the host to reduce the data amount.
Let it be a packet. Furthermore, 1 recorded on the magnetic tape
The data block is composed of a plurality of (n) packets connected to each other. That is, as shown in the figure, the IBG is deleted until the information reaches a predetermined fixed amount, and the packets are connected to form one data block 107 from one packet to n packets.

Each packet 102 is composed of a packet ID 103, user data 104, and a packet trailer 105, as shown in the figure. Where packet ID
Reference numeral 103 is composed of 32 bytes, and is recorded in an uncompressed state at the beginning of the packet. This packet ID 103
Indicates a block ID indicating the block position of a block included in the packet, a packet offset position 106 indicating the total number of bytes obtained by adding the number of bytes of the packet ID 103 and the number of bytes of the user data 104, and the packet trailer 105. It is composed of information indicating the number of bytes and 2 bytes of redundant information for the preceding 30 bytes in the packet ID 103.

The user data 104 is an area for recording data obtained by compressing the data transferred from the host or uncompressed data. This embodiment shows the case of compressed data.

The packet trailer 105 includes the number of bytes of uncompressed data transferred from the host, redundancy information CRC1 for the data, and user data 1 after compression.
Redundancy information CRC2 including 04 bytes and CRC1
And information to which padding data “00” is added so that the total byte length of the user data 104 and the packet trailer 105 is a multiple of 32, and the compressed user data 1
04 information and redundant information CRC3 including the information of the packet trailer 105.

FIG. 1 is a block diagram showing an embodiment of the present invention. First, the operation of writing data on a magnetic tape will be described. In FIG. 1, the data transferred from the host is input to the data compression / decompression circuit 2 via the channel interface 1 and compressed in the data compression / decompression circuit. The compressed data is stored in the main data buffer 4 via the data buffer interface 3 as the user data 104 in the packet. Then, the information of the packet trailer 105 from the data compression / decompression circuit 2 is stored in the main data buffer 4 via the data buffer interface 3. A user·
After the data 104 and the data of the packet trailer 105 are stored in the main data back 4, the microprocessor 9 causes the packet ID 103
Information is generated and transferred to the write PID register 6.
The transferred packet ID information is added with a redundant information byte CRC2 at the end and stored in the main data buffer 4 via the data buffer interface 3. After that,
By repeating the same operation, a plurality of packets are stored in the main data buffer.

When the total number of bytes of the packets stored in the main data buffer 4 reaches a constant value, the plurality of packets stored up to that point constitute one data block and the data format 101 and packet 10 after data compression shown in FIG.
Data is recorded on the magnetic tape in the order of the structure shown in 2.

Next, the backward data restoring operation will be described. Here, it is assumed that the data compression / decompression circuit 2 cannot perform backward decompression. Even in this case, the data buffer 8 makes the direction of the data forward so that the restoration operation can be performed.

That is, when the host reads the user data 104 of the first packet in the reverse direction, one data block 1 containing one packet required on the magnetic tape.
The information 07 is stored in the main data buffer 4 by running the magnetic tape in the reverse direction.

When the information of one data block 107 is stored in the main data buffer 4, the microprocessor 9
The signal line 10 instructs to transfer data from the main data buffer 4 to the data buffer 8 via the data buffer interface 3. As a result, the data stored in the main data buffer 4 is transferred to and stored in the data buffer 8.

Since the information of one data block 107 stored in the data buffer 8 is read and stored in the reverse direction, its address is sequentially counted up from the end of n packets, and finally one packet. End of the packet ID 103. Therefore, in order to read one packet of user data 104 from the data buffer 8 in the forward direction, the microprocessor 9 sets the data buffer 8 to count down the address of the data buffer 8 by the signal line 11 and stores it in the data buffer 8. Counting down from the final address of the 1 data block 107 that has been performed, the packet ID 103
Information in the forward direction is transferred to the read PID register 7.

The microprocessor 9 analyzes the information of the packet ID 103 in the read PID register 7 to determine whether it is the target packet and the offset position 106 of the packet. Next, in the case of the target packet, in order to transfer the user data 104 in one packet to the host, the address obtained by subtracting 32 bytes of the packet ID from the final address of the data buffer 8 is sent from the microprocessor 9. The data is set in the data buffer 8 by the bus line 12 and used as the start address of the user data 104. As the end of the user data 104 in one packet, the address of the offset position 106 of the packet is set in the data buffer 8 by the bus line 12 from the microprocessor 9 as described above. The signal line 13 instructs the microprocessor 9 to read out data in a countdown from the start address to the end address of the data buffer 8.
When output by, one packet of user data 14 is
The data is transferred from the data buffer 8 to the data compression / decompression circuit 2, and the forward data decompression operation is performed.

Data decompressed in the forward direction is stored in the data buffer 5 by the data compression / decompression circuit 2 with the address counted up.

When the data compression / decompression circuit 2 completes the data decompression of one packet of user data 104, an end signal is sent to the data buffer 5 by the signal line 13, whereby the data buffer 5 switches the address count to the countdown. . Then, the data buffer 5
All the restored user data 104 stored in (1) are transferred from the data buffer 5 to the host side via the channel interface 1 by updating the address by the countdown. At this time, the data transferred to the host is transferred in the reverse direction to that when the data was written in the normal direction from the host, and the reverse direction reading is performed.

