Method and apparatus for identifying changes to a logical object based on changes to the logical object at physical level

• US 6,385,626 B1
• Filed: 11/19/1998
• Issued: 05/07/2002
• Est. Priority Date: 11/19/1998
• Status: Expired due to Term

• Current Assignee: Emc IP Holding Company LLC (Dell Technologies Inc.)
• Original Assignee: EMC Corporation (Dell Technologies Inc.)
• Inventors: Lee, Terry Seto, Tamer, Philip E.
• Primary Examiner(s): Breene, John
• Assistant Examiner(s): PHAM, KHANH B
• Application Number:
  US09/196,651
• Time in Patent Office: 1,265 Days
• Field of Search: 714/20, 711/100, 711/161, 711/162, 711/202, 711/203, 711/204, 707/104, 707/10, 707/103
• US Class Current: 1/1
• CPC Class Codes: G06F 11/1451 by selection of backup contents
• CPC Class Codes: Y10S 707/99953 Recoverability
• CPC Class Codes: Y10S 707/99954 Version management

Abstract

A method and apparatus for indenting changes to a logical object on a host computer by examining information relating to a physical level in a data storage system wherein the logical object is stored. In one embodiment, a method for determining changes to a logical object subsequent to a reference time is described for a logical object that belongs to an application layer of a host computer in a computer system. The computer system includes the host computer, a storage system, and at least one mapping layer that maps the logical object to a physical layer relating to physical storage locations on the storage system. The physical layer includes physical change information relating to changes made to the physical storage locations on the storage system subsequent to the reference time. The method includes steps of mapping the logical object from the application layer to the physical layer to identify which physical storage locations include data corresponding to the logical object, examining the physical change information to identify any of the physical storage locations identified in the step of mapping that include data that has changed subsequent to the reference time, and determining that changes have been made to the logical object when any physical storage locations are identified in the step of examining as including data that has changed subsequent to the reference time.

Claims

1. A method of determining changes to a logical object subsequent to a reference time, the logical object belonging to an application layer of a host computer in a computer system including the host computer, a storage system and at least one mapping layer that maps the logical object to a physical layer relating to physical storage locations on the storage system, the physical layer including physical change information relating to changes made to the physical storage locations on the storage system subsequent to the reference time, the method comprising steps of:

(A) mapping the logical object from the application layer to the physical layer to identify which physical storage locations include data corresponding to the logical object;

(B) examining the physical change information to identify any of the physical storage locations identified in the step (A) that include data that has changed subsequent to the reference time; and

(C) determining that changes have been made to the logical object when any physical storage locations are identified in the step (B) as including data that has changed subsequent to the reference time.

2. The method of claim 1, wherein the logical object includes a plurality of logical units that collectively form the logical object, and wherein the method further comprises a step of:

(D) mapping the physical storage locations identified in the step (B) to the application layer to determine which of the plurality of logical units correspond thereto, thereby identifying which of the plurality of logical units in the logical object include data that has changed subsequent to the reference time.

3. The method of claim 1, wherein the logical object includes a plurality of logical units that collectively form the logical object, and wherein the method fiuther comprises steps of:

(D) making a copy of the logical object at the reference time;

(E) mapping the physical storage locations identified in the step (B) to the application layer to determine which of the plurality of logical units of the logical object correspond thereto, thereby identifying which of the plurality of logical units in the logical object include data that has changed subsequent to the reference time; and

(F) comparing the logical units in the logical object that include data that has changed to the corresponding logical units in the copy of the logical object to determine a nature of the changes to the logical object.

4. The method of claim 3, wherein the logical units in the logical object that include data that has changed each includes several fields of information relevant to an application to which the logical object belongs in the application layer, and wherein the step (F) includes a step of comparing the logical units in the logical object that include data that has changed to the corresponding logical units in the copy of the logical object to determine which of the several fields of information in the logical units that form the logical object have changed subsequent to the reference time.

5. The method of claim 1, wherein the storage system includes an additional mapping layer that maps from the physical layer to a plurality of storage devices included in the storage system, wherein the physical change information is provided at the physical layer, and wherein the step (A) includes a step of mapping the logical object from the application layer only to the physical layer, without further mapping through the additional mapping layer to the plurality of storage devices.

6. The method of claim 1, further comprising a step of:

(D) resetting the physical change information at the reference time.

7. The method of claim 6, wherein the step (D) includes steps of:

(E) mapping the logical object from the application layer to the physical layer to identify which physical storage locations include data corresponding to the logical object; and

(F) resetting the physical change information corresponding to the physical storage locations identified in the step (E).

8. The method of claim 1, wherein the physical storage locations are organized in physical units of information, wherein the physical change information includes at least one bit map with a bit corresponding to each physical unit of information, and wherein the step (B) includes a step of examining the at least one bit map to identify the physical units of information that include data that has changed subsequent to the reference time.

9. The method of claim 1, wherein the physical storage locations are organized in logical volumes that each includes a plurality of tracks, wherein the physical change information includes a bit map for each logical volume, each bit map including a bit corresponding to each track within the corresponding logical volume, and wherein the step (B) includes a step of examining the bit map for at least one of the logical volumes to identify any of the tracks of the at least one of the logical volumes that include data that has changed subsequent to the reference time.

10. The method of claim 1, wherein the logical object includes a plurality of logical units that collectively form the logical object, and wherein the step (A) includes a step of identifying the physical storage locations that include data corresponding to the logical object as a collection of one or more strings of contiguous physical locations, the strings being ordered to maintain a correspondence between the strings and the plurality of logical units to which the strings correspond.

11. A computer readable medium encoded with a computer program for execution on a host computer that is coupled to a storage system and includes at least one mapping layer that maps logical objects belonging to an application layer on the host computer to a physical layer relating to physical storage locations on the storage system, the physical layer including physical change information relating to changes made to the physical storage locations on the storage system subsequent to a reference time, the computer program, when executed on the host computer, performing a method of determining changes to a logical object subsequent to the reference time, the method comprising steps of:

(A) mapping the logical object from the application layer to the physical layer to identify which physical storage locations include data corresponding to the logical object;

(B) examining the physical change information to identify any of the physical storage locations identified in the step (A) that include data that has changed subsequent to the reference time; and

(C) determining that changes have been made to the logical object when any physical storage locations are identified in the step (B) as including data that has changed subsequent to the reference time.

12. The computer readable medium of claim 11, wherein the logical object includes a plurality of logical units that collectively form the logical object, and wherein the method further comprises a step of:

(D) mapping the physical storage locations identified in the step (B) to the application layer to determine which of the plurality of logical units correspond thereto, thereby identifying which of the plurality of logical units in the logical object include data that has changed subsequent to the reference time.

13. The computer readable medium of claim 11, wherein the logical object includes a plurality of logical units that collectively form the logical object, and wherein the method further comprises steps of:

(D) making a copy of the logical object at the reference time;

(E) mapping the physical storage locations identified in the step (B) to the application layer to determine which of the plurality of logical units of the logical object correspond thereto, thereby identifying which of the plurality of logical units in the logical object include data that has changed subsequent to the reference time; and

(F) comparing the logical units in the logical object that include data that has changed to the corresponding logical units in the copy of the logical object to determine a nature of the changes to the logical object.

14. The computer readable medium of claim 13, wherein the logical units in the logical object that include data that has changed each includes several fields of information relevant to an application to which the logical object belongs in the application layer, and wherein the step (F) includes a step of comparing the logical units in the logical object that include data that has changed to the corresponding logical units in the copy of the logical object to determine which of the several fields of information in the logical units that form the logical object have changed subsequent to the reference time.

15. The computer readable medium of claim 11, wherein the storage system includes an additional mapping layer that maps from the physical layer to a plurality of storage devices included in the storage system, wherein the physical change information is provided at the physical layer, and wherein the step (A) includes a step of mapping the logical object from the application layer only to the physical layer, without further mapping through the additional mapping layer to the plurality of storage devices.

16. The computer readable medium of claim 11, wherein the method further comprises a step of:

(D) resetting the physical change information at the reference time.

17. The computer readable medium of claim 16, wherein the step (D) includes steps of:

(E) mapping the logical object from the application layer to the physical layer to identify which physical storage locations include data corresponding to the logical object; and

(F) resetting the physical change information corresponding to the physical storage locations identified in the step (E).

18. The computer readable medium of claim 11, wherein the physical storage locations are organized in physical units of information, wherein the physical change information includes at least one bit map with a bit corresponding to each physical unit of information, and wherein the step (B) includes a step of examining the at least one bit map to identify the physical units of information that include data that has changed subsequent to the reference time.

19. The computer readable medium of claim 11, wherein the physical storage locations are organized in logical volumes that each includes a plurality of tracks, wherein the physical change information includes a bit map for each logical volume, each bit map including a bit corresponding to each track within the corresponding logical volume, and wherein the step (B) includes a step of examining the bit map for at least one of the logical volumes to identify any of the tracks of the at least one of the logical volumes that include data that has changed subsequent to the reference time.

20. The computer readable medium of claim 11, wherein the logical object includes a plurality of logical units that collectively form the logical object, and wherein the step (A) includes a step of identifying the physical storage locations that include data corresponding to the logical object as a collection of one or more strings of contiguous physical locations, the strings being ordered to maintain a correspondence between the strings and the plurality of logical units to which the strings correspond.

21. A host computer for use with a storage system having a plurality of physical storage locations, the host computer comprising:

at least one mapping layer that maps a logical object belonging to an application layer on the host computer to a physical layer relating to the plurality of physical storage locations on the storage system, the physical layer including physical change information relating to changes made to the plurality of physical storage locations on the storage system subsequent to a reference time;

determining means for determining, from the at least one mapping layer, a mapping the logical object from the application layer to the physical layer to identify which of the plurality of physical storage locations include data corresponding to the logical object; and

means for identifying whether changes have been made to the logical object subsequent to the reference time by examining the physical change information corresponding to the plurality of physical storage locations identified by the determining means.

22. The host computer of claim 21, wherein the means for identifying includes:

means for determining that changes have been made to the logical object when any of the plurality of physical storage locations identified by the determining means include data that has changed subsequent to the reference time.

23. The host computer of claim 21, wherein the means for identifying includes:

means for determining that changes have not been made to the logical object when none of the plurality of physical storage locations identified by the determining means includes data that has changed subsequent to the reference time.

24. The host computer of claim 21, wherein the logical object includes a plurality of logical units that collectively form the logical object, and wherein the means for identifying includes:

means for mapping the physical change information corresponding to the plurality of physical storage locations identified by the determining means to the application layer to identify whether the plurality of logical units forming the logical object have changed subsequent to the reference time.

25. The host computer of claim 21, wherein the logical object includes a plurality of logical units that collectively form the logical object, and wherein the host computer further comprises:

means for copying the logical object at the reference time;

means for mapping the physical change information corresponding to the plurality of physical storage locations identified by the determining means to the application layer to identify whether the plurality of logical units forming the logical object have changed subsequent to the reference time; and

means for comparing the logical units in the logical object that include data that has changed to the corresponding logical units in the copy of the logical object to determine a nature of the changes to the logical object.

26. The host computer of claim 25, wherein the logical units in the logical object that include data that has changed each includes several fields of information relevant to an application to which the logical object belongs in the application layer, and wherein the means for comparing compares the logical units in the logical object that include data that has changed to the corresponding logical units in the copy of the logical object to determine which of the several fields of information in the logical units that form the logical object have changed subsequent to the reference time.

27. The host computer of claim 21, wherein the storage system includes an additional mapping layer that maps from the physical layer to a plurality of storage devices included in the storage system, wherein the physical change information is provided at the physical layer, and wherein the determining means determines the mapping of the logical object from the application layer only to the physical layer, without a further mapping through the additional mapping layer o the plurality of storage devices.

