JP2001014219A - Method and device for controlling cache - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a useless writing operation to a magnetic disk in a recording and reproducing device such as a magnetic disk drive provided with a cache memory. SOLUTION: A cache memory controlling part 4 judges whether the data of an address exist in a cache memory 5 bout each of a plurality of addresses to which a write request is sent from a host computer 1. A data comparing part 6 compares write data from the computer 1 with data stored in the memory 5 for each of addresses whose data are decided as stored in the memory 5. A disk array controlling part 7 writes the data sent from the computer 1 to a magnetic disk for only an address judged as uncoincidental in comparison by the part 6 among the address whose data are judged as stored in the memory by the part 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a recording / reproducing device using a magnetic disk as a storage medium, such as a magnetic disk device and a magnetic disk array device, and more particularly, to a cache in a recording / reproducing device having a cache memory. Related to control technology.

[0002]

2. Description of the Related Art A magnetic disk device or the like using a magnetic disk as a storage medium can store large-capacity data at low cost, but has a problem that access speed is slow because it has a mechanically movable portion. In order to improve such a problem, a cache memory including a semiconductor memory has been conventionally used.

A conventional recording / reproducing apparatus equipped with a cache memory checks whether data requested to be read exists in the cache memory when a data read request is received from a host device such as a host computer. If so, the data is transferred from the cache memory to the host device, and if not, the data is transferred from the magnetic disk device to the host device. Also, when there is a data write request from the host device, it is checked whether or not the data at the address of the write request exists in the cache memory, and if there is, the data is written to the cache memory and the data does not exist. In such a case, data is written to the magnetic disk. Such a technique is described in, for example, JP-A-9-91198. In the technology described in this publication, in order to match the data stored in the cache memory with the data on the magnetic disk, the cache memory is read out of the cache memory at a time when access from the host device is interrupted. It is determined whether the written data matches the data on the magnetic disk corresponding to the data, and if not, the data is written to the magnetic disk. However, the technique described in the above publication makes it possible to determine whether or not the data on the cache memory and the data on the magnetic disk match based on control information indicating whether or not the data has been written on the magnetic disk. Therefore, the judgment is not actually made by comparing the two.

[0004]

Generally, in a higher-level device such as a host computer, when data is transferred to and from a recording / reproducing device, data transfer is performed in units of data for a plurality of continuous addresses. To do. Therefore, at the time of a data write request, data of a plurality of addresses sent from the higher-level device to the recording / reproducing device may include data of an address that has not been updated since the previous write request. If such data is written to the cache memory, the control information about the data indicates that the writing to the magnetic disk has not been completed in the above-described conventional technique. Although the data corresponding to the data written on the magnetic disk is the same, the write processing on the magnetic disk is performed again. Thus, in the conventional technology,
There is a problem that useless write processing may be performed on the magnetic disk.

Accordingly, an object of the present invention is to prevent a useless write process from being performed on a magnetic disk.

[0006]

In order to achieve the above object, a cache control device according to the present invention uses a magnetic disk as a storage medium and stores a copy of a part of data stored on the magnetic disk. A cache control device in a recording / reproducing device having a cache memory, wherein when data of an address requested to be written by a host device is stored in the cache memory, the write data sent from the host device and the Comparing with the data of the address stored in the cache memory,
The writing data is written to the magnetic disk only when the comparison does not match.

Further, the cache control device of the present invention uses a magnetic disk as a storage medium and stores data stored on the magnetic disk in order to cope with a case where a write request is made to a plurality of addresses. A cache control device in a recording / reproducing device having a cache memory in which a part of a copy is stored, wherein when a write request for a plurality of addresses is issued from a host device, the cache memory of the plurality of addresses is Is compared with the write data of the address sent from the higher-level device and the data of the address stored in the cache memory. Has a configuration for writing the write data.

More specifically, a cache control device according to the present invention uses a magnetic disk as a storage medium and has a cache memory in which a copy of a part of data stored on the magnetic disk is stored. A cache memory control unit for determining, for each of a plurality of addresses for which a write request has been made from a higher-level device, whether or not data of the addresses is stored in the cache memory; For each address determined by the memory control unit to store the data of the cache memory, the write data for the address sent from the higher-level device and the data of the address stored in the cache memory are transmitted from the higher-level device. A data comparing unit to be compared, and Only the addresses, out of the addresses, for which the cache memory control unit determined that the data was not stored in the cache memory and the addresses for which the data comparison unit determined that the comparison did not match were sent from the higher-level device. A controller for writing write data to the magnetic disk.

