Database backup system ensuring consistency between primary and mirrored backup database copies despite backup interruption

• US 6,199,074 B1
• Filed: 04/05/1999
• Issued: 03/06/2001
• Est. Priority Date: 10/09/1997
• Status: Expired due to Fees

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Slone, Harold Glen, Spear, Gail Andrea, Yudenfriend, Harry Morris, Kern, Robert Frederic, Micka, William Frank, Nick, Jeffrey Mark, Perry, Larry Richard, Petersen, David Bradley
• Primary Examiner(s): Alam, Hosain T.
• Assistant Examiner(s): ALAM, SHAHID AL
• Application Number:
  US09/286,389
• Time in Patent Office: 701 Days
• Field of Search: 707/1, 707/2, 707/10, 707/100, 707/200, 707/201, 707/202, 707/203, 707/204, 707/8, 700/10, 709/222, 709/223, 714/6, 717/3, 379/265
• US Class Current: 1/1
• CPC Class Codes: G06F 11/2058 using more than 2 mirrored copies
• CPC Class Codes: G06F 11/2064 while ensuring consistency
• CPC Class Codes: G06F 11/2069 Management of state, configuration or failover
• CPC Class Codes: G06F 11/2071 using a plurality of controllers
• CPC Class Codes: G06F 11/2082 Data synchronisation
• CPC Class Codes: Y10S 707/99952 Coherency, e.g. same view to multiple users
• CPC Class Codes: Y10S 707/99953 Recoverability
• CPC Class Codes: Y10S 707/99955 Archiving or backup

Abstract

A database management system ensures consistency between primary and mirrored backup copies of a database, despite occurrence of a suspending condition interrupting the normal process of mirroring the primary database. One or more primary controllers are provided, each having a data storage unit with multiple primary data storage devices. Multiple secondary controllers each have multiple associated secondary data storage devices, each secondary controller being coupled to one primary controller. One or more primary databases reside on the primary devices, with a corresponding number of secondary databases residing on the secondary devices. Each secondary database mirrors a corresponding primary database. Either a host, attached to a primary controller, or one of the primary controllers itself, maintains a map cross-referencing each primary and secondary database with the primary and secondary devices containing portions thereof. If a predefined “suspending condition” affecting data mirroring occurs, the host or primary controller consults its map to identify all primary and secondary devices affected by the condition. Then, each primary controller stops all ongoing and future read/writes with each of its affected primary devices. Each primary controller also directs each secondary controller having an affected secondary device to stop mirroring the primary databases stored on that device. Then, the primary controller starts intermediate change recording and resumes read/writes with its primary devices. When the suspending condition ends, each primary controller applies the appropriate logged changes to its secondary database(s) and then reactivates each secondary database.

Claims

1. A method for maintaining backup data in a database management system (DBMS) including at least one primary controller, multiple primary data storage devices each coupled to one of the primary controllers, multiple secondary data storage devices each coupled to one of multiple secondary controllers, each secondary controller being coupled to one of the primary controllers, wherein one or more primary databases reside on the primary data storage devices and a corresponding number of secondary databases reside on the secondary data storage devices, wherein the DBMS updates each secondary database to mirror its corresponding primary database, each corresponding primary and secondary database together constituting a mirrored pair, the method comprising:

at a first time, detecting unavailability of a first database for read/writes, said first database being a member of a first mirrored pair including the first database and a counterpart database;

identifying all primary and secondary data storage devices containing any data of the first mirrored pair of databases, said identified primary and secondary data storage devices constituting affected primary and secondary devices;

discontinuing all read/write operations by the affected primary devices ongoing at the first time, also preventing future read/write by the affected primary devices;

instructing each secondary controller coupled to any affected secondary devices to terminate updating of the affected secondary devices;

detecting termination of updating by the secondary controllers, and in response thereto, resuming read/writes with the affected primary devices;

each primary controller coupled to affected primary devices receiving changes to the primary database of the first mirrored pair, and in response thereto, logging the received changes;

detecting removal of the suspending condition, and in response thereto, resynchronizing the secondary database of the mirrored pair by;

applying the logged changes to the secondary devices containing the secondary database of the mirrored pair; and

instructing the secondary controllers to resume updating of the secondary database of the mirrored pair to mirror its corresponding primary database.

2. The method of claim 1, each primary controller being coupled to at least one host computer.

3. The method of claim 2, the detecting of the first database'"'"'s unavailability for read/writes being performed by one of the host computers experiencing a failed read/write operation.

4. The method of claim 1, the first database being one of the primary databases, and the counterpart database being a corresponding one of the secondary databases.

5. The method of claim 1, the first database being one of the secondary databases, and the counterpart database being a corresponding one of the primary databases.

6. The method of claim 2, the identifying of all primary and secondary data storage devices containing any data of the first mirrored pair of databases comprising:

the host or primary controller accessing a machine-readable map associating primary and secondary data storage devices with databases contained thereon.

7. The method of claim 2, where:

the at least one primary controller is a single primary controller;

the primary controller contains a machine-readable map associating primary and secondary data storage devices with databases contained thereon; and

the identifying of all primary and secondary data storage devices containing any data of the first mirrored pair of databases comprises the primary controller accessing the map.

8. The method of claim 1, the discontinuing of all read/write operations with the affected primary devices ongoing at the first time and preventing of future read/writes with the affected primary devices comprising:

the primary controllers coupled to affected primary devices causing discontinuance of all read/write operations with the affected primary devices ongoing at the first time and prevention of future read/writes with the affected primary devices by issuing a DISABLE READ/WRITES command to its affected devices.

9. The method of claim 1, the at least one primary controller comprising multiple primary controllers.

10. The method of claim 1, the suspending condition comprising one of the primary or secondary data storage units sending a message that it is unavailable for input/output operations.

11. The method of claim 1, the suspending condition comprising an interruption in communications between a primary controller and one or more secondary controllers.

12. The method of claim 1, the suspending condition comprising a cache failure occurring in one of the secondary data storage units.

13. The method of claim 1, the suspending condition comprising one of the primary data storage units.

14. The method of claim 1, the suspending condition comprising removal of electrical power from a secondary controller.

15. The method of claim 2, the detecting of discontinuance of updating of the secondary database being performed by the host, wherein the host issues an ENABLE READ/WRITES command to the primary controller and, in response to the ENABLE READ/WRITES command, the primary controller resumes exchanges of data with the primary data storage devices.

16. The method of claim 1, the logging of changes to the primary database comprising maintenance of a bit map where each bit represents status of a corresponding section of the primary database as being changed or unchanged since the discontinuing of all read/write operations by the affected primary devices.

17. The method of claim 1, the primary data storage units comprising magnetic data storage disks, the sections comprising storage tracks.

18. The method of claim 1, the logging of changes to the primary database comprising logging each change made to the primary database, a time of said change, and an address of said change in the primary database.

19. The method of claim 1, the discontinuance of all read/write operations discontinuing any read or write operation being performed by an affected primary device.

20. The method of claim 1, the first database comprising a primary database, the method further comprising:

applying the logged changes to the primary devices containing the first database.

21. The method of claim 1, the instructing of each secondary controller coupled to any affected secondary devices to terminate updating of the affected secondary devices comprising:

the primary controllers coupled to secondary controllers that are coupled to an affected secondary device sending commands to said secondary controllers to terminate updating of the affected secondary devices.

22. The method of claim 1, the detecting of termination of updating by the secondary controllers comprising:

the primary controllers receiving confirmation signals from the secondary controller coupled to affected secondary devices.

23. A database management system, comprising:

at least one primary controller;

multiple primary data storage devices each coupled to one of the primary controllers;

multiple secondary controllers, each coupled to one of the primary controllers;

multiple secondary data storage devices each coupled to one of the secondary controllers;

multiple primary databases residing on the primary data storage devices and a corresponding number of secondary databases residing on the secondary data storage devices

wherein the primary controllers and secondary controllers are programmed to perform a method for managing the primary and secondary databases, said method comprising;

updating each secondary database to mirror contents of its corresponding primary database;

at a first time, detecting unavailability of a first database for read/writes, said first database being a member of a first mirrored pair including the first database and a counterpart database;

