JPH0485645A - Data transmission speed switching system - Google Patents

Abstract

PURPOSE:To prevent generating of the state of buffer full or buffer empty during data transmission by switching and controlling the data transmission speed with a channel device so as to be within the prescribed range based on the amount of data of the data buffer by command unit. CONSTITUTION:A data transmission speed switching means 18 is provided to switch the data transmission speed with an upper channel device to plural steps. At the time of the data transmission from the upper channel device 10 to an external storage device 14, as the amount of buffer data is increased, the transmission speed is switched to a low-speed side. At the time of data transmission from the external storage device 14 to the upper channel device 10, as the amount of the data buffer is increased, the transmission speed is switched to a high-speed side. Thus, the fluctuation of the amount of buffer data during transmission is restrained within the prescribed range, and the interruption of the transmission caused by the buffer full or the buffer empty is prevented.

Description

[Detailed description of the invention] 【overview】

The data transferred from the host channel device is compressed and stored in a data buffer before being transferred to an external storage device such as a magnetic tape storage device. On the other hand, the data transferred from the external storage device is stored in the data buffer and then decompressed and sent to the host. Regarding the transfer speed switching method of the data transfer control device that transfers data to the channel device, the purpose is to continue continuous data transfer without increasing the buffer capacity. As the amount of data increases, the transfer speed is switched to a lower speed. Conversely, when transferring data from an external storage device to an upper channel device, as the amount of buffered data increases, the transfer speed is switched to a higher speed. The configuration is such that fluctuations in the data are suppressed within a predetermined range to avoid interruption of transfer due to buffer full or buffer fullness.

[Industrial application field]

The present invention compresses the data transferred from the host side and then transfers the data to and from an external storage device such as a magnetic tape device with a channel device on the host side.
The present invention relates to a data transfer speed switching system in which transfer data from an external storage device is stored in a data buffer and then decompressed and transferred. In data transfer between the host-side channel device and the magnetic tape controller installed in the magnetic tape device (1), the transfer data (write data) from the channel device is compressed into a predetermined signal format, and then transferred via the data buffer. L2 transfer j7
After receiving the transfer data (read data) from the magnetic wave device in the buffer, it is decompressed and transferred to the channel device side. However, since the data is compressed or expanded (j9) and then transferred (d), there is a difference between the amount of received data and the small amount of data sent.・I have set up a data buffer, but there is a small amount of γ required for compression and decompression.
During transfer, 1. This causes a buffer full or buffer block 2, which causes data transfer to be interrupted and the magnetic tape device to stop streaming (stopping continuous processing). This problem can be solved by increasing the buffer r capacity, but increasing the capacity will increase the memory space of the host used for recovery processing in the event of an error. Therefore, without increasing the data buffer capacity, , 8 continuous transfer is desired.

