JPH0612188A - Data transfer control system for external storage controller - Google Patents

Abstract

PURPOSE:To minimize a connecting time with a host device by adding the element of a command chain time and a reconnecting time to the data processing time at the host device side, and deciding data quantity to be read at first by considering the data processing time of an external storage device. CONSTITUTION:A magnetic disk controller 1 is connected through a channel port 2 with the host device, and recognizes which channel port generates an activation from an activation detecting circuit 3. A microprocessor 4 which mainly controls a data trasfer at the host device side is connected through a bus line 6 with a microprocessor 5 which mainly controls the data trasfer at a slave device side. At the time of operating the data trasfer between a disk volume 10 and the host device, the microprocessor 4 selects the microprocessor 5. A buffer 7 stores the data to be read and written in the disk volume 10 by the microprocessor 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a data transfer control system for an external storage control device, and more particularly, by optimizing a data read-ahead amount when transferring data from an external storage device to a host device, By minimizing the time to stay in the data buffer in the external storage controller, the host device,
The present invention relates to a data transfer control method for improving the throughput of an external storage control device.

[0002]

2. Description of the Related Art In data transfer between a host device and an external storage device, data is stored in an external storage control device that controls the external storage device in order to absorb a difference in data transfer capability between the host device and the external storage device. It is common practice to provide a buffer and transfer data via the data buffer. In particular, if the data transfer capacity of the external storage device is significantly smaller than that of the host device, start the data transfer between the external storage device and the external storage control device before starting the data transfer with the host device. Then, the transfer data is stored in the data buffer, so-called data prefetching is performed.

As a technique related to this data prefetching, for example, in the technique disclosed in Japanese Patent Laid-Open No. 62-92022, data transfer is performed when the data transfer rate on the host device side is higher than the data transfer rate on the external storage control device side. There is a means for prefetching for the amount x data transfer rate ratio.

The time required for data transfer is the data transfer amount /
Since it is determined by the data transfer rate, in order to minimize the data transfer time between the host device and the external storage controller, the total amount of data to be transferred must be set to the ratio of the data transfer rate of the external storage device to the data transfer rate of the host device. It is the most rational to use the multiplied data amount as the read-ahead data amount.

However, in recent years, an optical fiber or the like may be used as an interface for connecting a higher-level device and an external storage control device, and the cable length can be remarkably extended as compared with the conventionally used metal cable. It is possible.

For this reason, the influence of the cable length of the interface cannot be neglected in the command chain time and the reconnection time with the host device, which are considered to be almost fixed in the past.

Since a plurality of commands are usually chained in an input / output command from a host device, it is necessary to take the command chain time into consideration when calculating the data transfer time.

In other words, the technique disclosed in the above publication may not be able to optimize the amount of data to be read in advance in such a situation, and the purpose of minimizing the connection time with the host device cannot be achieved. There was a problem.

Further, there is a problem that the above technique cannot deal with the case where the amount of data processing is large and the amount of data that can be read in advance is limited by the capacity of the data buffer in the control device.

[0010]

In view of the above problems, the present invention considers the data processing time on the external storage device side by adding the command chain time and the reconnection time to the data processing time on the host device side. By determining the amount of data to be read ahead by comparing, even under the above-mentioned situation,
It is to provide a means by which the original purpose can be achieved.

[0011]

SUMMARY OF THE INVENTION An object of the present invention is to determine the amount of data read ahead by comparing the data processing time on the host device side with the data transfer time on the external storage device side before starting data transfer. This is achieved by providing a means for predicting a shortage of the prefetch amount from the data transfer amount. The purpose is to measure the command chain time in the command before the start of data transfer, a means for giving the data transfer rate of the host device and the external storage device as preset information, and a response from issuing a connection request to the host device. Is realized by means for measuring the time, and means for determining the amount of prefetching of combined data of these pieces of information.

[0012]

The command chain used for data input / output must be at least before the command to start data transfer.
It is necessary to include specific and at least two commands, and to be provided with information for measuring the command chain time and determining the data transfer amount.

For example, in the case of a magnetic disk controller, since the DEFINE EXTENT command and the LOCATE RECORD command are issued before the start of data transfer, the command chain time can be measured. Since the length is given, it is possible to predict the data transfer amount.

The command chain time is almost constant and does not depend on the type of command. In addition, the data transfer rate on the host device side is often set as the configuration information of the external storage control device at the time of installation. The transfer rate of the external storage device, the data buffer capacity, and the like can be given as preset information.