In this configuration, the cache memory control unit determines, for each of a plurality of addresses for which a write request has been made from a higher-level device, whether or not the data at the address is stored in the cache memory, and performs a data comparison. For each of the addresses determined by the cache memory control unit to store the data of the cache memory, the write data for the address sent from the higher-level device and the data of the address stored in the cache memory The control unit compares only the addresses of the write-requested addresses for which the cache memory control unit determines that the data is not stored in the cache memory and the addresses for which the data comparison unit determines that the comparison does not match. , Write data sent from the host device Written care disk.

[0010]

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention. A host computer 1 and a magnetic disk array device 2 are shown.
Are connected by an interface such as a SCSI interface. The host computer 1 and the magnetic disk array device 2 can perform data transfer in units of data for a plurality of addresses.

The magnetic disk array device 2 includes a host interface control unit 3, a cache memory control unit 4,
A cache memory 5, a data comparison unit 6, a disk array control unit 7, and a plurality of magnetic disk devices 8-1 to 8-
n.

The host interface control section 3 controls the exchange of data between the host computer 1 and the magnetic disk array device 2, and can be realized by an interface control LSI or the like.

The cache memory 5 stores a copy of a part of the data stored in the magnetic disk devices 8-1 to 8-n, and is a semiconductor capable of accessing data at a higher speed than a magnetic disk. Implemented by memory. The cache memory 5 includes a plurality of cache pages, and each cache page stores data for one address.

The cache memory control unit 4 has the following functions and the like.

A. A function of managing which address data is stored in each cache page of the cache memory 5. b. A function of determining whether or not data at an address for which writing or reading has been requested exists in the cache memory 5. c. If the data of the address requested to be read exists in the cache memory 5, the data is transferred from the cache memory 5 to the host computer 1, and if not, the data is transferred to the magnetic disk drive 8-i (1 ≦ i ≦ n). Function to transfer the data of the host computer 1 to the host computer 1. d. If the data at the address requested to be written exists in the cache memory 5, the write data from the host computer 1 matches the data at the address stored in the cache memory 5 using the data comparison unit 6. A function to check whether or not the data match, and to write data to the magnetic disk drive 8-i only when the data does not match. This function is a function unique to the present invention. e. A function of writing write data from the host computer 1 to both the cache memory 5 and the magnetic disk device 8-i when the data at the address requested to be written does not exist in the cache memory 5;

The data comparison unit 6 is a host computer 1
Has a function of comparing write data transmitted from the cache memory 5 with data corresponding to the write data stored in the cache memory 5.

The disk array control unit 7 has a function of reading and writing data from and to arbitrary addresses of the magnetic disk devices 8-1 to 8-n, and can be realized by a control LSI.

Next, the operation of this embodiment will be described.

First, the operation when the host computer 1 reads data from the magnetic disk array device 2 will be described.

When reading data from the magnetic disk array device 2, the host computer 1 issues a read request to the magnetic disk array device 2. The read request includes, as address information, an address (head address) at which the head data is stored in the data to be read, and a read data size indicating how many addresses of data are to be read from the head address. include. For example, when reading the data stored in the addresses A10, A11, and A12, the host computer 1 uses the start address “A1” as the address information.
0 "and a read request including the read address size" 3 "will be issued.

A read request from the host computer 1 is accepted by the host interface control unit 3 in the magnetic disk array device 2.

When the host interface control unit 3 receives a read request, the cache memory control unit 4 pays attention to the smallest address among the read destination addresses indicated by the address information contained therein, and the data of that address is It is determined whether or not it exists in the cache memory 5 (A1, A2 in FIG. 2).

If it is determined that the data exists in the cache memory 5 (A2: YES), the corresponding data is read from the cache memory 5 and passed to the host interface control unit 3 (A3, A4). On the other hand, if it is determined that the cache page does not exist in the cache memory 5 (A2 is NO), one empty cache page is reserved in the cache memory 5 (A5), and the disk array control unit 7 is used. The data at the address of interest is read from the magnetic disk drive 8-i (A6), written to the free cache page secured in A5, and passed to the host interface controller 3 (A7). A
5 to secure a free cache page, if a free cache page exists, one of the free cache pages is reserved. If no free cache page exists, L
Select one cache page by RU method, etc.
The selected cache page is reserved as a free cache page.

When the processing of A4 or A7 is completed, the cache memory control unit 4 determines whether an unprocessed address exists in the read destination address (A).
8). When it is determined that an unprocessed address exists (A8: YES), the process of A1 is performed again. On the other hand, when it is determined that there is no unprocessed address (A8: NO), the host interface controller 3 is notified of the end of the process (A9).

