JPH096676A - Control method for magnetic disk cache - Google Patents

Abstract

PURPOSE: To shorten the processing time needed for the irregular writing operations in a cache control method which applies the store-in-write processing (fast write processing). CONSTITUTION: If the data at the position where the data should be written by a host device are not stored in a cache memory (S11), an instruction is produced to move the head of a magnetic disk to a target position (S12). The target position is searched while the data are read out of a magnetic disk medium (S13), and the track position of the data stored in the cache memory is registered on a cache memory control table (S14). The write data are stored in the cache memory (S15). Then the processing is started to write the write data stored in the cache memory into a magnetic disk device right before a series of instruction string processing are finished (S16), and the end of the write processing instruction string is reported to the host device (S17).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling a magnetic disk cache, and more particularly to a method for controlling a magnetic disk cache having a cache memory and performing high speed write processing.

[0002]

2. Description of the Related Art In recent years, as the CPU speed of computers has increased, the input / output speed to / from an external storage device often adversely affects the computer processing, and it is particularly desirable to increase the input / output processing speed of the external storage device. ing. Therefore, in the field of a magnetic disk device which is a typical external storage device, a method of mounting a cache memory is generally known as a method of increasing the speed of input / output.

According to this method, when data is read from the magnetic disk device, the read data is transferred to the host device and at the same time stored in the cache memory in the disk control unit so that the same part is read again from the host device. When instructed, the data stored in the cache memory is transferred to the host device without actually reading the data from the magnetic disk device.

Further, when writing data to the magnetic disk device, the data sent from the host device is not written to the magnetic disk device but is written to the cache memory composed of semiconductor memory elements, and the write command is terminated to the host device. Make a report. Then, the write data in the cache memory is written from the cache memory to the magnetic disk device after a lapse of a certain time or when a certain amount of write data is stored in the cache memory. Write processing using such a cache is called store-in-write processing or high-speed write processing.

Generally, when the data at the position to be accessed is present in the cache memory, this state is called a cache hit, and conversely, when the data at the position to be accessed is not present in the cache memory, this state is called. I'm missing a cache miss. In the write / read operation to / from the magnetic disk medium, the head of the magnetic disk device is moved to determine the access position. Therefore, the seek operation of moving the magnetic head to a target track on the magnetic disk medium and the magnetic disk medium Data writing / reading is performed after a search operation for searching for an actual access position.

In the case of a cache hit, these operations can be executed only by accessing the memory and are completed in a short time. In the case of a cache miss, however, the physical operation of the magnetic disk device is involved, and therefore, compared to the access to the cache memory. It takes much longer. As described above, the cache memory utilizes the high-speed operation of the semiconductor memory element, so that the input / output processing speed of the magnetic disk device can be apparently increased from the host device.

[0007]

In the above-described conventional high-speed writing process, the effect of high-speed writing cannot be sufficiently obtained when the position on the magnetic disk medium accessed by the host device is irregular and sparse. However, the response performance may be adversely deteriorated due to the increase in the operation occupation time of the magnetic disk device.

Further, the probability of the data at the target position existing in the cache memory is reduced, resulting in a cache miss. After actually reading the data on the magnetic disk medium, the host device is searched for the target write position. If the host device accesses another position on the same magnetic disk medium after the write data from the host is stored in the cache memory and the host device is notified of the completion of the write processing at this point, the cache memory The magnetic head is moved to a new access position because it is unlikely that the data exists above.

Therefore, when the data left in the cache memory is first read out after this and an attempt is made to write it in the magnetic disk medium, the magnetic head has already moved to another position, and the magnetic field is returned to the original position again. The head must be returned before writing. Therefore, even if the magnetic disk device is occupied for a long time, and subsequently the host device issues a read command for a portion that does not exist in the cache memory, and the magnetic disk device needs to actually access it, It is necessary to wait until the write processing is completed and the magnetic disk device is released.

Therefore, even if the write-in command from the host device can be processed at high speed by the store-in-write process, the command from the upper-level device is kept waiting for the subsequent write-in process to the magnetic disk device. Has the drawback that it does not have the effect of improving performance.

[0011]

SUMMARY OF THE INVENTION The present invention is a method of controlling a magnetic disk cache having a cache memory and performing high-speed write processing, wherein data at a position where data is to be written in the write processing from a higher-level device is the cache. If it does not exist in the memory, the write data is stored in the cache memory, and the process of writing the write data in the cache memory to the magnetic disk device is started immediately before the end of the series of instruction sequence processing, and then the upper device is It is characterized in that the end of the write processing instruction sequence is reported.

Further, the data at the target position for writing the data exists in the cache memory, the write data is stored in the cache memory in the write processing from the host device, and the write processing is performed immediately before the end of the series of instruction sequence processing. After comparing the performed track position with the contents of the register for storing the track position of the magnetic head of the magnetic disk device, and when both match, after starting the process of writing the write data in the cache memory to the magnetic disk device The end report of the write processing instruction sequence is sent to the host device.

