JPH02227754A - Disk cache control system - Google Patents

Abstract

PURPOSE:To shorten the data writing time and also to maintain the security of data by simultaneously writing data to a magnetic disk and a disk cache and starting the next process when the writing task is through with the disk cache. CONSTITUTION:When a write request is received from a CPU 1, a controller 4 starts to write data into a magnetic disk 3 and a disk cache 2 at one time. When the writing task is through to the cache 2, the controller 4 receives the next read/write requests and reads continuously data out of the cache 2 until the writing task is through to the disk 3. Thus a writing task is carried out to the disk 3 for each write request, and the data is read out of the cache 2 right after the data is written to the cache 2 even in a writing mode of the disk 3. As a result, the data writing time is shortened and at the same time the security of data is maintained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to disk cache control, and in particular is a control method suitable for shortening the access time during writing and maintaining the integrity of written data. [Technology] Conventional writing methods, as described in Japanese Patent Laid-Open No. 154649/1982, write the same data to the magnetic disk at the same time as writing to the disk cache when writing to a file on a magnetic disk (write-through). method).

In addition, as a method to shorten the writing time,
As described in No. 43685, when writing to the disk is completed, the process proceeds to the next step (write-back method).

[Problem to be solved by the invention]

In the above conventional technology, when writing to a magnetic disk, writing to the disk cache and writing to the magnetic disk are performed at the same time, and when both are completed, the writing process ends and the process moves on to the next process (write-through method). ), but the next input/output process cannot proceed until the writing to the magnetic disk is completed, so even if writing to the disk cache is fast, the input/output processing time is the same as a method without disk cache. The advantage of high-speed access of disk cache is not being taken advantage of.

Also, as a method to shorten the write time, there is a method (write-back method) in which the data is written only to the disk cache first, the writing is completed, the next processing is performed, and after a certain period of time the data is written from the disk cache to the magnetic disk. If a power failure occurs after writing to the disk cache but before writing to the magnetic disk is complete, the contents of the disk cache will be lost and the data that was determined to have been written will no longer remain on the magnetic disk.
There is a problem with data integrity.

An object of the present invention is to provide a disk cache control method that can shorten write time and maintain data integrity.

[Means to solve the problem]

The above purpose is to write the same data to the magnetic disk at the same time as writing to the disk cache when writing to the magnetic disk, and to end the write process and start the next process when the write to the disk cache is completed. This is achieved by performing such control.

[Effect]

In the write process, writing to the magnetic disk and writing to the disk cache are started at the same time, and when the write to the disk cache is completed, it is determined that the write process is completed and whether the next process is a write request or a read request.

If it is a write request, it waits until the writing process to the previous magnetic disk is completed.

If it is a read request, it is determined whether or not the requested data exists in the disk cache, and if the requested data does not exist, it waits for the completion of the write process to the previous magnetic disk. If it exists, read the data and continue with the next process.

That is, a request to read data existing in the disk cache continues until the writing process to the previous magnetic disk is completed.

By performing the above control, even if data is being written to the magnetic disk, reading processing of data existing in the disk cache will be performed immediately after the previous writing processing has been performed on the disk cache, so the disk cache High-speed access is also achieved during writing, reducing overall input/output time.

(Example〕 Hereinafter, one embodiment of the present invention will be described in detail.

FIG. 1 is a flowchart showing an example of a processing procedure when the present invention is applied to a disk cache system, and FIG. 2 is a block diagram showing the configuration of the disk cache system according to the present invention.

In FIG. 2, reference numeral 1 denotes a central processing unit having an input/output control section, which issues data read/write requests. 2
is a disk cache made of high-speed semiconductor memory and contains some of the same data as the magnetic disk. 3
is a magnetic disk with a recording head and contains all the data required by the central processing unit. 4 is a control device which is in charge of retrieving data from 2 and 3, recording, inspection 2 judgment, and controlling the operation of these devices, and controls the operation of devices 2 and 3 according to the program stored inside. do.

Next, the operation of each part shown in FIG. 2 will be explained based on the flowchart shown in FIG.

First, when there is a read/write request from the central processing unit 1 (step 101), the control unit 4
It is determined whether the write request is in progress (102)L, and if it has been completed, it is determined whether it is a read request or a write request like a normal disk cache system (103).
If it is a read request, read processing is performed from disk cache 2 or magnetic disk 3 (105°10
6) Proceed to the next process.

In the case of a write request, writing to the disk cache 2 and magnetic disk 3 is started simultaneously (107), and when writing to the disk cache 2 is completed (108), the next read/write request is received (101) and the data is transferred to the magnetic disk 3. The reading from the disk cache 2 (111) is repeated until the writing is completed (102).

The next process is a write request (109), or if the data you want to read is not in disk cache 2 (110)
), the next process waits until the previous write process to the magnetic disk 3 is completed.

〔Effect of the invention〕

According to the present invention, since the writing time to the magnetic disk is used to perform the subsequent processing of reading from the disk cache, there is an effect of shortening the input/output processing time. In this case, if there is a request for writing or reading from the magnetic disk as a process subsequent to writing, the process is interrupted. However, considering the nature of the disk cache system, in which read requests are several times more numerous than write requests, and the probability that the data to be read exists in the disk cache is extremely high, a sufficient effect can be expected.

From the perspective of data integrity, the process of writing to the magnetic disk is performed each time a write request is made to the magnetic disk, so in the event of a power failure, only the data being written is lost, so it is equivalent to a conventional magnetic disk. Reliability is ensured.

[Brief explanation of the drawing]

FIG. 1 is a flow chart showing an embodiment of the processing procedure of the present invention, and FIG. 2 is a block diagram of a disk cache system according to the present invention. 1...Central processing unit, 2...Disk cache,
3... Magnetic disk, 4... Control device.

Claims (1)

[Claims] 1. In a disk cache system consisting of a magnetic disk connected to a central processing unit and a disk cache, which employs a write-through method in which writing to files on the magnetic disk is performed in parallel to the magnetic disk and disk cache, It is determined that the write process has ended when writing to the disk cache is completed, and the time from that point until the end of writing to the magnetic disk is controlled so that reading from the disk cache is possible. A disk cache control method featuring: