METHODS AND INFRASTRUCTURE FOR PERFORMING REPETITIVE DATA PROTECTION AND A CORRESPONDING RESTORE OF DATA

• US 20070260645A1
• Filed: 04/27/2007
• Published: 11/08/2007
• Est. Priority Date: 04/28/2006
• Status: Active Grant

• Current Assignee: International Business Machines Corporation, ServiceNow Incorporated
• Original Assignee: International Business Machines Corporation
• Inventors: Prause, Thomas, Augenstein, Oliver
• Granted Patent: US 8,572,040 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G06F 11/1469 Backup restoration techniques
• CPC Class Codes: G06F 11/1471 involving logging of persistent data for recovery
• CPC Class Codes: G06F 11/2094 Redundant storage or storage space G06F11/2056 takes precedence

Abstract

The present invention provides methods and an infrastructure for performing repetitive data protection and a corresponding restore of data for block oriented data objects comprising several indexed segments. For implementing the invention, timestamps t_k are set by a timer k. Only the first data modification of a segment is recorded, after a timestamp t_k has been set, by storing the old data contents of said segment together with the segment index j and said timestamp t_k as undo-log block in a first journal j₀, before overwriting said segment with the modified new data. Besides, said undo-log blocks are transmitted to N journals j_i for storing redundant undo-log information, with N>1 and i=0, . . . , N−1. According to the present invention for each journal j_i journal-specific timestamps t_k/i are generated, so that each journal j_i is written for a different set of timestamps t_k/i.

Claims

1. A method for performing repetitive data protection for data stored in a block oriented data object comprising several indexed segments, the method comprising:

setting timestamps t_k by a timer k;

recording only the first data modification of a segment, after a timestamp t_k has been set, by storing the old data contents of said segment together with the segment index j and said timestamp t_k as undo-log block in a first journal j₀ before overwriting said segment with the modified new data; and

transmitting said undo-log blocks to N journals j_i by storing redundant undo-log information, with N>

1 and i=1, . . . , N−

1;

said method being characterized in that for each journal j_i journal-specific timestamps t_k/i are generated, so that each journal j_i is written for a different set of timestamps t_k/i.

2. The method of claim 1, wherein each set of timestamps t_k/i represents a different time graining and wherein the density of timestamps t_k/i decreases with increasing i.

3. The method of claim 1, wherein the timer k is incremented on request.

4. The method of claim 1, wherein said journal-specific timestamps t_k/i are generated based on the timestamp values t_k set by said timer k.

8. The method of claim 1, characterized in that an offset-table is updated regularly for each timestamp t_k/i, wherein said offset-table comprises for each timestamp t_k/i the offset-position for writing to corresponding journal j_i after said timestamp t_k/i.

9. The method of claim 1, wherein said journals j_i are stored on sequential storage media.

5. The method of claim 5, wherein said journal-specific timestamps t_k/i are defined as the 2ⁱ-th timestamps t_k.

6. The method of claim 5, wherein said journal-specific timestamps t_k/i is incremented only if the ratio of the amount of data written to journal j_i with timestamp t_k/i over the total number of modifications including those undo-log blocks not written to journal j_i during that period gets lower than a predefined ratio for journal j_i.

7. The method of claim 5, wherein said journal-specific timestamps t_k/i for journal j_i (i>

0) is incremented if a recovery point in journal j<sub>i−

1</sub> was set and the ratio of the amount of data written to journal j<sub>i−

1</sub> since last recovery point in journal j_i over the amount of data written to journal j_i since last recovery point in journal j_i exceeds a predefined ratio.

10. A method for restoring data of a block oriented data object comprising several indexed segments by using undo-log information generated and stored as described by:

setting timestamps t_k by a timer k;

recording only the first data modification of a segment, after a timestamp t_k has been set, by storing the old data contents of said segment together with the segment index j and said timestamp t_k as undo-log block in a first journal j₀ before overwriting said segment with the modified new data; and

transmitting said undo-log blocks to N journals j_i by storing redundant undo-log information, with N>

1 and i=1, . . . , N−

1;

said method being characterized in that for each journal j_i journal-specific timestamps t_k/i are generated, so that each journal j_i is written for a different set of timestamps t_k/I, wherein

the data contents of said segments is restored as it was before a given timestamp t; and

each journal j_i represents a different time graining of undo-log information and wherein the density of the corresponding timestamps t_k/i decreases with increasing i;

restoring data comprising;

reading the last journal j<sub>N−

1</sub> starting from the first undo-log block comprising the first timestamp t<sub>k/N−

1</sub> which is the same as or occurs after the time for journal N−

1 which corresponds to timestamp t, till the end of journal j<sub>N−

1</sub>,

reading the next journal j_i in decreasing order starting from the first undo-log block, comprising the first timestamp t_k/i which is the same as or occurs after the time for journal i which corresponds to timestamp t, till the undo-log block comprising the first timestamp t_k/i which is the same as or occurs after the first timestamp for journal i which corresponds to the timestamp t_k/i+1 of journal i+1 having been read of the preceding journal j_i+1;

repeating the preceding step of reading for all next journals j<sub>i−

1</sub>;

and in that

the data stored in an undo-log block read from a journal is only written to the corresponding segment of the data object, if said segment has not been re-written before, initiated by an undo-log block read before from the same journal.

11. The method of claim 10, wherein a restore table is generated for each currently read journal and listing the indexes j of those segments which have already been re-written with said journal.

12. The method of claim 10, wherein in case of an error when reading journal j_N−

1, journal j_N−

2 is read starting from the first undo-log block comprising the first timestamp t<sub>k/N−

2</sub> which is the same as or occurs after timestamp t, until the end of journal j<sub>N−

2</sub>, and wherein the preceding step of reading is repeated for all next journals j<sub>i−

1</sub> according to claim 10.

13. The method of claim 10, wherein in case of an error when reading journal j_i with N−

1>

i>

0, the next journal j<sub>i−

1</sub> in decreasing order is read starting from the first undo-log block, comprising the first timestamp t<sub>k/i−

1</sub> which is the same as or occurs after timestamp t, till the undo-log block comprising the first timestamp t<sub>k/i−

1</sub> which is the same as or occurs after the first timestamp t_k/i+1 having been read of the preceding journal j_i+1 and wherein the preceding step of reading is repeated for all next journals j<sub>i−

1</sub> according to claim 10.

14. The method of claim 10, wherein the offset-positions of the undo-log blocks to be read first in each journal j_i, are identified by means of an offset-table comprising for each timestamp t_k/i the offset-position for writing to the corresponding journal j_i after said timestamp t_k/i.

22. The infrastructure of claim 19, wherein the infrastructure is further capable of carrying out the steps of the method of claim 10.

15. A method for restoring data of a block oriented data object comprising several indexed segments by using undo-log information generated and stored as described by:

setting timestamps t_k by a timer k;

recording only the first data modification of a segment, after a timestamp t_k has been set, by storing the old data contents of said segment together with the segment index j and said timestamp t_k as undo-log block in a first journal j₀ before overwriting said segment with the modified new data; and

transmitting said undo-log blocks to N journals j_i by storing redundant undo-log information, with N>

1 and i=1, . . . , N−

1;

said method being characterized in that for each journal j_i journal-specific timestamps t_k/i are generated, so that each journal j_i is written for a different set of timestamps t_k/i,

wherein

the data contents of said segments is restored as it was before a given timestamp t; and

each journal j_i represents a different time graining of undo-log information, wherein the density of the corresponding timestamps t_k/i decreases with increasing i;

restoring data comprising;

reading the first journal j_i with i=0 starting from the first undo-log block, comprising the first timestamp t_k/i which is the same as or occurs after timestamp t, till the first undo-log block comprising a timestamp t_k/i which is the same as or occurs after the first timestamp t_k/i+1 of the next journal j_i+1, with timestamp t_k/i+1 which is the same as or occurs after timestamp t;

repeating the preceding step of reading for all next journals j_i+1 with i=1, . . . , N−

2;

reading the last journal j<sub>N−

1</sub> starting from the first undo-log block comprising the first timestamp t<sub>k/N−

1</sub> which is the same as or occurs after timestamp t, till the end of journal j<sub>N−

1</sub>,

and in that

the data stored in an undo-log block read from a journal is only written to the corresponding segment of the data object, if said segment has not been re-written before, initiated by an undo-log block read before.

16. The method of claim 15, wherein a restore table is generated for each restore procedure listing the indexes j of those segments which have already been re-written.

17. The method of claim 15, wherein in case of an error, when reading journal j_i with 0<

i<

=N−

1,

journal j_i is removed;

all journals j_i+k+1 are renamed to be j_i+k with k=0, . . . , N−

i−

2 and all corresponding timestamps are renamed accordingly; and

reading continues with journal j<sub>i−

1</sub>.

18. The method of claim 15, wherein the offset-positions of the undo-log blocks to be read first in each journal j_i, are identified by means of an offset-table comprising for each timestamp t_k/i the offset-position for writing to the corresponding journal j_i after said timestamp t_k/i.

23. The infrastructure of claim 19, wherein the infrastructure is further capable of carrying out the steps of the method of claim 15.

19. An infrastructure for performing repetitive data protection and a corresponding restoration of data which is stored in a block oriented data object comprising several indexed segments, the infrastructure capable of carrying out the steps of:

setting timestamps t_k by a timer k;

recording only the first data modification of a segment, after a timestamp t_k has been set, by storing the old data contents of said segment together with the segment index j and said timestamp t_k as undo-log block in a first journal j₀ before overwriting said segment with the modified new data; and

transmitting said undo-log blocks to N journals j_i by storing redundant undo-log information, with N>

1 and i=1, . . . , N−

1;

said steps being characterized in that for each journal j_i journal-specific timestamps t_k/i are generated, so that each journal j_i is written for a different set of timestamps t_k/i,

the infrastructure comprising;

at least one block oriented data object;

a timer for setting timestamps;

an interceptor for holding the new data to be written to the data object until the old data to be overwritten is extracted for creating undo-log information;

N journals j_i for storing redundant undo-log information, with N>

1 and i=0, . . . , N−

1; and

a journaling component for generating undo-log blocks and writing them to multiple journals j_i;

wherein said journaling component comprises a splitter for writing each undo-log block to multiple journals and for generating for each journal j_i journal-specific timestamps t_k/i.

20. The infrastructure of claim 19, further comprising means for maintaining an offset-table, listing for each timestamp t_k/i the offset-position for writing to the corresponding journal j_i after said timestamp t_k/i.

21. The infrastructure of claim 19, further comprising means for maintaining a restore table listing the indexes j of those segments which have already been re-written in case of restore.