[0013]

Next, the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing a magnetic disk controller to which an embodiment of the present invention is applied. As shown in FIG. 1, the magnetic disk controller 1 is connected to a host device 2 and a magnetic disk device 3, respectively. The host device 2 is a host device that gives an instruction to the magnetic disk control device of the present invention, and the magnetic disk device 3 sends data to a magnetic disk medium (not shown) via a magnetic head (not shown). Write and read.

The magnetic disk control device 1 includes a microprocessor 11, a host device connection unit 12 connected to the host device 2, a drive connection unit 13 connected to the magnetic disk device 3, and read data from the magnetic disk device 3. And a cache memory 14 for storing the write data to the magnetic disk device 3, a cache memory management table 15 for managing the data stored in the cache memory 14, and a head position register for storing the position of the magnetic head of the magnetic disk device 3. 16 and.

The microprocessor 11 of the magnetic disk controller 1 controls the overall operation of the magnetic disk controller 1 according to a control program. The host device connection unit 12 is
When data transfer, command transfer and status transfer with the higher-level device 2 are performed, the input / output processing is controlled. The drive connection unit 13 controls the input / output processing of data transfer, command transfer, and status transfer to the magnetic disk device 3. The cache memory 14 stores the data read from the magnetic disk device 3 and also temporarily stores the write data sent from the host device 2.

The cache memory management table 15 is a management table for associating a data storage address on the cache memory 14 with a recording position on the magnetic disk device 3, and data in an area of the cache memory 14 is read data. Whether or not it is write data, and if it is read data, from which position of the magnetic disk device 3 the data was read, and if it is write data,
The position in the magnetic disk device 3 where the data should be written is stored. The storage area in the cache memory 14 is finely divided so that a plurality of read data and write data can be stored and managed.

The head position register 16 is a register for storing the track number where the magnetic head is currently located in the magnetic disk device 3, and its contents are updated by the microprocessor 11. When the microprocessor 11 executes a seek command which is a magnetic head positioning command for the magnetic disk device 3, the microprocessor 11 stores the track number of the seek in the head position register 16.

The above is the configuration of the magnetic disk controller for realizing the magnetic disk cache control method of the present invention.

Next, the operation of the embodiment of the present invention will be described.

FIG. 2 is a flow chart showing the operation of the first embodiment of the present invention. The present embodiment is applied to the magnetic disk control device 1 shown in FIG. 1 that does not include the head position register 16.

Referring to FIGS. 1 and 2, instructions and data sent from the host device 2 are transferred to the microprocessor 1 via the host device connecting portion 12 of the magnetic disk controller 1.
1 is input and analyzed. The microprocessor 11
If the command controls the magnetic disk device 3 according to the analyzed command and the command is to operate the magnetic disk device 3, the operation command is sent to the magnetic disk device 3 via the drive connection unit 13.

In the present embodiment, the read operation is the same as that of the conventional magnetic disk controller, and when the data read from the magnetic disk device 3 is stored in the cache memory 14, the magnetic When the read command for the portion is sent from the host device 2, the disk controller 1 transfers the data stored in the cache memory 14 to the host device 2 without accessing the magnetic disk device 3. Usually, the write command from the higher-level device 2 is accompanied by a seek command and a search command that specify the write position.

First, when the seek instruction or the search instruction is accepted, the microprocessor 11 searches the cache memory management table 15 to determine whether the data of the area including the write position is stored in the cache memory 14, that is, , It is determined whether there is a cache hit or a cache miss (S11).

If the data at the seek or search position is not in the cache memory 14, a cache miss will occur, so that the microprocessor 11 instructs the magnetic disk device 3 to move the head of the magnetic disk to the target position. The data is sent (S12), and the target position is searched while reading the data on the magnetic disk medium (S1).
3). At this time, the data read from the magnetic disk medium is also stored in the cache memory 14 at the same time, and its track position is registered in the cache memory management table 15 (S14). Then, the write data is received from the host device 2 and stored in the cache memory 14 (S15).

Here, in this embodiment, the microprocessor 11 starts reading the data stored in the cache memory 14 from the magnetic disk device 3 (S).
16) Furthermore, the completion of the write command is reported to the higher-level device 2 without waiting for the completion of writing the data (S1).
7). Then, the microprocessor 11 monitors completion of writing of the write data to the magnetic disk medium during standby (S18).

When an instruction to access the magnetic disk device 3 is issued during this period, it is necessary to wait until the writing operation is completed, but in the present embodiment, after the writing position is searched, the magnetic head is changed to another one. Since the write operation to the magnetic disk medium is started before moving to the track position, it is not necessary to realign the track position of the magnetic head, and the operation occupation time of the magnetic disk device accompanying the write to the magnetic disk medium is shortened. It

Further, in the determination step of S11, if the data at the write position exists in the cache memory 14, that is, if there is a cache hit, the cache memory 14 will have the same contents as in the conventional store-in-write process. The search operation is performed using the data of (S1
9). At this time, the actual magnetic disk device 3 is not accessed. Then, the write data is received from the host device 2 and stored in the cache memory 14 (S20).

When the writing of the data to the cache memory 14 is completed, the microprocessor 11 reports the completion of the write instruction to the host device 2 (S2).
1). At this time, the write data stored in the cache memory 14 is written in the magnetic disk device 3 after a fixed time or when a fixed write data is stored in the cache memory.

In this embodiment, since the writing to the magnetic disk medium is started immediately before the completion report of the write command to the upper apparatus 2, the operation occupation time of the magnetic disk apparatus 3 is The command occupancy time, which is the time until the command is transmitted, cancels each other out, and the operation occupied time of the magnetic disk device 3 seems to be shorter by the command interval as seen from the host device. As a result, the waiting time for the next access due to the occupation of the magnetic disk device 3 can be shortened.

Next, the operation of the second embodiment of the present invention will be described with reference to FIGS.

The present embodiment is applied to the magnetic disk controller 1 shown in FIG. 1 provided with the head position register 16 and stores the track position of the magnetic head on the magnetic disk medium in the case of a cache hit. Using the head position register 16 that operates, a higher effect can be obtained.

Here, in the flowchart shown in FIG. 3, S20 is inserted between S20 and S21 of the flowchart shown in FIG.
The judgment step of 20 'is inserted. Therefore,
In the present embodiment, the description of the duplicated contents will be omitted.

Referring to FIG. 3, first, the operation when a cache miss occurs in S11, that is, when the data of the target position is not stored in the cache memory 14, is explained in the first embodiment described above. The operation is similar, but the microprocessor 11 updates the contents of the head position register 16 every time the position of the magnetic head of the magnetic disk device 3 is changed. Therefore, the microprocessor 11 can know the current position of the magnetic head by reading the contents of the head position register 16.

On the other hand, in S11, if there is a cache hit, that is, if the data at the target position exists in the cache memory 14, the microprocessor 11
Before the end of the series of instructions for the write process, the track address at which the data written in the cache memory 14 by the write command from the contents of the cache memory management table 15 should be written on the magnetic disk medium, the head position register 16, and Compare the contents of. That is,
It is determined whether or not the position of the magnetic head is in a position where data can be read out from the cache memory (S20 ').

If the two match, the process of writing the data in the cache memory 14 to the magnetic disk medium is started (S16). If they do not match, the end of the writing process is reported to the higher-level device 2 (S2).
1). This control method is to judge the start of writing to the magnetic disk medium when the position of the magnetic head is already at the position where the write data in the cache memory 14 is immediately written to the magnetic disk medium. This allows
The useless operation of the magnetic head can be further reduced, and the operation occupation time of the magnetic disk device 3 can be reduced.

[0037]

As described above, according to the present invention, in the irregular write processing to the magnetic disk medium, the write data is stored in the cache memory, and the data is written to the magnetic disk medium immediately before the completion of a series of write commands. Since writing is started, the magnetic head can start writing at the current track position, and the operation occupation time of the magnetic disk device accompanying the movement of the magnetic head can be shortened.

Further, since the completion of the write command is reported to the host device at the same time when the writing from the cache memory to the magnetic disk medium is started, the write processing time to the magnetic disk device can be offset with the command interval from the host device. it can.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a magnetic disk control device to which an embodiment of the present invention is applied.

FIG. 2 is a flowchart showing an embodiment of the present invention.

FIG. 3 is a flowchart showing another embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 magnetic disk control device 2 host device 3 magnetic disk device 11 microprocessor 12 host device connection part 13 drive connection part 14 cache memory 15 cache memory management table 16 head position register S12 to S21 processing step S11, S20 'determination step

Claims (2)

[Claims] 1. A method for controlling a magnetic disk cache having a cache memory and performing high-speed write processing, comprising:
When the data at the position where the data is to be written does not exist in the cache memory in the write processing from the host device, the write data is stored in the cache memory, and the write in the cache memory is performed immediately before the end of the series of instruction sequence processing. A method for controlling a magnetic disk cache, characterized in that after starting a process of writing data to a magnetic disk device, a completion report of a write processing instruction sequence is sent to the upper device. 2. The data at the target position for writing the data exists in the cache memory, the write data is stored in the cache memory in the write processing from the host device, and the write processing is performed immediately before the end of the series of instruction sequence processing. Compare the performed track position with the contents of the register that stores the track position of the magnetic head of the magnetic disk device,
If the two match, a method for controlling the magnetic disk cache is characterized in that, after starting the process of writing the write data in the cache memory into the magnetic disk device, the end of the write processing instruction sequence is reported to the upper device. .