Transferring data between storage media while maintaining host processor access for I/O operations

• US 5,210,865 A
• Filed: 08/04/1992
• Issued: 05/11/1993
• Est. Priority Date: 06/30/1989
• Status: Expired due to Term

• Current Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Original Assignee: Digital Equipment Corporation (HP Inc.)
• Inventors: Thiel, David W., Davis, Scott H., Goleman, William L.
• Primary Examiner(s): Dixon, Joseph L.
• Assistant Examiner(s): Elmore, Reba I.
• Application Number:
  US07/925,307
• Time in Patent Office: 280 Days
• Field of Search: 364/200 MS File, 364/900 MS File, 395/575 MS
• US Class Current: 714/6.1
• CPC Class Codes: G06F 11/16 Error detection or correction of the data by redundancy in hardware
• CPC Class Codes: G06F 11/2082 Data synchronisation
• CPC Class Codes: G06F 11/2087 with a common controller

Abstract

A system and method for transferring data from a first storage medium to a second storage medium, each of the storage media being divided into corresponding data blocks, the method comprising steps of: (a) reading data stored in a first data block in the first storage medium, the first data block initially constituting a current data block; (b) comparing data read in the current data block to data stored in a corresponding data block in the second storage medium; (c) if the data compared in step b are identical, reading data stored in a different data block in the first storage medium, the different data block becoming the current data block, and returning to step b; (d) modifying the data stored in one of the storage media such that the data in the current data block is identical to the corresponding data in the second storage medium; and (e) rereading the data in the current data block and returning to step b.

Claims

1. A method of transferring data between a first storage medium and a second storage medium, at least said first storage medium being accessible to one or more host processors for I/O operations that include writing data to said first storage medium, each of said storage media including data blocks with at least some data blocks of said first storage medium having corresponding data blocks in said second storage medium, said method comprising the steps of:

(a) reading data stored in a first data block in said first storage medium, the first data block initially constituting a current data block;

(b) comparing the data read in said current data block to data stored in a corresponding data block in said second storage medium;

(c) if the data compared in step b are identical, reading data stored in another data block in said first storage medium, said another data block becoming the current data block, and returning to step b;

(d) if the data compared in step b are not identical, modifying the data stored in one of said storage media by transferring data between said storage media to cause the data in said current data block and the data in said corresponding data block in said second storage medium to be identical while maintaining access to said first storage medium for said I/O operations by said one or more of said host processors; and

(e) rereading the data in said current data block and returning to step b.

2. The method of claim 1 wherein said step of modifying comprises modifying the data in said second storage medium.

3. The method of claim 2 wherein said step of modifying comprises writing said data read from the current data block in said first storage medium to the corresponding data block in said second storage medium.

4. The method of claim 1 wherein said different data block is a data block adjacent to said current data block.

5. The method of claim 1 wherein each data block in said first storage medium is compared to a corresponding data block in said second storage medium.

6. The method of claim 1 wherein each of said storage media are members of a shadow set of storage media.

7. The method of claim 6 wherein each of said storage media may be directly accessed by a host processor.

8. The method of claim 6 wherein each of said storage media may be directly accessed by each of a plurality of host processors.

9. The method of claim 1 wherein said storage media are disk storage devices.

12. The method of claim 1 wherein each of said host processors will transmit any write requests to said storage media first to said first storage medium and, after said write request to said first storage medium has completed, will transmit said write request to said second storage medium.

13. The method of claim 1 wherein each of said host processors maintains a table including information that enables said host processor to determine if said data transfers are occurring between said of storage media.

10. A method of managing a shadow set of storage media that are accessible by one or more host processors for I/O operations that include writing data thereto, each one of said storage media having storage locations at least some of which correspond to storage locations of another one of said storage media, the method comprising the steps of:

A. carrying out successive comparisons of data stored in said corresponding locations of said plurality of said storage media, respectively; and

B. performing a management operation on at least one of said storage media, said management operation comprising, for each of said corresponding locations where said comparisons indicated that the data in said corresponding locations were not identical;

a. reading data from locations in a first one of said storage media and writing said data to said corresponding locations a second one of said storage media while maintaining access to at least said first storage medium for said I/O operations by said one or more of said host processors;

b. comparing the data in said corresponding locations after said writing to determine if the data in said corresponding locations are identical; and

c. repeating step a if the comparison of step b indicates that the data in said corresponding locations are not identical, otherwise terminating said management operation as to said storage locations.

14. The method of claim 10 wherein each of said storage media may be directly accessed by each of a plurality of host processors.

15. The method of claim 10 wherein each of said host processors will transmit any write requests to said storage media first to said one of said storage media and, after said write request to said one of said storage media has completed, will transmit said write request to said another of said storage media.

16. The method of claim 10 wherein each of said host processors maintains a table including information that enables said host processor to determine whether said management operation is being performed on one or more of said storage media in said shadow set.

17. The method of claim 10 wherein step B(b) comprises rereading said data from said locations in said one of said storage media and comparing said reread data to data in said corresponding locations in said another of said storage media.

18. The method of claim 10 wherein steps B(a) and B(b) are repeated recursively for the same corresponding locations until the data stored in said corresponding locations is determined to be identical.

11. An apparatus for managing a shadow set of storage media accessible by one or more host processors for I/O operations that include writing data thereto, each one of said storage media having storage locations at least some of which correspond to storage locations of another one of said storage media, comprising:

means for carrying out successive comparisons of data stored in said corresponding locations of said plurality of said storage media, respectively; and

means, responsive to said comparisons, for performing a management operation on at least one of said storage media, said management operation comprising, for each of said corresponding locations where said comparisons indicated that the data in said corresponding locations were not identical;

a. reading data from locations in a first one of said storage media and writing said data to said corresponding locations in a second one of said storage media while maintaining access to at least said first storage medium for said I/O operations by said one or more of said host processors;

b. comparing the data in said corresponding locations after said writing to determine if the data in said corresponding locations are identical; and

c. repeating step a if the comparison of step b indicates that the data in said corresponding locations are not identical, otherwise terminating said management operation as to said storage locations.

19. The apparatus of claim 11 wherein each of said host processors will transmit any write requests to said storage media first to said one of said storage media and, after said write request to said one of said storage media has completed, will transmit said write request to said another of said storage media.

20. The apparatus of claim 11 wherein each of said host processors maintains a table including information that enables said host processor to determine whether said management operation is being performed on one or more of said storage media in said shadow set.

21. The apparatus of claim 11 wherein each of said storage media may be directly accessed by each of a plurality of host processors.

22. The apparatus of claim 11 wherein said management operation comprises rereading said data from said locations in said one of said storage media after said writing and comparing said reread data to data in said corresponding locations in said another of said storage media.

23. The apparatus of claim 11 wherein said means for performing said management operation repeats said reading and comparing recursively for the same corresponding locations until the data stored in said corresponding locations is determined to be identical.