The time required for reconnection to the host device is
Although it may vary depending on the load status of the host device, it is possible to predict the approximate time by having the past history information.

If the above information can be obtained, an accurate data processing time can be obtained. Therefore, the amount of read-ahead data can be calculated according to the data transfer capabilities of the host device side and the external storage device side. .

[0017]

Embodiments of the present invention will be described with reference to a magnetic disk subsystem.

FIG. 1 is a block diagram showing an example of a computer system constructed by using a magnetic disk subsystem which is an embodiment of the present invention. In FIG. 1, the magnetic disk control device 1 is connected to a host device through a channel port 2, and the activation detection circuit 3 can know from which channel port the activation came. The microprocessor 4 which mainly controls the data transfer on the upper device side and the microprocessor 5 which mainly controls the data transfer on the lower device side are connected by a bus line 6, and the data between the disk volume 10 and the upper device is connected. When transferring, the microprocessor 4 selects the microprocessor 5. In the buffer 7, the microprocessor 5 has a disk volume 1
It is a data buffer for storing data to be read / written to 0.

Hereinafter, the effects of the present invention will be described with reference to FIGS. 2, 3 and 4.
Will be explained.

In FIG. 4, the disk volume 1 is on the upper device side.
An example of a series of commands for instructing a read operation to 0 is shown. The DEFINE EXTENT command 41 is a command for designating the allowable range of the seek operation and the write operation for the disk volume 10. The LOCATE RECORD command 42 is a command for designating the positioning information to be processed, the number of records, and the subsequent operation (read / write type, etc.). In this LOCATE RECORD command 42, a command for a positioning operation accompanied by a mechanical operation of seek and set sector is issued to the disk volume 10, so that the upper device is temporarily released by this command. After the positioning is completed, an interrupt request is issued to the upper device to reconnect and the READDATA command 43 is chained. The number of commands is LOCATE R
Only the number of commands designated by ECORD 42 is chained. Therefore, the magnetic disk control device 1 can know how many records of data to process before starting the data transfer with the host device.

The configuration information 30 of FIG. 3 is composed of data transfer rate information 31 of the higher-level device, data transfer rate information 32 of the disk volume 10 and command chain time (time interval between command issuance) information 33 of the higher-level device. . In the command chain time 33, the command and the command issuing interval are set by the microprogram of the microprocessor 4 by the DEFINE EXTENT command 41 and the LOCATE RECO command.
This is information recording the command chain time between the RD commands 42. The reconnection time 34 is a record of the time taken from the detection of the sector interrupt from the disk volume 10 by the microprocessor 5 to the issuance of a connection request to the host device and the permission of the connection request. N
It consists of historical information for each batch.

In the present invention, in order to explain the means for optimizing the amount of read-ahead data, the command chain time 33 and the reconnection time 34, which are the basic information for determining the amount of read-ahead data, are measured. It does not refer to the means itself.

These pieces of information can be measured by known techniques.

In FIG. 2, LOCATE RECORD
When D42 is received and it is detected that the data is read from the disk volume 10, the data transfer processing amount is calculated from the parameter (step 101). Next, the processing time on the host device side and the processing time on the disk volume 10 side are calculated (step 102). The processing time is predicted using the configuration information 30. By comparing the results, it is determined whether the ratio r of the processing time on the host device side and the processing time on the disk volume 10 side is X or more (X> 1) (step 103). If it is less than or equal to X, it is determined that there is not much difference in processing time, and the process proceeds to step 107. If it is greater than or equal to X, the process proceeds to step 104 to determine the amount of prefetch data. In step 104, the amount of data from the prefetching to the time when the higher-level device catches up is predicted. If the processing time ratio is r and the amount of data to be read ahead is S0, the amount of data processing S that can be processed before the higher-level device catches up can be expressed as the sum of geometric series as follows.

[0025]

## EQU00001 ## S = S0. (1-r * (i + 1)) / (1-r) where r * (i + 1) is the (i + 1) th power of r. i
Is the number of records processed before being caught up. (I
≤log (1 / S0) / maximum integer that satisfies logr)
That is, the i-th record is transferred to the higher-level device, and then used for the determination for prefetching processing separately from the higher-level device.

Step 105 is a step for calculating how many times the read-ahead is required for the data amount calculated in step 101. In step 106, the information to be read ahead by the microprocessor 5 is created. Then, in step 107, the seek and set sector instructions are issued, and the microprocessor 4 performs other services until there is an interrupt for ending positioning and prefetching. Normally, when the set sector is completed, an interrupt signal "sector ready" rises from the disk volume 10, and the microprocessor 5 is triggered by this to reconnect with the microprocessor 4 and the host device.

In step 108, the microprocessor 5
Starts prefetch processing after detecting sector ready. The microprocessor 5 issues a connection request to the microprocessor 4 when the amount of data calculated in step 104 is read ahead. The timing for making this connection request is determined in consideration of the reconnection time 34 so as not to exceed the capacity of the buffer 7 (step 109). Upon detecting the connection request from the microprocessor 5, the microprocessor 4 issues a reconnection request to the host device (step 110). When the reconnection request is received and the read command is issued from the host device, the microprocessor 4 transfers the prefetched data from the buffer 7 to the host device (step 111). In step 112, the processing statuses of the higher-level device and the disk volume 10 are monitored, and the data transfer method of the remaining transfer amount is carried out with the upper-level device being combined, or
Determine whether to disconnect the host device and execute prefetch again. When prefetching is performed again, a disconnection request is issued to the host device in step 113. If the upper device is connected, the end of data transfer is awaited in step 114. By performing the control as described above, it becomes possible to perform data transfer on the upper device side without depending on the data transfer capability of the lower device, and the upper device and the magnetic disk control device can be connected.

In this embodiment, the system has been described in which the microprocessor 5 independently performs prefetching and rejoins with the microprocessor 4 and the host device. However, prefetching may be started after the microprocessor 5 is joined. Further, if there is no response from the microprocessor 4 or the higher-level device within the specified time and the cache memory 8 is available, the prefetched data can be loaded into the cache memory, so the prefetched data is wasted. I won't.

[0029]

According to the present invention, when an input / output request is issued from a higher-level device, the amount of data to be read ahead between the external storage device and the external storage control device can be optimized, so that the transfer data is transferred to the control device. The time spent in the internal data buffer is minimized, and the throughput of the host device and the control device is improved.

[Brief description of drawings]

FIG. 1 is a block diagram showing an example of a computer system constructed using a magnetic disk subsystem that is an embodiment of the present invention.

FIG. 2 is a diagram showing a processing procedure of a micro program in the embodiment of the present invention.

FIG. 3 is a diagram showing control information used for control in the embodiment of the present invention.

FIG. 4 is a diagram showing an example of input / output instructions from a host device in the embodiment of the present invention.

[Explanation of symbols]

 1 ... Magnetic disk control device, 4, 5 ... Microprocessor, 10 ... Disk volume, 101, 114 ... Step showing an example of control operation, 30 ... History information, 41, 43 ... Channel command.

Claims (3)

[Claims] 1. A computer system comprising a plurality of external storage devices, an external storage control device having a data buffer for connecting and controlling these, and a host device, and between the external storage device and the host device. When performing data transfer, the data processing time of the host device side and the data processing time of the external storage device side are predicted, and the external storage device and the external storage device are externalized so that the transfer data stays in the data buffer for a minimum time. In an external storage control device equipped with means for prefetching data between storage control devices, the amount of data readahead on the external storage control device side and the time required to reconnect with the host device after detecting an interrupt after completion of positioning The amount of read-ahead data is determined by considering the difference between the data processing time on the device side and the data processing time on the external storage device side, and the data read-ahead from the external storage device to the external storage device is determined. A data transfer control method for an external storage control device, which is characterized in that 2. The external storage control device according to claim 1, wherein when data transfer is performed between the host device and the external storage device, the data is temporarily transferred to the host device according to the remaining data processing amount to be transferred to the host device. A means for disconnecting the connection of the external storage control device is provided, and data transfer between the external storage control device and the external storage device continues to prefetch data, and after buffering the required data amount, the host device A data transfer control method for an external storage control device, characterized in that when a connection request is issued to the external storage control device and the connection is permitted, data transfer between the external storage control device and the host device is restarted again. . 3. The external storage control device according to claim 1, wherein the connection between the external storage control device and the host device is delayed during data transfer between the external storage device and the external storage control device, If the data cannot be combined, the already buffered data is saved in the shared memory in the external storage control device, and if requested by the host device, the data in the shared memory is used for data transfer. A data transfer control method for an external storage control device, characterized by: