Method and apparatus for accessing data in a shadow set after a failed data operation

• US 6,192,460 B1
• Filed: 12/16/1997
• Issued: 02/20/2001
• Est. Priority Date: 12/16/1997
• Status: Expired due to Term

• Current Assignee: Hewlett Packard Enterprise Development LP (Hewlett-Packard Enterprise Company)
• Original Assignee: Compaq Computer Corporation (HP Inc.)
• Inventors: Thiel, David William, Davis, Scott Howard, Goleman, William Lyle
• Primary Examiner(s): Pan, Daniel H.
• Assistant Examiner(s): Nguyen, Dzung C.
• Application Number:
  US08/991,828
• Time in Patent Office: 1,162 Days
• Field of Search: 712/1, 712/32, 712/33, 707/100, 707/201, 707/204
• US Class Current: 712/1
• CPC Class Codes: G06F 11/1471 involving logging of persistent data for recovery
• CPC Class Codes: G06F 11/2064 while ensuring consistency
• CPC Class Codes: G06F 11/2082 Data synchronisation
• CPC Class Codes: G06F 2201/82 Solving problems relating to consistency ensuring consistency in mirrored systems G06F11/2064
• CPC Class Codes: Y10S 707/99952 Coherency, e.g. same view to multiple users
• CPC Class Codes: Y10S 707/99953 Recoverability

Abstract

Disclosed is a method and apparatus for accessing data in a computer system after a failed data operation in which I/O process state information is unknown. The failed data operation may cause data inconsistency among multiple devices associated with a shadow set for storing data. The disclosed system includes techniques for allowing continued data accesses while simultaneously re-establishing data consistency among members of the shadow set.

Claims

1. A method of accessing data in a computer system from a shadow set after a failed data operation, the method comprising the steps of:

detecting said failed data operation in the computer system;

maintaining a host transaction list by recording data operations in said host transaction list indicating that, upon completion of each of said data operations, a storage area of the shadow set associated with each of said data operations contains only consistent data; and

performing another data operation subsequent to the failed data operation and determining directly from an entry in said host transaction list whether a storage area associated with said another data operation contains consistent data, wherein said determining is accomplished without performing a read operation on a member of the shadow set.

2. The method of claim 1 further including the step of:

performing a merge operation to reestablish data consistency for the shadow set, said merge operation producing a merged region including portions of the shadow set containing consistent data; and

wherein said step of performing another data operation uses said merged region to determine if a storage area associated with the other data operation contains consistent data.

3. The method of claim 1, wherein the computer system includes a plurality of host processors, and said step of maintaining a transaction list is performed for each of said plurality of host processors.

4. The method of claim 1 further including the step of:

reinitializing said host transaction list in response to detecting a failed data operation.

5. The method of claim 2, wherein said shadow set includes a plurality of members, and said step of performing another data operation includes the steps of:

determining a type of data operation of the other data operation;

upon determining that the type is a read data operation, performing the steps of;

searching said host transaction list to determine if an entry of said host transaction list is associated with a location which matches a location associated with the read operation; and

upon determining that said host transaction list includes the entry having a matching location, performing the read operation by reading data from any member of the shadow set.

6. The method of claim 5, wherein, upon determining that the type is a read data operation and that said host transaction list does not include an entry having a matching location, the method further includes performing the steps of:

determining if the location associated with the read operation is within said merged region;

upon determining that the location is within said merged region, performing the read operation by reading data from any member of the shadow set;

upon determining that the location is not within said merged region, performing a data consistency technique to ensure that data included in the location is consistent upon completion of the read operation.

7. The method of claim 6, wherein said step of performing a data consistency technique includes performing a read and write technique which includes performing the steps of:

reading data from one member of the shadow set; and

writing out the data to other members of the shadow set.

8. The method of claim 6, wherein said step of performing a data consistency techniques includes performing a read, compare, and write technique which includes performing the steps of:

reading first data from one member of the shadow, set;

determining if the first data for the read operation is consistent with other data by comparing the first data read from one member of the shadow set to the other data stored at other members of the shadow set; and

upon determining that there is a data inconsistency, writing the first data to other members of the shadow set.

9. The method of claim 2, wherein the step of performing a merge operation includes the steps of:

performing a data consistency technique for each portion of storage of the shadow set.

10. The method of claim 9, wherein said step of performing a data consistency technique includes the step of performing a read and write technique, said step of performing said read and write techniques including the steps of:

reading data from one member of the shadow set; and

writing out the data to other members of the shadow set.

11. The method of claim 9, wherein said step of performing a data consistency technique includes the step of performing a read, compare, and write technique, said step of performing said read, compare and write technique including the steps of:

reading first data from one member of the shadow set;

determining if the first data for the read operation is consistent by comparing the first data read from one member of the shadow set to other data stored at other members of the shadow set; and

upon determining that there is a data inconsistency, writing the first data to other members of the shadow set.

12. The method of claim 2 wherein said computer system includes a plurality of host computers, the merge operation is executed in a first of said plurality of host computers, and a second of said plurality of host computers failed to complete the failed data operation.

13. The method of claim 1, wherein said host transaction list is a bit map.