JP2854667B2 - Disk cache control method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial application field) The present invention relates to a disk cache control system for controlling reading or writing of data in a cache memory in a write-through disk cache system. About.

(Prior Art) For example, a computer having a magnetic disk device as a data memory is provided with a disk cache device. This disk cache device is a device in which a cache memory composed of RAM or the like is provided as an auxiliary storage area corresponding to each predetermined memory area of the magnetic disk device, that is, the disk cache device is stored in the magnetic disk device. By accessing some of the data with high access frequency in the cache memory, the speed of data access is increased.

Here, the disk cache control method includes a write-through method and a write-back method. In the former write-through method, when a data write request is issued from the host computer, the write request data is stored in the cache memory. If it exists (cache hit), data is written to the cache memory and the magnetic disk device. If the write request data does not exist in the cache memory (cache miss), it is written only to the magnetic disk device. Write data. In the latter write-back method, data is written only to the cache memory for the time being regardless of the cache hit or cache mishit, and the cache data is copied to the magnetic disk device by a later process.

In other words, in the above write-through method, the data write processing is always performed on the magnetic disk drive, and therefore, only when data is read when a cache hit occurs, the data access processing is performed in comparison with the data read from the magnetic disk drive. In the above-mentioned write-back method, the speed of reading data in the case of a cache hit and the speed of writing data to the cache memory can be increased as compared with the data access to the magnetic disk device. Can be In this case, when reading and writing data to and from the cache memory,
The storage order level of the data to be accessed in the cache memory is replaced with the highest level, so that frequently accessed data is always held at the upper level of the cache memory. .

Here, in the write-back type disk cache device, the data access time can be shortened in both the data reading and writing processes, but the data written in the cache memory is copied to the magnetic disk device. If a failure such as a power failure occurs before the failure occurs, there is a sufficient possibility that the contents will be lost. Therefore, a write-through type disk cache device is generally used.

(Problems to be Solved by the Invention) However, in the conventional disk cache device based on the above write-through method, both of the data read process and the write process at the time of a cache hit,
Since data level replacement in the cache memory is always performed, if data that receives only a write request is frequently accessed as an attribute of a certain data file, only the data to be written remains in the cache memory at an upper level. , And the data for reading which exerts the effect of the disk cache is gradually replaced with a lower level. That is, in the write-through type disk cache device, the effect of the disk cache is exhibited only when the cache hit data is read, so that the data write process with a low probability of receiving a read request later is performed. If the replacement control of the cache hit data to the highest level is performed until that time, the data with high read frequency in the cache memory is postponed to the lower level, and the effect of the disk cache is reduced.

On the other hand, even with the above-described conventional disk cache device, a sufficient cache effect can be obtained when performing file processing in which write data is immediately required as read data.

The present invention has been made in view of the above-described problems, and it is an object of the present invention to perform a file process in which write data is immediately requested as read data and a file process in which a high frequency of access to data that receives only a write request is performed. It is another object of the present invention to provide a disk cache control method capable of obtaining a maximum disk cache effect in processing.

[Effects of the Invention] (Means for Solving the Problems) That is, the disk cache control method according to the present invention controls the reading or writing of data in a cache memory in a write-through type disk cache device. , A magnetic disk device, a cache memory for storing a part of data stored in the magnetic disk device, data replacement means for replacing a storage order of a plurality of data stored in the cache memory, A cache data retrieval means for retrieving whether or not the requested data is present in the cache memory at the time of a read or write request of the cache memory; and transmitting the data requested at the time of the data read request to the cache memory.
When the data retrieving means finds that the data exists in the cache memory, the storage order of the read-requested data is replaced with the highest position, and the data is read. If it is found that the data does not exist in the cache memory, the read requested data is transferred from the magnetic disk device to the cache memory and read out with the storage order being the highest,
Along with this, if there is no free space in the cache memory, data reading means for expelling the data having the lowest storage order from the cache memory, and the data requested to be written at the time of the data write request is When the cache data search means finds that the data exists in the cache memory, the storage order of the write-requested data is replaced with the highest position, and the write-requested data is stored in the cache memory. If it is found that the data does not exist in the cache memory, the first data writing means writes the requested data to the magnetic disk device without storing the data in the cache memory; The cache data search means detects that the data requested to be written exists in the cache memory. In this case, the storage order of the write-requested data is held at the same position, and if it is found that the write-requested data does not exist in the cache memory, the write-requested data is not stored. Second data writing means for writing the written data to the magnetic disk drive without storing the data in the cache memory;
And a write mode selecting means for selecting the second data writing means according to the attribute of the data file.

(Operation) In other words, when performing file processing in which write data is immediately required as read data, the cache data storage order is controlled in accordance with the data access frequency based on the first data writing means. The read data can always be located at a higher storage level of the cache memory, and when performing file processing in which data that receives only a write request is accessed frequently, the second data writing means is used. By performing the replacement control of the cache data storage order according to the data read frequency based on the data, data that is not requested to be read can be preferentially positioned at the lower storage level of the cache memory. As a result, data having a high ratio of read requests is always preferentially left in the upper storage level of the cache memory, so that the use efficiency of the cache memory is improved and the maximum disk cache efficiency is obtained. It becomes possible.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a disk cache device 11 to which the disk cache control method is applied and its peripheral configuration. The disk cache device 11 includes a cache memory 12, a directory management table 13, and a directory control table 13. The unit 14, the LRU information management table 15, and the LRU control unit 16 are connected via bus lines 17, respectively.

On the other hand, the bus line of the disk cache device 11
A magnetic disk controller 18 is connected to the external device 17, and a channel device 19 on the host computer side and a magnetic disk device 20 are connected to the magnetic disk controller 18.

The disk directory management table 13 indicates which memory area of the magnetic disk device 20 stores data in the cache memory.
The tag information indicating where in the memory area 12 is stored and managed, and the directory control unit 14
Based on the tag information stored in the directory management table 13, it is determined whether or not the data to be read or written to the magnetic disk controller 18 exists in the cache memory 12, and a cache hit is determined. LRU signal or cache miss signal
(Least Recentry Used) Output to the control unit 16. The LRU control unit 16 controls the replacement of the storage level of the storage data in the cache memory 12 based on the LRU information stored in the LRU information management table 15.
Mode 1 and mode 2 are selected according to the attribute of the file to be processed. Here, when performing file processing in which write data to the cache memory 12 is immediately requested as read data, the mode 1 replacement control is selected, and file processing in which only a write request is accessed frequently is performed. Is performed, mode 2 replacement control is selected. The replacement mode selection means in the LRU control unit 16 may be set in advance by an OS (Operating System) or may be instructed and set by hardware.

That is, when a cache hit occurs due to a read request from the channel device 19, the cache hit data is replaced and updated to the highest level of the cache memory 12 in both the mode 1 and mode 2 replacement control. Even when a cache hit does not occur, data read from the magnetic disk device 20 is written to the highest level of the cache memory 12 (staging).
Further, when a cache hit occurs due to a write request from the channel device 19, in the mode 1 replacement control, the cache hit data is replaced and updated to the highest level of the cache memory 12, as in the case of the read request, and In the mode 2 replacement control, the cache hit data is updated in the cache memory 12 without changing the storage level. Then, when a write request is issued,
If there is no hit, writing is performed only on the magnetic disk device 20.

FIG. 2 is a flowchart showing a data write process accompanying a magnetic disk write request from the channel device 19. First, in step S1, when there is a magnetic disk write request from the channel device 19 to the magnetic disk controller 18, In step S2, the directory control unit
14 is the cache memory where the data corresponding to the write request is
12 to determine whether it exists in the cache memory 12.
If write request data exists in the cache,
The hit signal, and if not present, the cache miss signal is sent to the LRU in step S3.
Output to the control unit 16. In this step S3, the write request data exists in the cache memory 12, and the LR
When the cache hit signal is given to the U control unit 16, it is determined in step S4 whether the replacement control mode in the LRU control unit 16 is mode 1 or mode 2.

Here, when performing file processing in which write data to the cache memory 12 is immediately requested as read data, and the mode 1 is selected, in step S5, the LRU control unit 16 The cache hit data is replaced and updated to the highest level.

On the other hand, when performing file processing in which data receiving only a write request is frequently accessed and the mode 2 is selected, the LRU controller 16
Causes the cache hit data in the cache memory 12 to be written and updated without changing its storage level.

Then, in step S7, the magnetic disk controller 18 writes the data requested to be written from the channel device 19 to the magnetic disk device 20.

That is, when a cache hit occurs in response to a write request from the channel device 19, in the replacement control mode 1 for the cache memory 12, this cache hit data is replaced to the highest storage level. In 2, the cache hit data is updated at the same storage level without being replaced with the highest storage level.

On the other hand, if the write request data does not exist in the cache memory 12 and a cache mishit signal is given to the LRU control unit 16 in step S3,
No data is written to the cache memory 12 at all, and the process immediately proceeds to step S7, where the magnetic disk controller 18 writes the data requested to be written from the channel device 19 only to the magnetic disk device 20. .

FIGS. 3A and 3B show the data replacement operation in the cache memory 12 when the replacement control mode 1 is selected and when the replacement control mode 2 is selected, respectively. The cache memory 12 handles data in units of blocks, and [A] to [G] denote tag information indicating in which memory area the data in the corresponding block is stored in the magnetic disk device 20. I do.

For example, from the channel device 19 to the magnetic disk controller
When a data read request is issued to tag 18 and tag information [D] corresponding to the read request data exists in cache memory 12, directory control unit 14 sends LRU
When the cache hit signal is output to the control unit 16, the LRU control unit 16 sets the block corresponding to the tag information [D] to the highest level of the cache memory 12 in both the mode 1 and the mode 2. Replace and update. Then, the data stored in the cache memory block [D] is read out to the channel device 19 through the magnetic disk controller 18.

In this case, since data is read from the cache memory 12 and data is not read from the magnetic disk device 20, the data access time can be reduced.

Next, a description will be given with reference to the flowchart of FIG.
Has been requested (step S1), and the tag information [A] corresponding to the write request data exists in the cache memory 12 (step S2). On the other hand, when the cache hit signal is output (step S3), the LRU control unit 16 updates the block corresponding to the tab information [A] by replacing the storage level thereof with the highest level in mode 1 (step S3). In steps S5 and S6), in the case of mode 2, the storage level is updated without being replaced (step S6).

Then, the data stored in the cache memory block [A] is written to the memory area [A] of the magnetic disk device 20 through the magnetic disk controller 18 (step S7).

Here, the replacement control mode 1 is selected when performing file processing in which write data is immediately required as read data, and the block data [A] is selected.
In the case of the write process, since the replacement control of the write request data in the cache memory 12 to the highest level is performed as in the read process, the effect of the disk cache can be easily exerted at the time of the read request. Also,
The replacement control mode 2 is selected when performing file processing in which data that receives only a write request has a high access frequency. In the case of the write processing of the block data [A], the write control in the cache memory 12 is performed. Since the replacement control of the data to the highest level is not performed, the cache memory 12 can be used efficiently without delaying other data having a high read request ratio to the lower storage level.

Next, from the channel device 19, the magnetic disk controller
Since a data read request is issued to the memory 18 and the tag information [G] corresponding to the read request data does not exist in the cache memory 12, the directory control unit 14
When the cache mishit signal is output to the U control unit 16, the LRU control unit 16 transfers the block corresponding to the tag information [G] from the magnetic disk device 20 and causes the cache
The highest level of the memory 12 is written and updated (staging). The data stored in the cache memory block [G] is stored in the magnetic disk controller.
The data is read out to the channel device 19 through 18.

Here, in the setting state of the mode 1, when the previous block data [A] is written, the cache memory
The block [B] advanced to the 12 lowest levels is expelled. In this case, a block with a high access frequency that is likely to receive a read request is left in the upper level of the cache memory 12, and a block with a low access frequency is preferentially evicted.
The maximum disk cache effect can be obtained for file processing that handles a large amount of data that is read immediately after writing.

In the setting state of the mode 2, the block [A] updated at the lowest level when the previous block data [A] is written is expelled. In this case, blocks with high read frequency are preferentially left in the upper level of the cache memory 12, and blocks that receive only write requests are preferentially evicted. The maximum disk cache effect can be obtained for file processing in which the frequency of access to the received data is high.

FIG. 4 shows an example of an access pattern for the block (a) and the block (b) in the cache memory. In the disk cache device when the replacement control mode 1 is selected, read access is immediately performed even with write data. If received, the block (a) with a high access frequency at which the effect of the disk cache can be obtained is located at the upper level of the cache memory.

In addition, when the replacement control mode 2 is selected,
In the cache device, the block (a) that is frequently hit by the write request is not located at the upper level of the cache memory, so that the block (b) that receives the read request from time to time is not expelled. Even if the number of times of access is small, the effect of the disk cache can be surely exerted at the time of a read request for block (b).

Therefore, according to the disk cache control method as described above, for example, when performing file processing in which write data is immediately required as read data, by selecting the replacement control mode 1, both read and write access can be performed. Frequent data exists in the upper level of the cache memory, and the effect of high cache can be obtained. Also, when performing file processing in which data that receives only a write request is accessed frequently, selecting the replacement mode 2 enables
Since the replacement control of the write request data in the memory 12 to the highest level is not performed, data having a high ratio of read requests is not postponed to the lower storage level, and the cache
The memory 12 can be used efficiently, and a high cache effect can be obtained.

[Effects of the Invention] As described above, according to the present invention, the reading or writing of data in a cache memory in a write-through type disk cache device is controlled, and the magnetic disk device and the storage in the magnetic disk device are controlled. Memory for storing a part of the data stored in the cache memory, data replacement means for replacing the storage order of a plurality of data stored in the cache memory, and data requested at the time of a data read or write request. Cache data search means for searching whether or not the data exists in the cache memory; and when the data read request, the cache data search means searches for the presence of the data requested in the cache memory. If
When the storage order of the read-requested data is replaced with the highest position and read, and it is found that the read-requested data does not exist in the cache memory,
The read-requested data is transferred from the magnetic disk device to the cache memory and stored in the cache memory, and is read out with the highest storage order. If there is no free space in the cache memory, the storage order is highest. Data reading means for expelling lower-order data from the cache memory; and when the data requested to be written is found by the cache data search means to be present in the cache memory at the time of the data write request. Replaces the storage order of the write-requested data with the highest position, and if it is found that the write-requested data does not exist in the cache memory, replaces the write-requested data with the above-described data. First data writing means for writing to the magnetic disk device without storing the data in the cache memory; When the cache data search means finds that the requested data exists in the cache memory at the time of the data write request, the storage order of the write requested data is held at the same position. If it is found that the write-requested data does not exist in the cache memory, the write-requested data is not stored in the cache memory but is written to the magnetic disk device. 2 data writing means, the first data writing means, and the second data writing means.
And a write mode selecting means for selecting the data writing means in accordance with the attribute of the data file. Therefore, when performing file processing in which write data is immediately required as read data, and receiving only a write request In any file processing in the case of performing file processing in which data access frequency is high, data having a high read request ratio is always preferentially left in the upper part of the cache memory. The effect can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a disk cache device to which a disk cache control method according to one embodiment of the present invention is applied and its peripheral configuration. FIG.
FIGS. 3A and 3B are flow charts showing data write processing based on the cache control method, and FIGS. 3A and 3B show the data replacement operation in the cache memory based on the disk cache control method as compared with the case where the replacement control mode 1 is selected. FIG. 4 is a diagram showing an example of an access pattern for the block (a) and the block (b) in the cache memory in comparison with the case where the control mode 2 is selected. 11 ... Disk cache device, 12 ... Cache
Memory, 13 directory management table, 14 directory control unit, 15 LRU information management table, 16 R
LU control unit, 17 bus line, 18 magnetic disk controller, 19 channel device, 20 magnetic disk device.

Claims (1)

(57) [Claims] In a disk cache control method for controlling reading or writing of data in a cache memory in a write-through type disk cache device, a magnetic disk device and one of data stored in the magnetic disk device are provided. A data storage unit for replacing the storage order of a plurality of data stored in the cache memory; and the requested data is present in the cache memory at the time of a data read or write request. A cache data search means for searching whether or not to perform the data read request, when the data requested to be read is found in the cache memory by the cache data search means at the time of the data read request, The storage order of the data requested to be read is placed at the highest position. To read, said read requested data is above mentioned cache
If it is found that the data does not exist in the memory, the read-requested data is transferred from the magnetic disk device to the cache memory and stored, and is read out with the highest storage order. Data reading means for expelling the data having the lowest storage order from the cache memory when there is no free space in the cache memory, and the data requested to be written at the time of the data write request by the cache data search means. If it is found that the data exists in the cache memory, the storage order of the data requested to be written is replaced with the highest position,
When it is found that the data requested to be written does not exist in the cache memory, the first data to be written to the magnetic disk device without storing the data requested to be written in the cache memory is stored. Data writing means, when the data requested to be written is found to be present in the cache memory by the cache data searching means at the time of the data writing request, the storage order of the data requested to be written is changed. Hold in the same position,
If it is found that the write-requested data does not exist in the cache memory, a second step of writing the write-requested data to the magnetic disk device without storing the data in the cache memory is performed. A disk cache control system comprising: a data write unit; and a write mode selection unit that selects the first data write unit and the second data write unit according to an attribute of a data file. .