[Prior Art] Conventionally, in data transfer control by a magnetic tape control device 100 installed between a =f Yarnel device 10 on the host side and a magnetic tape device 14 as an external storage device shown in FIG. , receives commands from channel device rR,io1
．． 1. Also, under the control of the command control unit 30, write data from the channel device 10 to the magnetic tape device 1-4 is transferred to the data transfer control unit 32 in the magnetic tape control device 100 (sequentially provided data The compression/expansion circuit 22 compresses the signal into a predetermined signal format, and later transfers the signal via the data buffer 16. Also, the magnetic tape device 14
The read data from is first stored in the data buffer 16 of the magnetic tape control device 100, then decompressed by the data compression/decompression circuit 22, and transferred to the channel device 10 by the data transfer control section 32. In data transfer that involves compression or expansion of data, for example, in compressed transfer of write data, the amount of transmitted data is reduced by compression compared to the amount of received data, and in decompressed transfer of read data, the amount of received data is However, the amount of transmitted data increases due to expansion, and in order to absorb this difference in the amount of transmitted and received data, a data buffer 16 is provided in the magnetic tape control unit FIT 1.00 to interrupt data transfer and prevent it from occurring. There is. [Problems to be Solved by the Invention] However, the received i! - When the difference between the data amount and the amount of data to be transmitted becomes large, the data cannot be absorbed completely in the i'-ta buffer 6, and a buffer full or buffer emboggy state occurs. Interruption or streaming stop of the magnetic tape device 14 may occur, and data transfer may take a long time (7 minutes).In order to solve this problem, it is possible to increase the capacity of the data buffer I6, but This causes a problem in the recovery process when a write error occurs.In other words, the host side reserves a memory area equal to the data buffer capacity for the recovery process when a write error occurs, and the unwritten data in the data buffer 1.6 is saved. data is transferred to the corresponding memory area so that the data can be transferred again during recovery processing when an error occurs.As a result, as the capacity of the data buffer increases, the memory area for recovery on the host side increases, and the recovery processing also takes longer. The present invention was made in view of such conventional problems, and aims to provide a data transfer rate switching method that allows continuous data transfer without increasing the buffer capacity. [Means for Solving the Problems] Fig. 1 is a diagram explaining the principle of the present invention. First, the present invention compresses transfer data from an upper channel device 10 and stores it in a data buffer 16. Afterwards, the data is transferred to an external storage device 14, for example, a magnetic tape device.
The present invention is directed to a data transfer rate switching system for a data transfer control device that stores transfer data from an external storage device 1-4 in a data buffer 1G, decompresses it, and transfers it to a channel device 10. That is, in the data transfer rate switching method of the present invention, there is a data transfer rate switching stage 1, 8 that switches the data transfer rate between the upper channel device 10 and the external storage device in a plurality of stages, and When transferring data to the external storage device 14, as the amount of data in the buffer increases, the transfer speed is switched to a lower speed side.
・＼r・-Control means for switching to a higher transfer speed as the number of sunset scenes increases during evening transfer] 8. For example, the control means 18 switches the data transfer speed to three levels: low speed, medium speed, and high speed, depending on the amount of data buffer.

[Effect]

According to the data transfer rate switching method of the present invention having such a configuration, switching control is performed for each command based on the amount of data in the data buffer so that the data transfer rate with the channel device is within a predetermined range. without increasing the data buffer capacity, ensuring that a buffer full or empty state does not occur during data transfer, interrupting data transfer with a channel device, or stopping streaming of a magnetic tape device. can be prevented.

