Access control method for shared duplex direct access storage device and computer system therefor
First Claim
1. A DASD access control method for use in a computer system comprising a plurality of processing units, a memory connected to said plurality of processing units and duplex direct access storage devices (hereinafter "DASD'"'"'s") accessible by said plurality of processing units, said duplex DASD'"'"'s comprising a first DASD for storing a plurality of data groups in addressable storage locations therein and a second DASD for storing a plurality of data groups in addressable storage locations therein, said first DASD and said second DASD including identical contents and one-to-one correspondence between the data groups stored in corresponding storage locations therein, wherein each one of said data groups of said first DASD and each corresponding one of said data groups of said second DASD form a data group set and are accessible as a logical unit by one of said plurality of processing units, said DASD access control method comprising the steps of:
- (a) storing information in said memory device for identifying the invalidity of data groups in which an irrecoverable failure has occurred within said plurality of data groups stored in said first DASD and said second DASD;
(b) judging whether one data group of a data group set stored in said first DASD and said second DASD and accessible by one of said plurality of processing units previously had an irrecoverable failure based on said stored information in said memory, when said one data group is accessed;
(c) accessing said one data group of said data group set when said step (b) results in a determination that said one data group does not have an irrecoverable failure; and
(d) stopping access to said one data group of said data group set when said step (b) results in a determination that said one data group has an irrecoverable failure.
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Accused Products
Abstract
Disclosed is a DASD access control method including storing information for identifying one data group in which an irrecoverable failure has occurred in the plurality of data groups stored in each of the first and second DASDs constituting the duplex DASD pair. A judgment is determined based on the stored information as to whether one data group has an irrecoverable failure which has occurred when the one data group held in either one of the first and second DASDs constituting the duplex DASD pair is accessed by one of the plurality of processing units. Access is allowed to the one data group in the one DASD by the one processing unit when the judgment results in that the one data group has no irrecoverable failure which has occurred therein. Finally, the access is stopped to the one data group when the judgment results in that the one data group has an irrecoverable failure which has occurred therein.
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Citations
21 Claims
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1. A DASD access control method for use in a computer system comprising a plurality of processing units, a memory connected to said plurality of processing units and duplex direct access storage devices (hereinafter "DASD'"'"'s") accessible by said plurality of processing units, said duplex DASD'"'"'s comprising a first DASD for storing a plurality of data groups in addressable storage locations therein and a second DASD for storing a plurality of data groups in addressable storage locations therein, said first DASD and said second DASD including identical contents and one-to-one correspondence between the data groups stored in corresponding storage locations therein, wherein each one of said data groups of said first DASD and each corresponding one of said data groups of said second DASD form a data group set and are accessible as a logical unit by one of said plurality of processing units, said DASD access control method comprising the steps of:
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(a) storing information in said memory device for identifying the invalidity of data groups in which an irrecoverable failure has occurred within said plurality of data groups stored in said first DASD and said second DASD; (b) judging whether one data group of a data group set stored in said first DASD and said second DASD and accessible by one of said plurality of processing units previously had an irrecoverable failure based on said stored information in said memory, when said one data group is accessed; (c) accessing said one data group of said data group set when said step (b) results in a determination that said one data group does not have an irrecoverable failure; and (d) stopping access to said one data group of said data group set when said step (b) results in a determination that said one data group has an irrecoverable failure. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. A DASD access control method for use in a computer system comprising a plurality of processing units, and duplex direct access storage devices (hereinafter "DASD'"'"'s") accessible by said plurality of processing units, said duplex DASD'"'"'s comprising a first DASD for storing a plurality of data groups in addressable storage locations therein and a second DASD for storing a plurality of data groups in addressable storage locations therein, said first DASD and said second DASD including identical contents and one-to-one correspondence between the data groups stored in corresponding storage locations therein, wherein each one of said data groups of said first DASD and said corresponding one of said data groups of said second DASD form a data group set and are accessible as a logical unit by one of said plurality of processing units, said DASD access control method comprising the steps of:
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(a) storing reserve flags exclusively in a random access memory which is commonly accessible by said plurality of processing units, said stored reserve flags respectively corresponding to said plurality of data groups stored in said first DASD and said second DASD, wherein each one of said reserve flags indicates whether the corresponding data group is in a reserved state; (b) reserving said random access memory for one of said plurality of processing units when said one processing unit is to access one of said plurality of data groups of a data group set stored in said first DASD and said second DASD; (c) subsequently reading one reserve flag corresponding to said one data group of a data group set from said random access memory; (d) rewriting said one reserve flag into a reserve indicating state to reserve said one data group of a data group set when said one reserve flag which is read out is not in said reserve indicating state; (e) releasing the reserved state of said random access memory; and (f) accessing said one data group. - View Dependent Claims (13, 14, 15)
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16. A computer system comprising:
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(a) a plurality of processing units; (b) a first direct access storage device connected to said plurality of processing units for storing a plurality of data groups in addressable storage locations therein, wherein each one of said data groups are individually accessible as a logical unit by one of said plurality of processing units; (c) a random access memory which is commonly accessible by said plurality of processing units for storing only a plurality of pieces of control information respectively corresponding to each of said plurality of data groups for controlling access from said plurality of processing units to said data groups; and (d) an access control circuit for controlling access from said plurality of processing units to said random access memory, wherein said plurality of processing units and said random access memory are connected to said access control circuit, said access control circuit including; (d1) reserve means for reserving said random access memory for one of said processing units in response to a random access memory reserve request, and for releasing the reserved state of said random access memory in response to a random access memory reserve releasing request; and (d2) control means connected to said reserve means for controlling access to one of said pieces of control information in said random access memory requested by a request issued by one of the processing units, depending on whether said random access memory is in a reserved state with respect to said one processing unit. - View Dependent Claims (17, 18, 19, 20, 21)
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Specification