Abstract:
Disk units operable under control of different disk control units hold the same data. Under circumstances in which data is duplexed, when data is duplexed again after data that is generally saved as backup data was accessed for reading and writing, in order to efficiently duplex data, update places of both original data and sub-data updated during the duplexing of data is interrupted are registered on an access information management table of an original disk control unit. When the original disk control unit receives a duplexing resume command, the duplexing of data may be efficiently reorganized by copying original data corresponding to an access place produced during the duplexing is interrupted from information of the access information management table to the backup data or by copying the backup data to the original data.

Description:
This is a continuation of application Ser. No. 10/348,783 filed 23 Jan. 2003, now U.S. Pat. No. 6,742,093, which is a continuation of application Ser. No. 09/982,935 filed 22 Oct. 2001, now U.S. Pat. No. 6,615,328, which is a continuation of application Ser. No. 09/256,859 filed 24 Feb. 1999, now abandoned, the contents of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a multiplexed data memory system in which an external memory control unit which receives a write command from a host unit and which memorizes the received write command in an external memory unit under its control as original data writes the same data as that original data in the external memory unit operable under different external memory control units as backup data. More particularly, the present invention relates to a multiplexed data reorganizing system capable of effectively utilizing backup data and which is also able to efficiently reorganize the duplexing of original data obtained after backup data was used and the backup data, and relates to a subsystem for carrying out this system. 
     In a multiplexed data memory system in which data used in a host unit such as a host computer is multiplexed and held by a plurality of external memory units, e.g. original external memory unit and sub-external memory unit, as a method of holding the multiplexing of data between the original external memory unit and the sub-external memory unit, there are generally known technologies disclosed in Japanese Published Unexamined Patent Application No. Hei 6-214853, Japanese Published Unexamined Patent Application No. Hei 7-6099, Japanese Patent No. 2509460 and Japanese Translation of PCT Application No. Hei 8-509565. According to the method disclosed in the above-mentioned technologies, an original external memory unit and sub-external memory unit are provided under control of different external memory control units, the original external memory control unit and the sub-external memory control unit are connected via an interface cable and a write command received at the original-side external memory control unit is issued to the sub-side external memory control unit, thereby resulting in the multiplexing of data of the original external memory unit and the sub-external memory unit being maintained. 
     In such multiplexed data memory system, as a method of reorganizing the multiplexing after the multiplexing is interrupted, there is known a method of copying only an update place of an original external memory unit which is interrupted in multiplexing to a sub-side external memory unit, i.e. so-called difference copy. 
     In this difference copy, data of the sub-side external memory unit is generally used as backup data of the original-side external memory unit. During data is duplexed, a write access and a read access are generally inhibited from a standpoint of coincidence of original data and sub-data. 
     SUMMARY OF THE INVENTION 
     Recently, although a demand of effectively utilizing backup data increases from a standpoint of increasing an efficiency of a business, an inefficient procedure should be unavoidably made in order to reorganize the multiplexing after the access on the backup data was ended. 
     When backup data is temporarily used as test program data by utilizing the duplexed data memory system, for example, or when backup data of data of a certain time point is obtained from a sub-side external memory unit and saved in other memory medium, further when a trouble occurs the sub-side external memory unit and when the sub-side external memory unit is accessed in order to execute a program for restoring such trouble, if the duplexing of data should be released and the duplexing of data should be formed again, then all data of the original-side external memory unit should be copied to the sub-side external memory unit. 
     However, in this case, when a difference of several tracks at most occurs in the original-side and sub-side data due to the access on the sub-side external memory unit, according to the above-mentioned method of reorganizing the multiplexed data, there is then the problem that an efficiency of re-arrangement is not excellent. 
     Also, when a business is temporarily shifted to the sub-side system, the duplexed state of data should be released. When the business is again returned to the original-side system, the old sub-side system is provisionally set in the original-side system and the old original-side system is provisionally set in the sub-side system thereby duplexing the data. Further, the duplexed state is released, the provisional sub-side system is returned to the original system, the provisional original-side system is returned to the subsystem and the business is resumed in the inherent original-side system. Such a complex procedure should be executed. 
     That is, in the conventional multiplexed data memory system, the multiplexed state should be released in order to access the backup data. When the multiplexing is reorganized after the accessing was ended, an inefficient procedure requiring the initialization should be executed. 
     A problem of the present invention is that, under circumstances in which the multiplexing of data is organized, after read and write accessing was made on data generally saved as backup data, the multiplexing of data may be reorganized efficiently. 