28. The host computer of claim 21, further comprising:

means for resetting the physical change information at the reference time.

29. The host computer of claim 28, wherein the means for resetting includes:

means for resetting the physical change information corresponding to the physical storage locations identified by the determining means at the reference time.

30. The host computer of claim 21, wherein the physical storage locations are organized in physical units of information, wherein the physical change information includes at least one bit map with a bit corresponding to each physical unit of information, and wherein the means for identifying examines the at least one bit map to identify whether the physical units of information that include data that has changed subsequent to the reference time.

31. The host computer of claim 21, wherein the physical storage locations are organized in logical volumes that each includes a plurality of tracks, wherein the physical change information includes a bit map for each logical volume, each bit map including a bit corresponding to each track within the corresponding logical volume, and wherein the means for identifying examines the bit map for at least one of the logical volumes to identify whether any of the tracks of the at least one of the logical volumes include data that has changed subsequent to the reference time.

32. The host computer of claim 21, wherein the logical object includes a plurality of logical units that collectively form the logical object, and wherein the determining means determines a mapping of the plurality of logical units to the physical layer to identify the physical storage locations that include data corresponding to the logical object as a collection of one or more strings of contiguous physical locations, the strings being ordered to maintain a correspondence between the strings and the plurality of logical units to which the strings correspond.

33. A storage system for use with a host computer having at least one mapping layer hat maps a logical object belonging to an application layer on the host computer to a physical layer that includes at least one storage volume, the storage system comprising:

at least one storage device that stores data included in the at least one storage volume;

a memory to store change information relating to the at least one storage volume on the storage system, the change information identifying whether changes have been made to the at least one storage volume subsequent to a reference time;

means for receiving, from the host computer, a mapping of the logical object from the application layer to the at least one storage volume that includes data corresponding to the logical object; and

means for determining whether changes have been made to the logical object subsequent to the reference time by examining the change information relating to the at least one storage volume that includes data corresponding to the logical object.

34. The storage system of claim 33, wherein the means for determining includes:

means for identifying that changes have been made to the logical object when any of the data corresponding to the logical object includes data that has changed subsequent to the reference time.

35. The storage system of claim 33, wherein the means for determining includes:

means for identifying that changes have not been made to the logical object when none of the data corresponding to the logical object includes data that has changed subsequent to the reference time.

36. The storage system of claim 33, wherein the memory stores the change information in terms of units of information included in the at least one storage volume.

37. The storage system of claim 36, wherein the change information includes at least one bit map with a bit corresponding to each unit of information included in the at least one storage volume, and wherein the means for determining examines the at least one bit map to identify whether the units of information include data that has changed subsequent to the reference time.

38. The storage system of claim 33, wherein the storage system further comprises:

means for resetting the change information at the reference time.

39. The storage system of claim 38, wherein the memory stores the change information in terms of units of information stored in the at least one storage device, and wherein the means for resetting includes:

means for resetting the change information corresponding to the units of information that include the data corresponding to the logical object.

40. The data storage system of claim 33, wherein the at least one storage volume includes a logical volume that is perceived by the host computer as comprising a physical storage device in the data storage system, and wherein the storage system further comprises:

an additional mapping layer that maps the at least one storage volume to the at least one storage device.

41. The data storage system of claim 33, further comprising:

means for providing the host computer with an indication of whether changes have been made to the logical object subject to the reference time.

42. The data storage system of claim 41, wherein the logical object includes a plurality of logical units that collectively form the logical object, and wherein the means for providing provides an indication to the host computer of whether changes have been made to each of the plurality of logical units that collectively form the logical object.

43. The data storage system of claim 42, wherein the means for receiving receives a mapping of the logical units from the host computer in an order, and wherein the means for providing provides an indication to the host computer, in the order, of whether changes have been made to each of the plurality of logical units that collectively form the logical object.