When the read data is notified from the cache memory control unit 4, the host interface control unit 3 holds the read data internally, and when the read data of a predetermined address is stored, transfers the read data to the host computer 1 collectively. I do. However, when the end of the processing is notified from the cache memory control unit 4, the currently held read data is collectively transferred to the host computer 1.

Next, the operation when the host computer 1 writes data to the magnetic disk array device 2 will be described.

When writing data to the magnetic disk array device 2, the host computer 1 issues a write request to the magnetic disk array device 2 including write data and address information indicating the write position. The write data can have any size as long as it is smaller than a predetermined size. However, it is necessary to use continuous address data. The address information includes an address (head address) indicating the write position of the head write data, and a write data size indicating how many addresses of data are to be written. For example, addresses A20, A21, A22, A
When writing data to the host computer 23, the host computer 1 issues a write request including write data for four addresses, and also including a head address “A20” and write data size “4” as address information.

The write request issued from the host computer 1 is accepted by the host interface control unit 3 in the disk array device 2.

When the host interface controller 3 receives a write request, the cache memory controller 4 secures an empty cache page in the cache memory 5 (FIG. 3, B1). At that time, the cache memory control unit 4
Secures empty cache pages of the number of pages corresponding to the size of the write data, such as securing four empty cache pages if the write data is for four addresses.

Thereafter, the cache memory control unit 4 pays attention to the smallest one of the write destination addresses indicated by the address information in the write request (B
2) It is determined whether the data at the address exists in the cache memory 5 (B3).

Then, when it is determined that the file does not exist (B3
Is NO), first, write the write data to the currently focused address included in the write request into one of the free cache pages secured in B1 (B
8) Next, a pair of the number of the cache page in which the data is written in B8 and the address of interest at present is additionally registered in a list (not shown) (B9). The data of the cache page whose number is registered in this list is
This is the data to be written to the magnetic disk device.

On the other hand, when it is determined that the data of the address currently being watched exists in the cache memory 5 (YES in B3), first, a holding instruction is output to the data comparing section 6, and The write data for the currently focused address is written to one of the free cache pages secured in B1 (B4). Note that the write data is also supplied to the data comparison unit 6. When the write data is added from the cache memory control unit 4 after the holding instruction is added, the data comparing unit 6 holds the write data internally.

After that, the cache memory control unit 4 outputs a comparison instruction to the data comparison unit 6 and sets two cache pages of the cache memory 5 (the cache page which caused the determination result of B3 to be YES). ,
S3 of the data of the currently focused address stored in the cache page in which the data is written in B4)
The content of the cache page that has caused the determination result to be YES is read (B5). The data read from the cache memory 5 is added to the data comparison unit 6, and the data comparison unit 6 receives the data read from the cache memory 5 after receiving the comparison instruction from the cache memory control unit 4. , And the data stored therein, and compares the comparison result with the cache memory control unit 4.
Notify. That is, the data comparison unit 6 compares the data of the currently focused address sent from the host computer 1 with the data of the currently focused address originally stored in the cache memory 5, and compares the comparison result. The cache memory control unit 4 is notified.

The cache memory control unit 4, when notified of the comparison match from the data comparison unit 6 (B6: YES)
Of the two cache pages storing the data of the address of interest at present,
Release the cache page that caused S (B
10). On the other hand, when the comparison mismatch is notified (B6: NO), a pair of the number of the cache page in which the data is written in B4 and the address currently focused on is additionally registered in a list (not shown). Thereafter (B7), the process of B10 is performed.

The cache memory control unit 4 performs the above B2
To B10 are repeated until there are no unprocessed addresses (until B11 becomes NO).

When there are no unprocessed addresses,
The cache memory control unit 4 focuses on one of the pairs of the cache page number and the address registered in the list, reads data from the cache page of the cache page number, further reads the read data and the address. To the disk array control unit 7. The cache memory control unit 4 performs this processing for all pairs registered in the list (B12).

When the data and address are sent from the cache memory control unit 4, the disk array control unit 7
The data is written to a portion corresponding to the address of the magnetic disk devices 8-1 to 8-n.

Next, the operation at the time of a data write request will be described with a specific example.

Now, for example, as shown in FIG. 4, three magnetic disk drives 8-
1 to 8-3, and the magnetic disk devices 8-1 to 8-3
Data of the addresses A1, A2, A3, A4 of the cache memory 5 are cache page numbers P7, P8, P9,
It is assumed that the data has already been read into the cache page of P10.

In this state, it is assumed that a write request including write data for addresses A1, A2, and A3 and address information (head address "A1", write data size "3") is sent from the host computer 1. Note that, of the write data for the addresses A1, A2, and A3, only the write data for the address A2 has been updated since the previous write request, and the write data for the other addresses A1 and A3 have been updated since the previous write request. Suppose not.

When the host interface controller 3 receives the write request, the cache memory controller 4 secures three free cache pages in the cache memory 5 (B1). In this example, it is assumed that the cache pages of the cache page numbers P3, P4, and P5 have been secured as free cache pages.

Thereafter, the cache memory control unit 4 pays attention to the address A1, and determines whether or not the data at that address exists in the cache memory 5 (B2, B
3). In the case of this example, since the data of the address A1 is written in the cache page of the cache page number P7 of the cache memory 5, the cache memory control unit 4 outputs a holding instruction to the data comparison unit 6, and As shown in FIG. 5, the write data for the address A1 sent from the host computer 1 is written to the empty cache page P3 secured in B1 (B
4).

Thereafter, the cache memory control unit 4 causes the data comparison unit 6 to compare the data of the address A1 sent from the host computer 1 with the data of the address A1 stored in the cache page P7 (B
5). In the case of this example, since the data at the address A1 has not been updated since the last write request, the comparison result is the same (YES at B6).

As a result, the cache memory control unit 4
After releasing (unused) the cache page P7, pay attention to the address A2 (B10 and B11 are YES, B
1). Since the data at the address A2 also exists in the cache page P8 of the cache memory 5, the determination result at B3 becomes YES, and the processing at B4 and B5 is performed. But,
Since the data at the address A2 has been updated since the previous write request, the determination result at B6 is NO. B6
Is NO, the cache memory control unit 4 sets the cache page number P in which the data was written in step B4.
A pair of the address 4 and the current address of interest A2 is additionally registered in the list (B7), and then the cache page P8 is released (B10).

When the process of B10 is completed, the cache memory control unit 4 pays attention to the address A3 (B2). Since the data at the address A3 exists in the cache memory 5 and has not been updated since the previous write request, the same processing as when the address A1 is noted is performed.

When the processing for the address A3 is completed,
The cache memory control unit 4 performs the process of B12. In the case of this example, since only the pair of the cache page number P4 and the address A2 is registered in the list, the cache memory control unit 4 stores the data stored in the cache page of the cache page number P4 in the cache memory. 5 and sends it to the disk array controller 7 and sends the address A2 paired with the cache page number P4 to the disk array controller 7 (B12).
Thereby, as shown in FIG. 5, the disk array controller 7 writes the data sent from the cache memory controller 4 to the address A2 of the magnetic disk device 8-3.

As described above, according to the present embodiment, of the data at the addresses A1, A2, and A3 included in the write request, only the data at the address A2 that has been updated since the previous write request is stored on the magnetic disk. Since it becomes possible to write to the device 8-3, it is possible to prevent useless write processing such as rewriting the data of the addresses A1 and A3 that have not been updated since the previous write request to the magnetic disk device. it can. Address A
1, a magnetic disk drive to which A3 is assigned
Since no write operation is performed on the data at the addresses A1 and A3, the memory devices 2 and 8-1 can respond to reading and writing of other data.

FIG. 6 is a block diagram of another embodiment of the present invention, in which the host computer 1 and the magnetic disk drive 12 are connected via an interface such as a SCSI interface.

The difference between the magnetic disk device 12 of this embodiment and the magnetic disk array device 2 of FIG. 1 is that a magnetic disk 18 is provided instead of the magnetic disk devices 8-1 to 8-n. The difference is that a magnetic medium controller 17 for inputting and outputting data to and from the magnetic disk 18 is provided instead of the array controller 7.

The operation of this embodiment is almost the same as that of the embodiment shown in FIG. 1, except for the following points. In the embodiment shown in FIG. 1, when the cache memory control unit 4 reads data at A6 in FIG. 2, the data is read using the disk array control unit 7, but in the present embodiment, the magnetic medium control unit The data is read from the magnetic disk 18 by utilizing the data 17. In the embodiment shown in FIG. 1, the cache memory controller 4 sends data and addresses to the disk array controller 7 at B12 in FIG.
In this embodiment, data and address are sent to the magnetic medium control unit 17 to write data to the magnetic disk 18 in this embodiment.