【Example】

FIG. 2 is a block diagram showing an embodiment of the present invention. In Figure 2, Otsu 1-0 is the channel device on the host side, 1
4 is a magnetic tape device as an external storage device, and a magnetic tape control device 100 is provided between the channel device 10 and the magnetic tape device 14 as a data transfer control device for transferring data between the two. The magnetic tape control device 100 includes a data transfer rate switching unit 1.
8 is provided, and in this embodiment, the channel device 1
A low-speed data transfer control unit 341 and a channel device 10 with a data transfer rate of 1°5 MB/S between
A medium-speed data transfer control unit 34-2 that has a data transfer rate of 3.0MB/S with the channel device and a high-speed data transfer control unit that has a data transfer rate of 4.5MB/S with the channel device mio. 34-3 are provided, and these data transfer control units 34-1 to 34-3 are switched and selected by a data transfer rate switching circuit 36. A data compression/expansion circuit 22 is provided following the data transfer rate switching circuit 36, which compresses write data from the channel device 10 to the magnetic tape device 14 into a predetermined signal format, and conversely compresses write data from the magnetic tape device 14 to the channel device 10. Extend read data. A data buffer 16 is provided following the data compression/expansion circuit 22, and write data or read data is exchanged between the data buffer 1-6 and the magnetic tape device 14. Each circuit of the data transfer system provided in the magnetic tape control device 100 is controlled by the command control section 20. An appropriate access command is given to the command control section 20 from the channel device 10, and the command control section 20 decodes this access command and outputs a control signal to the magnetic tape device 14. Further, the command control section 20 instructs the data compression/expansion circuit 22 to perform a data compression operation when transferring write data, and on the other hand, instructs a data expansion operation when transferring write data. Furthermore, the command control section 20 has a function as a control means for switching and controlling the data transfer rate with the channel device 10 according to the amount of data in the data buffer 16. In this embodiment, as shown in FIG. 3(a), the data buffer 16 is set with two data amount threshold levels, a lower level and an upper level, and the diagonal lines stored in the data buffer 16 are The command control unit 20 compares the data amount indicated by the lower level and the upper level and sends the lower level detection signal and the upper level detection signal without indicating whether the data amount has reached the lower level or upper level.
5. In this way, the command control unit 20 switches the data transfer speed as shown in FIG. 3(b) for the lower level and upper level set in the data buffer 16. That is, at the time of writing, in which data from the channel device 10 is compressed and transferred to the magnetic tape device @14, if the amount of data in the data buffer 16 is less than the lower level, the transfer rate is the highest, 4.5 MB/S. Switching, if lower level or higher and lower than upper level, middle 3.0MB/S
, and further switches to a data transfer rate of 5 MB/S, which is the slowest for upper level and above. On the other hand, when read data from the magnetic tape device 14 is decompressed and transferred to the channel device 1-0, the slowest speed is 1.5MB/S when the data is below the lower level.
When the data transfer rate is higher than the lower level and lower than the upper level, the data transfer rate is set to 3. The data transfer rate is set to QMB/S, and when the level is lower than the upper level, the data transfer rate is switched to the fastest data transfer rate of 4.5MB/S. The correspondence between the amount of data in the data buffer 16 and the transfer speed shown in FIG.
- is realized by the command control unit 20 executing. Next, the operation of the embodiment shown in FIG. 2 will be explained. Now, if a write command is issued from the channel device 10 to the command control unit 20 of the magnetic tape control device 100, the command control unit 20 outputs a control signal for a write operation to the magnetic tape device 14 by analyzing the command.
At the same time, the data compression/expansion circuit 20 is brought into a data compression operating state. At the start of transfer when the data buffer 16 is empty, the command control unit 20 sets the data transfer rate switching circuit 36 to, for example, a data transfer rate of 3.0 MB/
A command is given to switch to S, and the transfer of write data using the data transfer control unit 34-2 is started. Channel device 1
The write data transferred from the data transfer controller 10 to the data transfer controller 34-2 at a rate of 3.0 MB/S is compressed by the data compression/expansion circuit 22 via the data transfer rate switching circuit 36, and sequentially stored in the data buffer 16. . Command control unit 2
0 monitors whether the amount of data stored in the data buffer 16 has reached, for example, a lower level, and when the amount of data reaches the lower level, starts transferring write data from the data buffer 16 to the magnetic tape device 14. During such write data transfer, for example, if the amount of compressed data stored by the data compression/expansion circuit 22 becomes larger than the amount of data sent out from the data buffer 16, the amount of data in the data buffer 1.6 becomes larger. Gradually increases to exceed upper level. data buffer 1
When the data amount of 1.6 exceeds the upper level, the command control unit 20 causes the data transfer rate switching circuit 36 to switch to a lower data transfer rate of 1.6. ．． Instruct to switch to 5MB/S 7,
The data transfer control unit 34-1 is selected, and the channel device 1
The data transfer speed from 0 to 0 has been reduced to 1.5 MB/S, which is half of the previous 3.0 MB/S. Therefore, the amount of data input from the data compression/expansion circuit 22 to the data buffer 16 decreases, and the amount of data exceeding the upper level gradually decreases to fall between the upper level and the lower level. Conversely, when the amount of data from the data compression/expansion circuit 22 becomes smaller than the amount of data transferred from the data buffer 16, the amount of data in the data buffer J6 gradually decreases and becomes below the lower level. When the amount of data falls below the lower level, the command control unit 20 controls the data transfer rate switching circuit 36 to prevent the amount of data from decreasing further.
Faster data transfer rate of 4°5 MB/
2, and the data transfer control unit 34-3
becomes effective, and the reduced data amount will be recovered between the lower and upper levels. The data buffer 1 by such a command control unit 20
The switching of the data transfer rate with the channel device 10 based on the data amount of 6 is performed by switching the transfer rate based on the data amount of the data buffer 16 for each command. Therefore, when transferring write data, the amount of data in the data buffer ]-6 falls between the lower level and the upper level, and the buffer becomes full during data transfer, causing data transfer from the channel device 10 to be interrupted. It is possible to reliably prevent the magnetic tape device 14 from causing a streaming stop due to the buffer becoming empty. On the other hand, when reading, contrary to when writing, the larger the amount of data in the data buffer 16, the more the channel device "0"
Switch the data transfer rate to a higher rate. In other words, 3. with an intermediate data transfer rate. When the amount of data in the data buffer 16 decreases to below the lower level in the OMB/S state, 1. ! Switching to the data transfer control unit 14-1 having a data transfer rate of 5 MB/S suppresses a decrease in the amount of data in the data buffer 16. Conversely, when the amount of data in the data buffer 16 increases and exceeds the upper level, the data transfer rate increases from 3.0 MB/S to 4.
．． Switch to 5 MB/S, data buffer 1, 6
control the increase in the amount of data. Therefore, even during reading, the amount of data in the data buffer 1G is kept within the range between the lower level and the upper level, preventing the data buffer 16 from becoming full or empty. Interruption of data transfer or streaming stop of the magnetic tape device 1-4 can be prevented. The above embodiment takes as an example the case where the data transfer speed with the channel device "0" is switched to three stages: low speed, medium speed, and high speed, but it can be changed to two stages or four stages or more as necessary. The number of switching stages may be set as appropriate. Of course, the numerical values of the transfer speed in the three-stage embodiment described above are merely an example, and the present invention is not limited thereto. [Effects of the Invention] As explained above, according to the present invention, the data transfer rate can be changed according to the amount of data in the data buffer without increasing the capacity of the data buffer, so that the buffer is full or not during data transfer. Interruption of data transfer due to empty buffers or streaming stop when using a magnetic tape device as an external storage device can be prevented, and data transfer efficiency can be improved.