     A fundamental feature of the present invention lies in that, under circumstances in which the multiplexing of data is organized, after read and write accessing was made on data generally saved as backup data, when the multiplexing of data is organized again, the multiplexing may be reorganized efficiently by copying only the update places obtained by the access from the original system to the subsystem or from the subsystem to the original system. 
     A feature of the multiplexed data processing system according to the present invention has a function to issue an original disk control unit write command to the sub-disk control unit which controls the backup data in the multiplexed data memory system in which disk units which are under control of different disk control units have the same data. 
     Thus, update places of original and sub data updated during data is multiplexed are registered on the access information management table of the original disk control unit as access information. When the original disk control unit receives a duplexing resume command, it becomes possible to efficiently reorganize the duplexing by copying original data corresponding to the access place occurred in the duplexing interruption from the information of the access information management table to the backup data or copying the backup data to the original data. 
     Also, a feature of the multiplexed data processing system according to the present invention is that it has a function to register access places on the access information management table. 
     The duplexing re-arrangement in the duplexed data memory system according to the present invention and its action will be described concretely as follows. 
     Initially, each time the write access occurs in the backup data obtained during the duplexing is interrupted in the channel command analyzing section of the subsystem, the access place is registered on the access information management table. 
     Then, when the channel command analyzing section receives an access end command relative to the backup data, the channel command analyzing section reports it to the original system. The original system reads out information from the access information management table of the subsystem, merges the read-out information to the access information of the original system and registers the merged information on the access information management table. 
     When the channel command analyzing section of the original system receives the duplexing resume command, the access information management table is checked, and a write command or a read command of data of the access place is issued to the subsystem, thereby reorganizing the duplexing. 
     The feature of the present invention will be described more in detail. The present invention is a subsystem comprising means for recognizing whether or not the access of the original side external memory control unit on the sub-side external memory unit is started or ended and means for judging which data of the original-side and sub-side external memory control units should be used as original data when the duplexing of data is reorganized after the backup data was updated and wherein the original-side and sub-side external memory control units include means for recognizing the access situation of the backup data. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram showing a data processing system according to an embodiment of the present invention; 
         FIG. 2  is a block diagram showing inside arrangements of original and sub-disk control units in  FIG. 1 ; 
         FIG. 3  is a table showing a correspondence between the state contents registered on a state management table and their abbreviations; 
         FIG. 4A  is a flowchart showing a flow of a processing executed by a sub-disk control unit until a state management table is set and an access information management table is set after the access occurred in the sub-disk unit; 
         FIG. 4B  is an example of an access registration processing {circle around ( 1 )} of  FIG. 4A ; 
         FIG. 4C  is another example of an access registration processing {circle around ( 1 )} of  FIG. 4A ; 
         FIG. 5A  is a flowchart showing a flow of a processing executed by the sub-disk control unit until access information is reported to the original disk control unit after the access to the sub-disk unit was ended; 
         FIG. 5B  is an example of an access information reporting processing {circle around ( 2 )} of GIG. 5 A; 
         FIG. 5C  is another example of an access information reporting processing {circle around ( 2 )} of GIG. 5 A; 
         FIG. 6A  is a flowchart showing a flow of a processing executed by the original disk control unit until access information of the sub-disk unit is obtained after the access end report relative to the sub-disk unit was received; and 
         FIG. 6B  is an example of an access information registration processing {circle around ( 3 )} of  FIG. 6A ; 
         FIG. 6C  is another example of an access information registration processing {circle around ( 3 )} of  FIG. 6A ; 
         FIG. 7A  is a flowchart showing a flow of a processing executed in the original disk control unit when the duplexing is resumed from its interruption; 
         FIG. 7B  is a flowchart showing the flow of a processing after the processing {circle around ( 4 )} of  FIG. 7A . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     An embodiment in which the present invention is applied to the duplexed data memory system will be described below. 
       FIG. 1  of the accompanying drawings is a block diagram showing a duplexed data memory system according to an embodiment of the present invention. As shown in  FIG. 1 , this duplexed data memory system comprises an original system composed of a main memory unit  1 , a original channel unit  2 , an original disk control unit  3  serving as an external memory control unit and an original disk unit  4  serving as an external memory unit and a subsystem composed of a main memory unit  5 , a subchannel unit  6 , a subdisk control unit  7  and a subdisk unit  8  similarly to this original system. The original channel unit  2  and the original disk control unit  3 ; and the subchannel unit  6  and the subdisk control unit  7  are connected together by interface cables  9  and  10 . Also, the original disk control unit  3  and the subdisk control unit  7  are connected by an interface cable  11 . 
     Incidentally, the main memory unit  1  and the original channel unit  2  are connected to a part of a host unit (not shown) or the host unit. 
       FIG. 2  shows the internal arrangements of the original disk control unit  3  and the subdisk control unit  7 . 
     As shown in  FIG. 2 , the original disk control unit  3  includes a channel command analyzing section  30 , a subdisk control unit command issuing section  31 , a subdisk control unit command analyzing section  32 , a state management table  33  for managing the state of a duplexing forming disk unit and an access information management table  34  for registering access places of original and sub-disk units obtained during the duplexing is interrupted. 
     Similarly, the subside disk control unit  7  includes a channel command analyzing section  36 , an original disk control unit command issuing section  37 , an original disk control unit command analyzing section  38 , a state management table  39  for memorizing the same information as that of the state management table  33  of the original disk control unit and an access information table  40  for memorizing access places of the subdisk unit obtained during the duplexing is interrupted. 
     As disk units used as original and sub-disk units, there are generally used magnetic disks, and any disk units may be used so long as they may be used as recording media such as a magnetic tape and a DVD. 
       FIG. 3  shows contents registered on the state management tables  33 ,  39  and their abbreviations. A state  1  shows the state in which the duplexed data memory system shown in  FIG. 1  is used in the duplexing circumstances and data of the original system and the subsystem are coincident with each other. 
     A state  2  shows the state in which the duplexed data memory system shown in  FIG. 1  is interrupted in use under the duplexing circumstances and data of the original system is updated. 
     Further, a state  3  shows the state in which the duplexed data memory system shown in  FIG. 1  is interrupted in use under the duplexed data circumstances and the write access is made on the subsystem. 
     The processing operation in the embodiment of the present invention will be described in accordance with the flowcharts of  FIGS. 4 to 7 . In  FIGS. 4 to 7 , “state  1 ”, “state  2 ” and “state  3 ” shown as the states registered on the state management table are those shown in  FIG. 3 . The present invention shown in  FIGS. 1 to 3  will be described in detail with reference to  FIGS. 4 to 7 . 
       FIG. 4A  shows a flow of processing executed in the subdisk control unit  7  until the state management table  39  is set and the access information management table  40  is set since the access occurs in the sub-disk unit  7 . 
     In  FIG. 4A , if the command received at the channel command analyzing section  36  of the sub-disk unit  7  is the access to duplexed data (step  100 ) and is also the write access (step  110 ), then the state management table  39  is checked. Then, the state is the duplexing (“state  1 ”) (step  120 ), then a command of the requested write access is rejected (step  130 ). 
     If the state is the duplexing interruption (“state  2 ”) (step  140 ), then the duplexing interruption write access state (“state  3 ”) is registered on the state management table  39  (step  150 ), and such state is reported to the original disk control unit  3  (step  160 ) by a dedicated command. Also in the original disk control unit  3 , the received state is similarly registered on the state management table  33 . 
     With respect to the registration processing {circle around ( 1 )} of access information on the sub-disk unit  8  in  FIG. 4A , as shown in  FIG. 4B , write access place information may be registered on the access information management table  40  (step  170 ). Alternatively, as shown in  FIG. 4C , the access information may be reported to the original disk control unit  3  by a dedicated command (step  180 ). 
     When the access information registration processing shown in  FIG. 4B  is realized, after the access to the backup data was ended, the disk control unit for controlling original data collectively reads out update place information of backup data from the disk control unit which controls the backup data. 
     On the other hand, when the access information registration processing shown in  FIG. 4C  is realized, after the access to the backup data was ended, the disk control unit for controlling backup data collectively reports update place information of backup data to the disk control unit which controls original data. 
     In any cases, the original disk control unit  3  merges received access information to access information relative to the original disk unit  3 , and registers merged access information on the access information management table  34 . 
     Then,  FIG. 5  shows a flow of a processing executed in the sub-disk control unit  7  until the access information is reported to the original disk control unit  3  since the access to the sub-disk unit  8  was ended. 
     In  FIG. 5A , if a command received at the channel command analyzing section  36  of the sub-disk control unit  7  is an access end command relative to the sub-disk unit  8  which is placed in the duplexed data state (step  300 ), then the end of the access is reported to the positive disk control unit  3  by a dedicated command from the positive disk control unit command issuing section  37  (step  310 ). 
     Then, if the write access of the duplexing interruption is carried out with reference to the state management table  39  (step  320 ), then a processing {circle around ( 2 )} in which the access information is reported to the original disk control unit  3  is realized by a method of  FIG. 5B  or  FIG. 5C . 
     When this processing {circle around ( 2 )} is realized by the method shown in  FIG. 5B , the access information read request from the original disk control unit  3  is awaited (Step  330 ). Then, after such request is received, the access information is reported to the original disk control unit  3  by a dedicated command (step  340 ), and the contents of the access information management table  40  are cleared (step  350 ). 
     on the other hand, when the processing {circle around ( 2 )} is realized by the method shown in  FIG. 5C , the access information is reported to the original disk control unit  3  by a dedicated command (step  360 ), and the contents of the access information management table  40  are cleared (step  370 ). Thereafter, the duplexing interruption information is registered on the state management table  39  (step  380 ). 
       FIG. 6  shows a flow of a processing executed by the original disk control unit  3  until the access information of the sub-disk unit  8  is obtained after the access end report to the sub-disk unit  8  was received. 
     In  FIG. 6A , after the access end report was received at the sub-disk control unit command analyzing section  32  of the original disk control unit  3  (step  400 ), the state management table  33  is checked. If the write access of the duplexing interruption is carried out (step  410 ), then an access information registration processing {circle around ( 3 )} may be realized by either method shown in  FIG. 6B  or  FIG. 6C . 
     If the processing shown in  FIG. 6B  is executed, then the access information read command is issued to the sub-disk control unit  7  by a dedicated command (step  420 ), and the read-out information is merged to the access information relative to the original disk unit  4  and then registered on the access information management table  34  (step  430 ). 
     If the processing shown in  FIG. 6C  is executed, then the report of the access information from the sub-disk control unit  7  is awaited (step  440 ), and the received information is merged to the access information relative to the original disk unit  4  and then registered on the access information management table  34  (step  450 ). Thereafter, the sub-side write access information of the duplexing interruption is registered on the state management table  33  (step  460 ). 
     Further,  FIG. 7  shows a flow of a processing executed in the original disk control unit  3  when the duplexing is resumed from the interruption in the embodiment. 
     A command in which information indicating whether data of the original disk unit  4  obtained after the duplexing is resumed is used as data of the original disk unit  4  obtained in the duplexing interruption (original data is used) or as data of the sub-disk unit  8  (sub-data is used) is added to a conventional duplexing resume command is prepared as a new duplexing resume command. 
     In  FIG. 7A , if it is determined by the channel command analyzing section  30  of the original disk control unit  3  that the command from the original channel unit  2  is the duplexing resume command (step  600 ), then the state management table  33  is checked. Then, if such command is placed in other states than the duplexing interruption state (step  610 ), then the command is rejected (step  620 ). If the state is the duplexing interruption state and the added information of the duplexing resume command represents original data use (step  630 ), then the access information management table  34  is checked, and the write command relative to the access place is issued to the sub-disk unit  8  (step  640 ). If the added information of the duplexing resume command does not represent the original data use (i.e. represent sub-data use) (step  630 ), then the access information management table  34  is checked, a read command relative to the access place is issued to the sub-disk control unit  7  (step  680 ), and the data thus obtained is written in the original disk unit  4  (step  690 ). 
     Following the steps  640  and  690 , as shown in  FIG. 7B , duplexing information is registered on the state management table  33  (step  650 ), and contents of the access information management table  34  are cleared (step  660 ). Also in the sub-disk control unit  7 , after the writing of received data is ended at the step  640 , or when data was reported at the step  680 , duplexing information is registered on the state management table  39 . 
     As described above, the sub-disk control unit  7  memorizes information of update place in response to the access to the backup data. After the access was ended, the original disk control unit  3  reads out such information from the sub-disk control unit  7 . Alternatively, after the access was ended, the sub-disk control unit  7  reports such information to the original disk control unit  3  so that each time the access occurs in the backup data, the update place obtained by the accessing of the sub-disk unit  8  is reported to the original disk control unit  3 . 
     As described above, according to the multiplexed data memory system of the present invention, under the circumstances comprising the original system for executing the business and the sub-system holding its backup data, resources may be effectively utilized by accessing the read and write from and on the backup data. 
     Also, the multiplexing of data may be efficiently reorganized by copying only the update place data from the original system disk unit to the sub-system disk unit or copying only the update place data from the sub-system disk unit to the original system disk unit after the access was ended. 
     Having described a preferred embodiment of the invention with reference to the accompanying drawings, it is to be understood that the invention is not limited to that precise embodiment and that various changes and modifications could be effected therein by one skilled in the art without departing from the spirit or scope of the invention as defined in the appended claims.