Electrical computers and digital processing systems: memory – Storage accessing and control – Specific memory composition
Reexamination Certificate
2000-07-18
2003-10-07
Peikari, B. James (Department: 2186)
Electrical computers and digital processing systems: memory
Storage accessing and control
Specific memory composition
C711S111000, C714S006130, C714S006130
Reexamination Certificate
active
06631443
ABSTRACT:
BACKGROUND OF WE INVENTION
The present invention relates to the control of the execution of a load for a storage, particularly the control of parallel processing with respect to input and output for disk drives.
In Japanese Patent Laid-Open No. 114947/1985, a double write control has a cache (hereinafter referred to simply as a cache). Two disks, called double write disks, are each written with the same data. A control unit processes an input output request from a CPU for one of the two disk units. In the case of receiving a read request (input request) from the CPU, the control unit executes the request as it is. In the case of receiving a write request (output request) from the CPU, data is written in a specific one of the double write disks and at the same time the same data is written in the cache. At a later time, making use of available processing time when the control unit and disks have nothing else to do, the control unit writes the same data from the cache into the other disk unit, which is called a write after process. In this manner, the same data is written to each disk unit of the double write disk units.
In Japanese Patent Publication No. 28128/1986, there is disclosed a double filing control for load distribution with respect to double write disk units. There is no write after process. The control is designed to achieve a higher processing speed by selecting an inactive disk unit, among the disk units, when an input/output request is received. An inactive disk unit will be defined herein as a disk unit that is currently not undergoing any disk accessing, that is not undergoing any read or write operation.
In a thesis found in the Information Process Institute Bulletin “Nishigaki et al: Analysis on Disk Cache Effects in a Sequential Access Input Process”, Vol. 25, No. 2, pages 313-320 (1984), there is disclosed with respect to a single disk unit a read ahead control having a cache, which involves the staging, in the cache, data not requested by the CPU but which will be requested in an instruction shortly following the current instruction. This staging process is executed by the control unit independently of any execution of an input/output request from the CPU.
SUMMARY
It is an object of the present invention to solve problems, analyzed below, that the inventors have found with respect to the above-noted controls.
Japanese Patent Laid-Open No. 114947/1985 does not give any attention to a potential advantage of the double write disk system, namely that a plurality of disk units can be controlled by the control unit, but instead the document discloses that the CPU input/output request is limited to one specific disk unit as requested by the CPU. Therefore, even though there is another disk unit that may be inactive, the request cannot be fulfilled by the control unit if the CPU requests the one specific disk unit that happens to be active at the time. The disk unit is considered active when it is undergoing some type of input/output process.
On the other hand, Japanese Patent Publication No. 28128/1986 has excellent performance by selecting an inactive disk unit by the control unit for an input/output request from the CPU. However, this is applied to the double write function by utilizing a cache without a write after control, and therefore it's reliability is lowered. This is due to the high possibility that write data is received from the CPU that is applicable to all the disk units, but is stored in the cache without being immediately written to a disk unit. Therefore, if power failure occurs in the cache in combination with the breakdown of any one of the disk units, the write data received from the CPU is lost.
Furthermore, in the case of a control unit having a cache, the control unit can execute an input/output between the cache and the disk unit independently of an input/output request from the CPU, as disclosed in the thesis in the Information Process Institute Bulletin, mentioned above. In view of this, the inventors think that attention should be given to the possibility that a plurality of disk units can be selected for an input/output process by the control unit independently of an input/output request from the CPU.
Japanese Patent Laid-Open No. 135563/1984 does not have any relation to the double write system. This patent relates to the cache disk control unit with a write after control. The disk control unit stores the write data received from the CPU to both the cache memory and the non-volatile memory. The write data in the a memory is written to the disk unit by utilizing a write after process. Therefore, the write request issued by the CPU can be processed at high speed without accessing the disk unit, moreover, this can realize the highly reliable write after process. If the write data in the cache memory is lost because of the breakdown of the cache memory, the write data remains in the non-volatile memory. However this patent does not relate to the double write function.
Specifically, the present invention relates to the control for providing a write after process using a cache so that the same data may be written to a disk unit group, comprising one or more disk units. If the disk unit group comprises one disk unit, the disk unit has a plurality of disks on each of which is written the same data. If the disk unit group comprises a plurality of disk units, each disk unit may have one or more disks, with the same data being written to each disk unit of the group.
The object of the present invention is to provide control for improving parallel execution of input/output processes by distributing the processes among disk units in the disk unit group, for distributing the load of the input/output processes under the control of the control unit.
To better understand the present invention, input/output processes, which the control unit executes between the control unit and the disk units can be classified into four kinds, as follows:
(1) A write request received from the CPU, which requires access to a disk unit.
(2) A read request received from the CPU, which requires access to a disk unit.
(3) A staging process performed independently of an input/output request from the CPU (that is independently of a read request or a write request from the CPU), which transfers the data from a disk unit to a cache.
(4) A write after process executed between the control unit and a disk unit.
Of the above mentioned four kinds, the write after process is not an object for load distribution, as will be explained later. The write after process is executed, with respect to a disk unit group, for all of the disk units other than those to which the same data has already been written, when a write request received from the CPU is executed. Therefore, there is no freedom for selecting a disk unit which should be used to execute the write after process. Therefore, in the above four processes, the first three processes are objects for load distribution.
In the present specification, two kinds of load distribution according to the present invention will be discussed.
In the first kind of load distribution, the control unit selects a disk unit among the disk units that are inactive when the control unit executes an input/output process involving either the second (read) or third (staging) kind of process When a disk unit should be selected for a write request from the CPU, which requires access to the disk unit according to the first type of the four mentioned input/output processes, the control unit selects a specific disk unit in the disk unit group for the immediate writing of data.
In the second kind of load distribution, when the control unit selects a disk unit for an input/output process of the first type, that is for the write request received from the CPU which requires access to a disk unit, a specific disk unit in the disk unit group is selected. When a disk unit is selected to execute an input/output process of the second and third types (read and staging), a disk unit other than the above-mentioned specific disk unit is selected, preferably arbitrarily.
Th
Asaka Yoshihiro
Honma Shigeo
Kitajima Hiroyuki
Kuwahara Yoshiaki
Satoh Takao
Mattingly Stanger & Malur, P.C.
Peikari B. James
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