[0052]

As described above, according to the present invention, when the data at the address requested to be written by the host device is stored in the cache memory, the write data sent from the host device and the data are stored in the cache memory. Is actually compared with the data at the above address, and the data is written to the magnetic disk only when the comparison result does not match. Therefore, the same data as the data written to the magnetic disk is written to the magnetic disk again, which is a wasteful write. Processing can be prevented. As a result, data write performance can be improved.

When the present invention is applied to a magnetic disk array device, data that has not been updated since the previous write request among the data at the write-requested address is written to the magnetic disk device. Therefore, other data can be read from and written to the magnetic disk device. Therefore, data read / write performance of the entire system can be improved.

[Brief description of the drawings]

FIG. 1 is a block diagram of one embodiment of the present invention.

FIG. 2 is a flowchart showing a processing example of a cache memory control unit 4 at the time of a data read request.

FIG. 3 is a flowchart showing a processing example of a cache memory control unit 4 at the time of a data write request;

FIG. 4 is a diagram for explaining an operation at the time of writing data.

FIG. 5 is a diagram for explaining an operation at the time of writing data.

FIG. 6 is a block diagram of another embodiment of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 host computer 2 magnetic disk array device 3 host interface control unit 4 cache memory control unit 5 cache memory 6 data comparison unit 7 disk array control unit 8-1 to 8 -n magnetic disk device 12 Magnetic disk device 17 ... Magnetic medium controller 18 ... Magnetic disk

Claims (6)

[Claims] 1. A cache control method in a recording / reproducing apparatus having a magnetic disk as a storage medium and having a cache memory in which a copy of a part of data stored on the magnetic disk is stored. If the data at the address requested to be written from is stored in the cache memory, the write data sent from the higher-level device is compared with the data at the address stored in the cache memory. A cache control method, wherein the write data is written to the magnetic disk only in a case. 2. A cache control method for a recording / reproducing apparatus having a cache memory in which a magnetic disk is used as a storage medium and a copy of a part of data stored in the magnetic disk is stored. When there is a write request for a plurality of addresses from among the plurality of addresses, for an address at which data is stored in the cache memory,
A cache for comparing write data of the address sent from the host device with data of the address stored in the cache memory, and writing the write data to the magnetic disk only when the comparison does not match; Control method. 3. A cache control method in a recording / reproducing apparatus having a cache memory in which a magnetic disk is used as a storage medium and a copy of a part of data stored in the magnetic disk is stored. For each of a plurality of addresses for which a write request has been issued from the cache memory, a cache hit determination process for determining whether or not data at the address is stored in the cache memory; and the data in the cache memory is stored in the cache hit determination process. For each of the addresses determined to have been written, a data comparison process of comparing write data for that address sent from the higher-level device with data of that address stored in the cache memory; and The cache hit judgment in the address Write the write data sent from the higher-level device to the magnetic disk only for the addresses for which data is determined not to be stored in the cache memory in the constant processing and for the addresses for which the comparison is determined to be inconsistent in the data comparison processing. A cache control method comprising a data write process. 4. A cache control device in a recording / reproducing apparatus having a magnetic disk as a storage medium and having a cache memory in which a copy of a part of data stored on the magnetic disk is stored. If the data at the address requested to be written from is stored in the cache memory, the write data sent from the higher-level device is compared with the data at the address stored in the cache memory. A cache control device for writing the write data to the magnetic disk only in a case. 5. A cache control device in a recording / reproducing apparatus having a magnetic disk as a storage medium and having a cache memory in which a copy of a part of data stored on the magnetic disk is stored. When there is a write request for a plurality of addresses from among the plurality of addresses, for an address at which data is stored in the cache memory,
Write data of the address sent from the host device is compared with data of the address stored in the cache memory, and write data is written to the magnetic disk only when the comparison does not match. Cache control device. 6. A cache control device in a recording / reproducing device having a magnetic disk as a storage medium and having a cache memory in which a copy of a part of data stored in the magnetic disk is stored. A cache memory control unit that determines, for each of a plurality of addresses for which a write request has been made from the cache memory, whether or not the data at that address is stored in the cache memory; and the cache memory data is stored in the cache memory control unit. For each of the addresses determined to be the same, a data comparison unit that compares the write data for the address sent from the higher-level device with the data for that address stored in the cache memory; and In the cache memory control unit in the address A control unit that writes the write data sent from the higher-level device to the magnetic disk only for the addresses determined not to be stored in the cache memory and the addresses determined to be mismatched by the data comparison unit; A cache control device comprising: