GB2233481A

GB2233481A - Magnetic disk storage with cache

Info

Publication number: GB2233481A
Application number: GB9013319A
Authority: GB
Inventors: Masayuki Urabe
Original assignee: Tokico Ltd
Current assignee: Tokico Ltd
Priority date: 1989-06-20
Filing date: 1990-06-14
Publication date: 1991-01-09
Also published as: DE4019684A1; GB9013319D0; JPH0322156A

Abstract

A magnetic disk storage apparatus which can be connected to a host computer as an external storage apparatus is provided with a magnetic disk, a cache for temporarily storing data transferred from said magnetic disk, a first data transfer device for transferring data from the magnetic disk to the cache on first read command from the host computer, a device for setting a cache function flag to indicate that data are stored in the cache, on a first read command from the host computer, and a second data transfer device for transferring data from the cache to the host computer, when the cache function flag is set to indicate that data are stored in the cache, on a second read command from the host computer. <IMAGE>

Description

MAGNETIC DISK STORAGE APPARATUS

Background of the Invention

Field of the Invention

The present invention relates to a magnetic disk storage apparatus which contains data processing functions, especially cache functions, that is to say, faster-access buffer storage.

Prior Art

Recently, various kinds of intelligent magnetic disk storage apparatus containing a controller have been provided for the purpose of reducing the load of the host computer and increasing the throughput of the system. SCSI (Small Computer System Interface), useful in multitasking has been provided with the above mentioned apparatus as one of the interfaces connecting the above mentioned controller and host computer.

The above described magnetic disk storage apparatus executes data read processing, replying to a read command from the host computer as follows:

the host computer (a) reads the file registration information, called the directory, from the memory connected to the host computer, and (b) fetches the read address of file from the directory, and (c) reads the desired file from the above described apparatus by means of the read address fetched from the directory.

The procedure of accessing the desired file as above described was needed for the control of files in the system.

However, the access procedure was very complicated. and the complexity of the procedure prevented an increase in the throughput of the data processing system.

Summary of the Invention

In consideration of the above described problem, it 1 is an object of the present invention to provide a magnetic disk storage apparatus which is capable of easier and faster data access, according to a read command from the host computer, thereby increasing the throughput of the data processing system.

In an aspect of the present invention, there is provided a magnetic disk storage apparatus connected with a host computer, the apparatus comprising: a magnetic disk for storing data; a cache for temporarily storing data transferred from the magnetic disk; a cache function flag for Indicating whether data are stored In the cache or not; a first data transfer device for transferring data from the magnetic disk to the cache, according to a first read command from the host computer; a flag setting device for setting the cache function flag to indicate that data are stored in the cache, according to a first read command from the host computer; and a second data transfer device for transferring data from the cache to the host computer when the cache function flag is set to indicate that data are stored in the cache, according to a second read command from the host computer.

The present invention, when data accessing from the host computer, if the cache function flag is set, transfers data from the cache to the host computer, without directly accessing the data on the magnetic disk.

Therefore, the present invention can achieve faster data read processing and an increase in the throughput of the data processing system.

Brief Description of the Drawings

Fig.1 is a block diagram showing the summary structure of a magnetic disk storage apparatus in accordance with a preferred embodiment of the present invention.

Fig. 2 and Fig. 3 are flow charts showing the operation of the central processing unit in the magnetic disk storage apparatus shown in Fig. 1.

2 1 Detailed Description of the Preferred Embodiment

In the following section, a preferred embodiment of the present Invention will be described with reference to the drawings.

Fig.1 is a block diagram showing the summary structure of a magnetic disk storage apparatus in accordance with a preferred embod iment of the present Invention. As shown in this figure, the magnetic storage apparatus Is composed of central processing unit (hereafter referred to as CPU) 1, bus 2, memory 3, drive circuit 4, 110 interface 5, external bus 6 and host computer 7. The above-mentioned CPU 1 is the controlling center of the the magnetic storage apparatus and contains various kinds of facilities for instruction execution, timing functions, and other machine-related functions to accomplish the above mentioned SCSI functions.

By means of bus 2, CPU 1 is connected to memory 3, drive circuit 4 and I/0 interface 5. Memory 3 stores various kinds of data, such as the control program, the processing program and so on, that CPU 1 requires to perform a given job. Memory 3 also contains a faster-access buffer storage, called a cache and a cache function flag for showing whether buffer data is stored on the cache or not. The above mentioned cache has a storage capacity equivalent to the amount of data transferred in one to two seconds. The cache is appropriately constituted by RAM (Random Access Memory). Drive circuit 4 drives and revolves the magnetic disk. All communication between CPU 1 and host computer 7 takes place by means of I/0 interface 5. 1/0 interface 5 connects with host computer 7 by means of external bus 6.

In the following section, the operations carried out by CPU 1 will be described with reference to Fig. 2 and Fig 3. (a) The procedure of the work requested by a VENDOR UNIQUE COMMAND (Fig. 2) Fig. 2 is a flow chart showing the procedure of the work of CPU 1 requested by VENDOR UNIQUE COMMAND. Here, this VENDOR UNIQUE COMMAND means a command able to be optionally defined by users.

As shown hereinafter, in this embodiment, the above 3 mentioned VENDOR UNIQUE COMMAND functions as a command requesting a data transfer from the magnetic disk to the cache.

if power has been supplied to CPU 1, CPU 1 starts operation. First of all, in step SA1, CPU 1 judges whether or not a VENDOR UNIQUE COMMAND has been accepted from host computer 7. Here, when the result of the judgment is [NO], that is to say, when a VENDOR UNIQUE COMMAND has not been entered, CPU 1 goes to step SA2, and therein performs the work requested by an ordinary command. After processing in step SA2, CPU 1 finishes the routine work shown in Fig. 2. On the other hand, in step SA1, when [YES] is determined as the result of the judgment, that is to say, when a VENDOR UNIQUE COMMAND has been entered, CPU 1 moves to step SA3, and sets the above mentioned cache function flag to the "H" level. Here, the OHn level to which the cache function flag Is set means that the cache function has been reserved by host computer 7. Next, in step SA4, CPU 1 accepts a reserved address from host computer 7. Here, a reserved address means the address of the data that host computer 7 requires to be transferred from the magnetic disk to the cache. Therefore, in step SAS, CPU 1 addresses according to the above mentioned reserved address and reads the data from the magnetic disk. Last, In step SA6, the data read from the magnetic disk is transferred to and stored in the cache.

Thus, the "H" level to which the cache function flag is set indicates that the data corresponding to a reserved address are stored in the cache.

With the completion of the processing in step SA6, the work requested by the above mentioned VENDOR UNIQUE COMMAND terminates.

(b) The procedure of the work requested by a READ COMMAND (Fig. 3) Fig. 3 Is a flow chart showing the procedure of the work requested by a READ COMMAND. First of all, in step SB1, CPU 1 judges whether or not a READ COMMAND has been received from host computer 7. Here, when [NO] is the 4 result, that is, when a READ COMMAND has not been entered, CPU 1 goes to step SB2. In step SB2, the work requested by an ordinary command is performed. After processing in step SB2, CPU 1 finishes the routine work shown in Fig. 3. on the other hand, In step SB1, when [YES] Is the result, that is, when a READ COMMAND has been entered, CPU 1 goes to step SB3. In step SB3, CPU 1 examines whether or not the cache function flag Is set to the wHO level, that Is, whether or not cache functions have already been reserved. Here, if [NO] Is determined to be the result of the examination, CPU 1 goes to step SB6, reads data directly from the magnetic disk and finishes the data read processing shown in Fig. 3. On the other hand, in step SB3, if [YES] is determined, CPU 1 proceeds to step SB4. In step SB4, CPU 1 checks whether or not the read address (transmitted from host computer 7 in this READ COMMAND processing) and the reserved address (transmitted from host computer 7 in the earlier VENDOR UNIQUE COMMAND processing) are the same. When [No] is determined to be the result of this check, that is to say, when the read address is not the same as the reserved address, CPU 1 goes to step SB6, reads data directly from the magnetic disk and finishes this data read processing. On the other hand, in step SB4, when [YES] is determined, that is to say, when the read address Is the same as the reserved address, CPU 1 moves to step SB5. In step SB5, CPU 1 transmits the cache data to host computer 7 and finishes this data read processing.

While one preferred embodiment of the present invention Is described above, It is not intended to limit the present invention to this embodiment.

CLAM 1. A magnetic disk storage apparatus suitable for being connected to a host computer and used as a external storage apparatus of said host computer, said magnetic disk storage apparatus being characterized by comprising:

(a) a magnetic disk for storing data; (b) buffer storage for temporarily storing data transferred from said magnetic disk; (c) a buffer data flag for Indicating whether data are stored In said buffer storage or not; (d) a first data transfer means for trasferring data from said magnetic disk to said buffer storage, according to a first read command from said host computer; (e) a flag setting means for setting said buffer data flag to indicate that data are stored in said buffer storage, according to a first read command from said host computer; and (f) a second data transfer means for transferring data from said buffer storage to said host computer, when said buffer data flag is set to indicate that data are stored in said buffer storage, according to a second read command from said host computer.

2. A magnetic disk storage apparatus according to claim 1 above, which is further characterized by having an input/output interface for communicating with said host computer.

3. A magnetic disk storage apparatus according to claim 1 above, which is further characterized by including a central processing unit, whereby said first data transfer means and second data transfer means are constituted.

4. A magnetic disk storage apparatus according to claim 1 above, which is further characterized by comprising said buffer storage, which consists of RAM.

6 9 5. A magnetic disk storage apparatus according to either of the claims 1 or 3 above, which is further characterized by including; a first recognizing means for recognizing whether or not said first read command has been accepted from said host computer, a second recognizing means for recognizing whether or not said second read command has been accepted from said host computer, and a third recognizing means for recognizing whether or not said buffer data flag is set to indicate that data are stored in said buffer storage.

6. A magnetic disk storage apparatus according to claim above, which is further characterized by including said second recognizing means; said second recognizing means recognizes whether or not the second read address corresponding to said second read command is the same as the first read address corresponding to said first read command, and when the result of this judgment is [YES], recognizes that said second read command has been accepted from said host computer.

7. A magnetic disk storage apparatus according to claim 5 above, which is furtehr characterized by including a central processing unit, whereby said first recognizing means, second recognizing means and third recognizing means are constituted.

8. A magnetic disk storage apparatus according to claim 6 above, which is further characterized by including a central processing unit, whereby said first recognizing means, second recognizing means and third recognizing means are constituted.

9. The magnetic disk storage apparatus substantially as herein described with reference to and as shown in the accompanying drawings.

Published 1991 at The Patent Office. State House, 66171 High Holbom. London WC I R 4TP. Further copies may, be obtained from The Patent Office Sales Branch. St Mary Cray. Orpington. Kent BR5 3RD Printed by Multiplex techniques ltd. St Mary Cray. Kent, Con 1187