Method and system for more efficiently providing a copy in a raid data storage system

• US 6,415,296 B1
• Filed: 03/31/1999
• Issued: 07/02/2002
• Est. Priority Date: 03/31/1999
• Status: Expired due to Term

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Islam, Shah Mohammed Rezaul, Sarkar, Prasenjit, Challener, David Carroll, Krishnamurthy, Vikram Harakere, Richardson, Philip Anthony
• Primary Examiner(s): Shah, Sanjiv
• Assistant Examiner(s): FLEURANTIN, JEAN B
• Application Number:
  US09/282,715
• Time in Patent Office: 1,189 Days
• Field of Search: 707/200-204, 717/11, 711/162
• US Class Current: 1/1
• CPC Class Codes: G06F 3/0613 in relation to throughput
• CPC Class Codes: G06F 3/0617 in relation to availability
• CPC Class Codes: G06F 3/065 Replication mechanisms
• CPC Class Codes: G06F 3/0689 Disk arrays, e.g. RAID, JBOD
• CPC Class Codes: Y10S 707/99953 Recoverability

Abstract

The present invention provides a method and system for more efficiently providing a copy of a portion of a source drive of a plurality of drives in a redundant array of inexpensive disks (RAID) data storage system. The portion of the source drive includes a plurality of segments. The method and system include providing the copy of the plurality of segments from the source drive to the target drive. The plurality of segments can be modified during the step of providing the copy. The method and system further include providing another copy of a portion of the plurality of segments that have been modified since the step of providing the copy commenced if a portion of the plurality of segments have been modified since copying commenced.

Claims

1. A method for copying a portion of a source drive to a target drive, the source drive and the target drive being part of a plurality of drives in a redundant array of inexpensive disks (RAID) data storage system, the portion of the source drive including a plurality of segments, the method comprising the steps of:

(a) providing a copy of the plurality of segments from the source drive to the target drive, wherein the plurality of segments can be modified during the step of providing the copy;

(b) providing another copy of a portion of the plurality of segments that have been modified since being copied if the portion of the plurality of segments have been modified; and

(c) providing a copy of each of a second portion of the plurality of segments for which a current copy had not been provided, if any, while allowing input to and output from the source drive and the target drive.

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

(c) repeating step (b) for a predetermined period of time.

3. The method of claim 1 further comprising the step of:

(c) repeating step (b) until a number of segments in the portion of the plurality of segments that have been modified does not substantially decrease.

4. The method of claim 1 wherein the copying step (a) further includes the steps of:

(a1) copying a segment of the plurality of segments;

(a2) indicating that the segment has been copied; and

(a3) repeating steps (a1) and (a2) for each remaining segment in the plurality of segments.

5. The method of claim 4 wherein the copying step (a) further includes the steps of:

(a4) indicating whether the portion of the plurality of segments have been modified since the step of providing the copy commenced.

6. The method of claim 5 wherein the copy indicating step (a2) further includes the step of:

(a2i) providing a tag associated with each of the plurality of segments, the tag indicating whether a copy of the segment has been provided to the target drive.

7. The method of claim 6 wherein the modification indicating step (a4) further includes the step of:

(a4i) resetting the tag for each of the portion of the plurality of segments to indicate that the portion of the plurality of segments is to be copied again.

8. A method for copying a portion of a source drive to a target drive, the source drive and the target drive being part of a plurality of drives in a redundant array of inexpensive disks (RAID) data storage system, the portion of the source drive including a plurality of segments, the method comprising the steps of:

(a) providing a copy of the plurality of segments from the source drive to the target drive, wherein the plurality of segments can be modified during the step of providing the copy;

(b) providing another copy of a portion of the plurality of segments that have been modified since being copied if the portion of the plurality of segments have been modified; and

(c) providing a copy of each of a second portion of the plurality of segments for which a current copy had not been provided while allowing input to and output from the source drive and the target drive, the step of providing the copy of the second portion of the plurality of segments further including the steps of;

(c1) if modifications are to be made to a segment of the plurality of segments and a copy of the segment has not been provided yet, providing the copy of the segment to the target drive, indicating that the copy of the segment has been provided, and making the modifications to the segment in the source drive;

(c2) if modifications are to be made to a segment and the copy of the segment has already been provided, making the modifications to the segment in the source drive;

(c3) providing the segment from the source drive if the segment is requested for reading and it is indicated that the copy of the segment has not been provided on the target drive;

(c4) providing the segment from the source drive if the segment is requested for reading and modifications have not been made to the segment since the step of providing the copy (c) commenced;

(c5) providing the segment from the source drive if the segment is requested for reading, the modifications have been made to the segment since the step of providing the copy commenced, and the modifications are desired; and

(c6) providing the copy of the segment from the target drive if the segment is requested for reading, modifications have been made to the segment since the step of providing the copy commenced, and the modifications are desired.

9. A system for copying a portion of a source drive to a target drive, the source drive and the target drive being part of a plurality of drives in a redundant array of inexpensive disks (RAID) data storage system, the portion of the source including a plurality of segments, the system comprising:

a copy engine coupled with the source drive and the target drive for providing a copy of the plurality of segments from the source drive to the target drive, for allowing the plurality of segments to be modified during the step of providing the copy, and for providing another copy of a portion of the plurality of segments that have been modified since providing the copy commenced if a portion of the plurality of segments have been modified since copying commenced, wherein the copy engine further provides a copy of a second portion of the plurality of segments for which a current copy has not been provided, if any, while allowing input to and output from the source drive and the target drive; and

metadata coupled with the copy engine including an indication of whether the copy of the plurality of segments has been provided to the target drive and whether a portion of the plurality of segments has been modified since copying commenced.

10. The system of claim 9 wherein the copy engine further repeats providing another copy of a portion of the plurality of segments that have been modified for predetermined period of time.

11. The system of claim 9 wherein the copy engine further repeats providing another copy of a portion of the plurality of segments that have been modified until a number of segments in the portion of the plurality of segments that have been modified does not substantially decrease.

12. The system of claim 9 wherein the copy engine further copies a segment of the plurality of segments, indicates in the metadata that the segment has been copied, and repeats the copying and indicating steps for each remaining segment in the plurality of segments.

13. The system of claim 12 wherein the metadata further includes an indication of whether the portion of the plurality of segments have been modified since the step of providing the copy commenced.

14. The system of claim 13 wherein the metadata further includes a tag associated with each of the plurality of segments, the tag indicating whether a copy of the segment has been provided to the target drive.

15. The system of claim 14 wherein the indication of whether the tag for the portion of the plurality of segments have been modified is reset to indicate that the portion of the plurality of segments is to be copied again.

16. A system for copying a portion of a source drive to a target drive, the source drive and the target drive being part of a plurality of drives in a redundant array of inexpensive disks (RAID) data storage system, the portion of the source including a plurality of segments, the system comprising:

a copy engine coupled with the source drive and the target drive for providing a copy of the plurality of segments from the source drive to the target drive, for allowing the plurality of segments to be modified during the step of providing the copy, and for providing another copy of a portion of the plurality of segments that have been modified since providing the copy commenced if a portion of the plurality of segments have been modified since copying commenced, wherein the copy engine further provides a copy of a second portion of the plurality of segments for which a current copy has not been provided while allowing input to and output from the source drive and the target drive;

metadata coupled with the copy engine including an indication of whether the copy of the plurality of segments has been provided to the target drive and whether a portion of the plurality of segments has been modified since copying commenced; and

a consistency machine coupled with the source drive and the target drive, the consistency machine for intercepting a write request for modifications to be made to a segment of the plurality of segments, in response to the write request, the consistency machine further for providing a copy of the segment on the target drive if the copy has not been provided yet, indicating that the copy of the segment has been provided if the copy has not been providing yet, and making the modifications to the segment in the source drive after the copy has been provided;

the consistency machine further for making the modifications to the segment in the source drive in response to the request if the copy of the segment has been provided; and

the consistency machine further for intercepting a read request for the segment and in response to the read request, providing the segment from the source drive if it is indicated that a copy of the segment has not been provided on the target drive, providing the segment from the source drive if the modifications have not been made to the segment since the step of providing the copy commenced, providing the segment from the source drive if the modifications have been made to the segment since the step of providing the copy commenced and the modifications are desired, and providing the copy of the segment from the target drive if modifications have been made to the segment since the copy was provided and the modifications are not desired.