Electrical computers and digital processing systems: memory – Storage accessing and control – Specific memory composition
Reexamination Certificate
1999-05-19
2001-12-11
Kim, Matthew (Department: 2186)
Electrical computers and digital processing systems: memory
Storage accessing and control
Specific memory composition
C711S111000, C711S112000, C711S129000
Reexamination Certificate
active
06330641
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method of controlling a magnetic disk device, which is capable of processing for rapidly writing and reading data on the magnetic disk device.
DESCRIPTION OF THE RELATED ART
For enhancing the processing efficiency of the magnetic disk device, a control unit is provided with a cache memory and data which is frequently accessed is stored therein and transferred from the cache memory upon request for the data without accessing to the magnetic disk device to shorten the period of processing time. It is known that selection of data to be stored in the cache memory and the manner of use of the cache memory give a large influence upon the degree of the enhancement in the processing speed.
As an effective method, a technique to minimize the access to the magnetic disk by dividing an object of the cache memory be managed into sector units is disclosed in Japanese Patent Kokai Publication JP-A-2-213962. Another technology attempting to prevent the lowering of the processing speed caused by deterioration of successive operation for the magnetic disk when data including an alternative area is read, by replacing the data which has been transferred to the alternative area based on a defect on the disk to the cache memory is disclosed in Japanese Patent Kokai Publication JP-A-5-66999.
SUMMARY OF THE DISCLOSURE
Serious problems which are related with the processing speed of the magnetic disk include retry processing for a read error. It may take a long extended period of time to complete the retry processing. The read error which requires the retry processing may occur due to the deterioration of the performance with lapse of time and conditions of application environment. Not all the read errors can be predicted. In the prior art control, the data which has been read for the retry processing is stored in the cache memory. While the data is stored in the cache memory, the data in the cache memory is used so that the efficiency is temporarily enhanced. The data is occasionally removed from the cache memory in the course of time due to using condition of the cache data. When the data which requires the retry processing is requested again, the processing speed is remarkably lowered due to the retry processing. Although processing to eliminate the read error is conducted by transferring data which frequently requests retry processing in the usual disk control, it takes an excessively extended period of time to complete the processing to transfer the data to an alternate area, and special processing is required. Accordingly, a number of devices are not capable of conducting such processing in the usual application environment.
Therefore, it might be conceived a method not to erase data which has been stored on a cache memory once as a result of retry. However, when a plurality of retry data are generated, the data would remain in an irregular manner if the data are left as they are. This would invite deterioration of the use efficiency of the cache memory and complication of the data management. For solving this problem, a new cache control such as rearrangement of control units and resident data would be required.
Therefore, it is an object of the present invention to provide a novel control method and system for shortening the processing period of time of the magnetic disk which is taken to complete the retry processing by making the data requiring the retry processing be resident in an appropriate unit, so that lowering of the processing performance of the magnetic disk device is suppressed.
Further, objects of the present invention will become apparent in the entire disclosure.
In accordance with one aspect of the present invention there is provided a novel method of controlling read/write of a magnetic disk device using a cache memory. The method of controlling the magnetic device is characterized in the following features:
Data of a block, for which has been required retry for reading data on the disk, is stored in an error area in the cache memory which is provided separately from a cache area, and if a block which is stored in the error area is included in a read request of data from a host unit, the block is read.
The method may further comprise the steps of:
on reception of a read request from the host unit, transferring the data to the host unit if the requested data is stored in the cache data area;
if no data is stored in the cache data area, calculating the range of data to be read, and reading from the magnetic disk device the data in the range up to the block concerned if there is registered data in the error block or reading data in the entire calculated range if there is no registered data to transfer the read data to the host unit and to store it in the cache area;
copying the data at a block address for which retry has been required of reading operation from the magnetic disk device to the error block data area if the retry has been conducted;
if data has been registered in the error block after reading from the magnetic disk device, subsequently selecting and transferring corresponding data from the error block data area to the host unit, and incorporating the data into the block concerned of the cache data area; and
repeating the steps of reading of data from the magnetic disk device and reading of data from the error block data area until reading of data in the range to be read is completed.
The method may further include the steps of:
writing to the magnetic disk device data which is transferred on reception of a write request from said host unit;
if the entire block address range in which the transferred data is accommodated is stored in the cache area, writing the transferred data to said magnetic disk device and replacing the data in the corresponding cache area by the transferred data;
if the block which has been registered in the error area is included in the write requested range and write data does not remain in the cache area, canceling the registration of a block included in the range from said error area to the write area; and
if the block which has been registered is included in the error area in the write requested range and write data remains in the cache area, selecting corresponding data from the data in the cache area and copying the data to corresponding area of the error area.
According to a second aspect of the present invention there is provided a control apparatus of the magnetic disk device, particularly, an apparatus for controlling read/write of a magnetic disk device, including a cache memory. The control apparatus of the magnetic disk device comprises a host unit interface, magnetic disk device interface, cache memory interface, cache memory, control system and recording medium. The host unit interface is adapted to transfer read/write data and to exchange control information between the host unit interface and the host unit. The magnetic disk device interface is adapted to transfer read/write data and to exchange control information between the magnetic disk device interface and the magnetic disk device. The cache memory interface is adapted to transfer read/write data and to exchange control information between the cache memory interface and the cache memory. The cache memory comprises a cache memory area which is used as an inherent disk cache and an error area for holding and controlling data of a block for which retry has been done, each block including a control table and data area. The control system controls the operation of read/write of data from/to the magnetic disk device on reception of an instruction from the host unit in response to an operation command in accordance with a program. The recording medium records thereon a control program for controlling read/write of data from/to said magnetic disk device in the control system.
The data of the magnetic disk device which is treated as cache data may be stored in the cache data area, information used for controlling the use condition of the cache memory may be stored in the cache control table. The data of the block which could
Foley & Lardner
Kim Matthew
NEC Corporation
Vital Pierre M.
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