identifying all primary and secondary data storage devices containing any data of the first mirrored pair of databases, said identified primary and secondary data storage devices constituting affected primary and secondary devices;

discontinuing all read/write operations by the affected primary devices ongoing at the first time, also preventing future read/write by the affected primary devices;

instructing each secondary controller coupled to any affected secondary devices to terminate updating of the affected secondary devices;

detecting termination of updating by the secondary controllers, and in response thereto, resuming read/writes with the affected primary devices;

each primary controller coupled to affected primary devices receiving changes to the primary database of the first mirrored pair, and in response thereto, logging the received changes;

detecting removal of the suspending condition, and in response thereto, resynchronizing the secondary database of the mirrored pair by;

applying the logged changes to the secondary devices containing the secondary database of the mirrored pair; and

instructing the secondary controllers to resume updating of the secondary database of the mirrored pair to mirror its corresponding primary database.

24. The system of claim 23, each primary controller being coupled to at least one host computer.

25. The system of claim 24, the detecting of the first database'"'"'s unavailability for read/writes being performed by one of the host computers experiencing a failed read/write operation.

26. The system of claim 23, the first database being one of the primary databases, and the counterpart database being a corresponding one of the secondary databases.

27. The system of claim 23, the first database being one of the secondary databases, and the counterpart database being a corresponding one of the primary databases.

28. The system of claim 24, the identifying of all primary and secondary data storage devices containing any data of the first mirrored pair of databases comprising:

the host accessing a machine-readable map associating primary and secondary data storage devices with databases contained thereon.

29. The system of claim 24, where:

the at least one primary controller is a single primary controller;

the primary controller contains a machine-readable map associating primary and secondary data storage devices with databases contained thereon; and

the identifying of all primary and secondary data storage devices containing any data of the first mirrored pair of databases comprises the primary controller accessing the map.

30. The system of claim 23, the discontinuing of all read/write operations with the affected primary devices ongoing at the first time and preventing of future read/writes with the affected primary devices comprising:

the primary controllers coupled to affected primary devices causing discontinuance of all read/write operations with the affected primary devices ongoing at the first time and prevention of future read/writes with the affected primary devices by issuing a DISABLE READ/WRITES command to its affected devices.

31. The system of claim 23, the at least one primary controller comprising multiple primary controllers.

32. The system of claim 23, the suspending condition comprising one of the primary or secondary data storage units sending a message that it is unavailable for input/output operations.

33. The system of claim 23, the suspending condition comprising an interruption in communications between a primary controller and one or more secondary controllers.

34. The system of claim 23, the suspending condition comprising a cache failure occurring in one of the secondary data storage units.

35. The system of claim 23, the suspending condition comprising one of the primary data storage units.

36. The system of claim 23, the suspending condition comprising removal of electrical power from a secondary controller.

37. The system of claim 24, the detecting of discontinuance of updating of the secondary database being performed by the host, wherein the host issues an ENABLE READ/WRITES command to the primary controller and, in response to the ENABLE READ/WRITES command, the primary controller resumes exchanges of data with the primary data storage devices.

38. The system of claim 23, the logging of changes to the primary database comprising maintenance of a bit map where each bit represents status of a corresponding section of the primary database as being changed or unchanged since discontinuance of all read/write operations by the affected primary devices.

39. The system of claim 23, the primary data storage units comprising magnetic data storage disks, the sections comprising storage tracks.

40. The system of claim 23, the logging of changes to the primary database comprising logging each change made to the primary database, a time of said change, and an address of said change in the primary database.

41. The system of claim 23, the discontinuance of all read/write operations discontinuing any read or write operation being performed by an affected primary device.

42. The system of claim 23, the first database comprising a primary database, the method further comprising:

applying the logged changes to the primary devices containing the first database.

43. The system of claim 23, the instructing of each secondary controller coupled to any affected secondary devices to terminate updating of the affected secondary devices comprising:

the primary controllers coupled to secondary controllers that are coupled to an affected secondary device sending commands to said secondary controllers to terminate updating of the affected secondary devices.

44. The system of claim 23, the detecting of termination of updating by the secondary controllers comprising:

the primary controllers receiving confirmation signals from the secondary controller coupled to affected secondary devices.