Next, the host sends 2 in 1 data block.
When an instruction is issued to read the user data of the packet in the reverse direction, all the data of one data block has already been stored in the data buffer 8, so it is possible to read it without operating the magnetic tape. . That is, as in the case described above, the microprocessor 9 searches the packet ID 103 for the beginning of the packet ID of the second packet, and transfers the user data 104 of the second packet to the host side by the reverse transfer as in the above case. .

As is apparent from the above description, according to the above embodiment, even if the data compression / decompression circuit is a compression / decompression system capable of decompression operation in only one direction, a backward read command from the host is used. Can be realized.

Further, in the data writing method in which a plurality of packets are concatenated into one data block, when packets in the same data block are successively read in the reverse direction,
By combining with the data restoration method, data restoration and reverse reading can be performed without operating the magnetic tape. Therefore, the overhead of the host can be reduced, and the processing time at the time of reverse reading can be shortened.

In the above embodiment, the case where the data sent from the host is compressed by the data compression / decompression circuit and recorded on the magnetic tape has been described, but the present invention is not limited to this. As shown in the reference data format 100 of FIG. 2, the present invention can also be applied to the case of recording uncompressed data on a magnetic tape.

In the above embodiment, as shown in the data format 101 after compression shown in FIG. 2, an example in which no gap IBG is provided between packets is shown, but the present invention is not limited to this. However, a gap IBG may be provided between each packet. In this case, if a predetermined number of packets are read from the magnetic tape and the reading from the magnetic tape is stopped, the read packet group may be set as one data block.

[0033]

According to the present invention, the compressed data stored on the magnetic tape is read in the reverse direction and the read data in the reverse direction is read even if the reverse direction cannot be restored due to the compression algorithm. It is possible to send the data to the host, and thus the conventional program can be used as it is, and further, the load on the host side for the backward read instruction can be reduced (no error recovery by the OS is required). The processing time can be shortened.

Furthermore, according to the present invention, when a plurality of packets of uncompressed data are recorded as one data block, the uncompressed data stored on the magnetic tape is read in the reverse direction and read in the reverse direction. It is possible to provide a data reproducing method of a magnetic tape device that enables data to be transmitted to a host.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a magnetic tape device of the present invention.

FIG. 2 is a diagram showing an example of a data format of data recorded on a magnetic tape.

[Explanation of symbols]

1 ... Channel interface, 2 ... Data compression / decompression circuit, 3 ... Data buffer interface, 4 ... Main data buffer, 5 ... Data buffer, 6 ... Write PID
Register, 7 ... Read PID register, 8 ... Data buffer, 9 ... Microprocessor, 100 ... Standard data format, 101 ... Data format after data compression, 102 ... Packet, 103 ... Packet ID, 104
... user data, 105 ... packet trailer, 106 ...
Offset position of packet, 107 ... 1 data block.

Claims (3)

[Claims] 1. A data compression / decompression means is provided for compressing one group of data transferred from a host into one packet, and connecting a plurality of packets in a chain to form one data block, one data block unit. On a magnetic tape,
In a magnetic tape device that restores the data read from the magnetic tape and transfers it to the host when playing back the recorded data, the data read from the magnetic tape when the magnetic tape is running in the reverse direction. First to reverse the transfer order of
Step, the second step of restoring the data whose transfer order has been reversed in the first step, and the third step of reversing the transfer order of the data restored in the second step and transferring it to the host. And a data reproducing method in a magnetic tape device. 2. A data compression / decompression means is provided to compress one group of data transferred from the host into one packet, and the one packet stores at least its position on the tape and the data in the packet. It is configured to have control information indicating an area and data transferred from the host. A plurality of packets are concatenated in a chain to form one data block, which is recorded on a magnetic tape in units of one data block. When reproducing, in a magnetic tape device that restores the data in the target packet of the data read from the magnetic tape and transfers it to the host, when the magnetic tape is running in the reverse direction, The first step of storing the read data and the control information of the packet in the data stored in the first step The second step of deciding whether or not the packet is a target packet, and when it is determined to be the target packet in the second step, the start position and the final position of the data in the packet are known from the control information. A third step of reading the data in the target packet in the reverse direction from the final position to the start position based on this, and transferring the data; and the data in the target packet transferred in the third step. And a fourth step of storing the data in the packet of interest restored in the fourth step, and reading the data stored in the fourth step in the reverse direction to the host. A data reproducing method in a magnetic tape device, which comprises a fifth step of transferring. 3. One group of data transferred from the host is defined as one packet, and the one packet is transferred from the host and at least control information indicating a position on the tape and a storage area of the data in the packet. When a plurality of packets are connected in a chain without a gap area to form one data block and recorded on a magnetic tape in units of one data block, and the recorded data is reproduced, In a magnetic tape device that transfers the data in the target packet of the data read from the magnetic tape to the host, the data read from the magnetic tape is stored while the magnetic tape is running in the reverse direction. The first step and reading the control information of the packet in the data stored in the first step If it is determined that the packet is the target packet in the second step of determining whether the packet is a packet or not, the start position and the final position of the data in the packet are known from the control information, and based on this, A third step of reading and transferring the data in the target packet in the reverse direction from the final position to the head position, and a fourth step of storing the data in the target packet transferred in the third step. And a fifth step of reading the data stored in the fourth step in the reverse direction and transferring it to the host, the data reproducing method in the magnetic tape device.