Array type disk system updating redundant data asynchronously with data access

• US 5,761,402 A
• Filed: 09/27/1994
• Issued: 06/02/1998
• Est. Priority Date: 03/08/1993
• Status: Expired due to Term

• Current Assignee: Hitachi Maxell Limited (Maxell, Ltd.)
• Original Assignee: Hitachi, Ltd.
• Inventors: Yagisawa, Ikuya, Oeda, Takashi, Kaneda, Yasunori, Yoshida, Minoru, Arakawa, Hiroshi, Honda, Kiyoshi, Matsunami, Naoto, Akiyama, Hitoshi
• Primary Examiner(s): Beausoliel, Jr., Robert W.
• Assistant Examiner(s): Elmore, Stephen C.
• Application Number:
  US08/312,791
• Time in Patent Office: 1,344 Days
• Field of Search: 395/182.04, 395/425, 395/439, 395/440, 395/441, 395/445, 395/453, 364/243, 364/243.41, 364/248.1, 364/944.92, 364/964
• US Class Current: 714/6.24
• CPC Class Codes: G06F 11/1076 Parity data used in redundant arrays of independent storages, e.g. in RAID systems
• CPC Class Codes: G06F 2211/1009 Cache, i.e. caches used in RAID system with parity
• CPC Class Codes: G06F 3/0613 in relation to throughput
• CPC Class Codes: G06F 3/0658 Controller construction arrangements
• CPC Class Codes: G06F 3/0689 Disk arrays, e.g. RAID, JBOD

Abstract

In a disk array system, data read out and data written anew are temporarily held as former data in a former data holding portion. When a write operation has occurred, a CPU searches the holding portion for write data, it generates update data from the new and former write data items, and it holds the generated update data in an update data holding portion. In addition, the CPU stores the storage address of redundant data associated with the held update data, as log data in a log data holding portion. Further, the CPU operates asynchronously with the write operation to read out the redundant data of the address of the holding portion, to calculate new redundant data from the read redundant data and the held update data, and to write the new redundant data into the address of the log data. On this occasion, a parity area and a data area are separated so as to heighten read/write processing speeds and a parity generation processing speed.

Claims

1. An array type disk system, comprising:

a plurality of disk units, each of which includes a data area for storing data therein and a parity area for storing redundant data corresponding to the stored data therein, and which are arranged in the form of arrays and are operated in parallel;

a disk control device which controls data accesses to respective disk units;

a host computer system which commands the disk control device to access the respective disk units;

update data generation means for generating update data by performing an exclusive OR operation between data before a write operation and data to be written when the data is to be first written into an address in a pertinent one of said disk units, and for generating new update data by performing an exclusive OR operation among the data before the write operation, the data to be written and the generated update data when the data is to be written into the address in the pertinent disk unit again, wherein the generation of update data utilizes a singular disk units;

update data holding means for holding therein the update data generated by said update data generation means;

log data generation means for generating a parity address as log data in association with the held update data, the parity address being that address of a particular one of said disk units at which redundant data for the data of the data address is stored;

log data holding means, which includes a nonvolatile memory, for holding therein the log data generated by said log data generation means; and

delayed parity generation means, operating asynchronously with the process of writing the data into said pertinent disk unit, for reading the redundant data associated with the update data out of the parity address of the particular disk unit in accordance with the parity address of the log data, for generating new redundant data on the basis of an exclusive OR operation performed on the redundant data read out of said particular disk unit in accordance with the parity address of the log data and the update data associated therewith from said update data holding means, and for writing the new redundant data into said particular disk unit in accordance with the parity address of the log data, wherein the generation of new redundant data utilizes a singular disk unit.

2. An array type disk system as defined in claim 1, further comprising:

former data holding means for holding therein the data stored in the data areas of the plurality of disk units accessed in the past, as former data in association with access addresses of the stored data;

wherein said update data generation means determines if the data before the write operation is held as the former data in said former data holding means, on the basis of the access address of former data and the address into which the data is to be written, and performing the exclusive OR operation with the held former data as the data before the write operation, subject to the decision that the data before the write operation is held.

3. An array type disk system as defined in claim 2, wherein said former data holding means is a disk cache of an operating system of said host computer system.

4. An array type disk system as defined in claim 2, wherein said former data holding means is provided in a part that is selected from the group consisting of said host computer system and said disk control device.

5. An array type disk system as defined in claim 2, wherein said host computer system includes a main memory, and said former data holding means is provided in said main memory.

6. An array type disk system as defined in claim 1, further comprising:

former parity holding means for holding therein parity addresses accessed before,

wherein during the delayed parity generation process, the operation of reading out the parity address of said particular disk unit is omitted in accordance with the former parity address being held in said former parity holding means.

7. An array type disk system as defined in claim 1, wherein each of said disk units includes at least one data area and at least one parity area, and a separate parity placement system is adopted in which at least one of the areas of said array type disk system has a size not smaller than:

space="preserve" listing-type="equation">S×

n×

(n-1), and

at least one of the parity areas of said array type disk system has a size not smaller than;

space="preserve" listing-type="equation">s×

n,

wherein "s" denotes a length of a data distribution unit (stripe unit) of said array type disk system and "n" denotes a number of disk units included in one parity group.

8. An array type disk system as defined in claim 7, wherein said plurality of disk units are a plurality of sets of arrayed disk units based on a separate parity placement system, and the parity areas of the plurality of sets of arrayed disk units are respectively substituted by those of the other sets.

9. An array type disk system as defined in claim 1, wherein said delayed parity generation means reads a plurality of redundant data items out of particular ones of said disk units collectively in accordance with the parity address of the log data, the redundant data items being respectively associated with a plurality of update data items and the corresponding parity addresses of which lie in a predetermined close range;

generates a plurality of new redundant data items which are results of exclusive OR processings between the redundant data redundant data items into the particular disk units in accordance with the parity address of the log data.

10. An array type disk system as defined in claim 9, wherein one array comprises a plurality of access units includes in each of said plurality of disk units are, and the predetermined close range is a close range which is defined within a predetermined number of access units lying in the identical array.

11. An array type disk system as defined in claim 1, wherein said update data holding means is provided in a part that is selected from the group consisting of said host computer system, and disk control device and said disk units.

12. An array type disk system as defined in claim 1, wherein said log data holding means is provided in a part that is selected from the group consisting of said host computer system, said disk control device not said disk units.

13. An array type disk system as defined in claim 1, wherein said update data generation means is provided in said host computer system.

14. An array type disk system as defined in claim 1, wherein said delayed parity generation means is provided in said host computer system.

15. An array type disk system as defined in claim 1, wherein said update data generation means and said delayed parity generation means are provided in said host computer system.

16. An array type disk system as defined in claim 1, wherein said host computer system includes a main memory, and said update data holding means is provided in said main memory.

17. An array type disk system as defined in claim 1, wherein said host computer system includes a main memory, and said log data holding means is provided in said main memory.

18. An array type disk system as defined in claim 1, wherein:

said host computer system includes said update data generation means and said delayed parity generation means;

each of said disk units includes a disk interface which accepts access control from said disk control device; and

said disk control device is constructed of an array board, including;

a bus interface which is connected to said host computer system, as well as disk interfaces which are respectively provided for said plurality of disk units, and

an MPU (Micro Processsing Unit) which receives the commands from said host computer system through said bus interface and which performs the controls of the access to said plurality of disk units through said disk interfaces in compliance with the commands.

19. An array type disk system as defined in claim 18, wherein said bus interface is directly connected to an internal bus of said host computer system.

20. An array type disk system, comprising:

a plurality of disk units, each of which includes a data area for storing data therein and a parity area for storing redundant data corresponding to the stored data therein, and which are arranged in the form of arrays and are operation in parallel;

a disk control device which controls data accesses to the respective disk units;

a host computer system which commands the disk control device to access the respective disk units;

update data generation means for generating update data by performing an exclusive Or operation between data before a write operation and data to be written when the data is to be first written into an address in a pertinent one of said disk units and for generating new update data by performing an exclusive OR operation among the data before the write operation, the data to be written and the generated update data when the data is to be written into the address in the pertinent disk unit again, wherein the generation of update data utilizes a singular disk unit;

update data holding means for holding therein the update data generated by said update data generation means;

former data holding means for holding read data therein when the data has been read out of a certain data address in a pertinent one of said disk units.

wherein during an operation of writing the data into the data address in the pertinent disk unit, an operation of reading the data out of the data address of said pertinent disk unit is omitted in accordance with the data before the write operation being held in said former data holding means;

log data generation means for generating a parity address as log data, the parity address being that address of a particular one of said disk units at which redundant data for the data of the disk address is stored;

log data holding means, which includes a nonvolatile memory, for holding therein the log data generated by said log data generation means; and

delayed parity generation means, operating asynchronously with the process of writing the data into said pertinent disk unit, for reading the redundant data corresponding to the data address out of the parity address of the particular disk unit in accordance with the parity address of the log data, for generating new redundant data in accordance with an exclusive OR operation performed on the redundant data read out of said particular disk unit in accordance with the parity address of the log data and the update data associated therewith from said update data holding means, and for writing the new redundant data into said particular disk unit in accordance with the parity address of the log data, wherein the generation of new redundant data utilizes a singular disk unit.

21. An array type disk system as defined in claim 20, further comprising:

former parity holding means for holding therein parity addresses accessed before,

wherein during the delayed parity generation process, the operation of reading out the parity address of said particular disk unit is omitted in accordance with the former parity address being held in said former parity holding means.

22. An array type disk system as defined in claim 20, wherein said former data holding means is a disk cache of an operating system of said host computer system.

23. An array disk system as defined in claim 20, wherein each of said disk units includes at least one data area and at least one parity area, and a separate parity placement system is adopted in which at least one of the data areas of said array type disk system has a size not smaller than:

space="preserve" listing-type="equation">s×

n×

(n-1), and

at least one of the parity area of said array type disk system has a size not smaller than;

space="preserve" listing-type="equation">s×

n,

wherein "s" denotes a length of a data distribution unit (stripe unit) of said array type disk system and "n" denotes a number of disk units included in one parity group.

24. An array type disk system as defined in claim 23, wherein said plurality of disk units are a plurality of sets of arrayed disk units based on a separate parity placement system, and the parity areas of the plurality of sets of arrayed disk units are respectively substituted by those of the other sets.

25. An array type disk system as defined in claim 20, wherein said delayed parity generation means read a plurality of redundant data items out of particular ones of said disk units collectively in accordance with the parity address of the log data, the redundant data items being respectively associated with a plurality of update data items and the corresponding parity addresses of which lie in a predetermined close range;

generates a plurality of new redundant data items which are results of exclusive OR processing between the redundant data items and the update data items; and

writes the new redundant data items into the particular disk units in accordance with the parity address of the log data.

26. An array type disk system as defined in claim 25, wherein one array comprises a plurality of access units included in each of said plurality of disk units, and the predetermined close range is a close range which is defined within a predetermined number of access units lying in the identical array.

27. An array type disk system as defined in claim 20, wherein said update data holding means is provided in a part that is selected from the group consisting of said host computer system, said disk control device and said disk units.

28. An array type disk system as defined in claim 20, wherein said log data holding means is provided in a part that is selected from the group consisting of said host computer system, said disk control device and said disk units.

29. An array type disk system as defined in claim 20, wherein said former data holding means is provided in a part that is selected from the group consisting of said host computer system and said disk control device.

30. An array type disk system as defined in claim 20, wherein said update data generation means is provided in said host computer system.

31. An array type disk system as defined in claim 20, wherein said delayed parity generation means is provided in said host computer system.

32. An array type disk system is defined in claim 20, wherein said update data generation means and said delayed parity generation means are provided in said host computer system.

33. An array type disk system as defined in claim 20, wherein said host computer system includes a main memory, and said update data holding means is provided in said main memory.

34. An array type disk system as defined in claim 20, wherein said host computer system includes a main memory, and said former data holding means is provided in said main memory.

35. An array type disk system as defined in claim 20, wherein said host computer system includes a main memory, and said log data holding means is provided in said main memory.

36. An array type disk system as defined in claim 20, wherein:

said host computer system includes said update data generation means and said delayed parity generation means;

each of said disk units includes a disk interface which accepts access control from said disk control device; and

said disk control device is constructed of an array board, including;

a bus interface which is connected to said host computer system, as well as disk interfaces which are respectively provided for said plurality of disk units and

an MPU (Micro Processing Unit) which receives the commands from said host computer system through said bus interface and which performs the controls of the accesses to said plurality of disk units through said disk interfaces in compliance with the commands.

37. An array type disk system as defined in claim 36, wherein said bus interface is directly connected to an internal bus of said host computer system.

38. A method of controlling an array type disk system having:

a plurality of disk units, each of which includes a data area for storing data therein and a parity area for storing redundant data corresponding to the stored data therein, and which are arranged in the form of arrays and are operated in parallel;

a disk control device which controls data accesses to respective disk units;

a host computer system which commands the disk control device to access the respective disk units;

said control method comprising the steps of;

generating update data through calculation of exclusive OR between data before a write operation and data to be written when the data is to be first written into an address in a pertinent one of said disk units, and generating new update data through calculation of exclusive OR among the data before the write operation, the data to be written and the generated update data when the data is to be written into the address in the pertinent disk unit again, wherein the generation of update data utilizes a singular disk unit;

holding the generated update data;

holding a parity address as log data in association with the held update data, the parity address being that address of a particular one of said disk units at which redundant data for the data of the data address is stored; and

reading the redundant data associated with the update data out of the parity address of the particular disk unit in accordance with the parity address of the log data, generating new redundant data which is the result of exclusive OR between the redundant data read out and the update data associated therewith, and writing the new redundant data into said particular disk unit in accordance with the parity address of the log data, asynchronous with the process of writing the data into said pertinent disk unit, wherein the generation of new redundant data utilizes a singular disk unit.