[Brief explanation of the drawing]

Fig. 1 is a diagram explaining the principle of the present invention; Fig. 2 is a configuration diagram of an embodiment of the present invention; Fig. 3 is a correspondence diagram of the buffer data amount and transfer rate of the present invention; Fig. 4 is a transfer rate switching diagram of the present invention. Flowchart; FIG. 5 is a block diagram of the conventional system. In the figure, 14:16:1.8:20. 22: 36: Upper channel device (channel device) External storage device (magnetic tape device) Data buffer transfer speed switching means control means (command control section) Data compression/expansion circuits 1 to 34-3: Data transfer control section Data transfer speed switching circuit

Claims (2)

[Claims] (1) The transfer data from the upper channel device (10) is compressed and stored in the data buffer (16), and then transferred to the external storage device (14), while the transfer data from the external storage device (14) is compressed and stored in the data buffer (16). In a data transfer control device that stores data in a data buffer (16), decompresses it, and transfers it to the upper channel device (10), the data transfer rate with the upper channel device (10) is switched to multiple stages. Transfer speed switching means (18)
When transferring data from the upper channel device (10) to the external storage device (14), as the amount of buffered data increases, the transfer speed is switched to a lower speed side, and the transfer speed is switched from the external storage device (14) to the upper channel device (10). 1. A data transfer rate switching system comprising: a control means (18) for switching to a higher transfer rate as the amount of buffered data increases during data transfer to; (2) The data transfer rate switching system according to claim 1, wherein the control means (18) switches the data transfer rate into three stages: low speed, medium speed, and high speed, depending on the amount of data buffer.