SEQUENCING TECHNIQUE TO ACCOUNT FOR A CLOCK ERROR IN A BACKUP SYSTEM

• US 20100023797A1
• Filed: 07/25/2008
• Published: 01/28/2010
• Est. Priority Date: 07/25/2008
• Status: Active Grant

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: InMage Systems, Inc. (Microsoft Corporation)
• Inventors: SHAH, Jayesh, ATLURI, Rajeev, KUMAR, Srin, LANKA, Sridhara, KUMAR, Satish
• Granted Patent: US 8,028,194 B2
• Time in Patent Office: Days
• US Class Current: 714/2
• CPC Class Codes: G06F 11/0727 in a storage system, e.g. in a DASD or network based storage system drivers for digital recording or reproducing units G06F3/06; circuits for error detection or correction within digital recording or reproducing units G11B20/18; for distributed storage of data in networks, e.g. transport arrangements for network file system [NFS], storage area networks [SAN] or network attached storage [NAS], H04L67/1097
• CPC Class Codes: G06F 11/0751 Error or fault detection not based on redundancy power supply failures G06F1/30; network fault management H04L41/06
• CPC Class Codes: G06F 11/1464 for networked environments
• CPC Class Codes: G06F 2201/82 Solving problems relating to consistency ensuring consistency in mirrored systems G06F11/2064
• CPC Class Codes: G06F 2201/835 Timestamp

Abstract

A method, apparatus, and system of a sequencing technique to account for a clock error in a storage area network are disclosed. In one embodiment, a system of a backup server includes a processing module to examine a data timestamped with a sequence of characters denoting a time according to a clock source, an analysis module to determine that the data has been timestamped at an earlier time than an other data previously received, a substitution module to provide the data an incremental sequence number placed with the data using an algorithm until a new data is received that includes a future timestamp with a later timestamp than the timestamp of the other data, and a storage module to store the data.

Claims

1. A system of a backup server, comprising:

a processing module to examine a data timestamped with a sequence of characters denoting a time according to a clock source;

an analysis module to determine that the data has been timestamped at an earlier time than an other data previously received; and

a substitution module to provide the data an incremental sequence number placed with the data using an algorithm until a new data is received that includes a future timestamp with a later timestamp than a timestamp of the other data; and

a storage module to store the data.

2. The system of claim 1 wherein a sequence number is a global sequence number that increments across a plurality of sources of the data, and wherein the sequence number is changed based on an event in a network associated with the backup server, wherein the event is at least one of a write I/O being received and a shutdown event in the network.

3. The system of claim 2 wherein the global sequence number is used for the new data received when the timestamp of the data timestamped with a sequence of numbers is unavailable.

4. The system of claim 1 wherein the sequence number is an incremental value timestamp generated by incrementing the timestamp of the other data previously received.

5. The system of claim 4 further comprising:

a setting module to reset the incremental sequence number to a first value when the new data is received that includes the future timestamp with the later timestamp than the timestamp of the other data.

6. The system of claim 1 wherein the sequence number is a relative time interval value placed with the timestamp of the other data denoting a relative time interval according to an independent clock source.

7. The system of claim 1, further comprising:

wherein the storage module to store the data in a continuous data protection repository for a threshold value such that the data is persistently stored, wherein the threshold value is an amount of time, an allocated storage space, an available storage space.

8. The system of claim 7, further comprising:

an association module to associate the incremental sequence number with an equivalent timestamp; and

a sequence module to algorithmically determine a chronological sequence and arrange a set of data based on successive ones of the incremental sequence number and another set of data not based on successive ones of the incremental sequence number according to the chronological sequence.

9. The system of claim 8, further comprising:

a collation module to collate a plurality of sets of data based on successive ones of the incremental sequence number of a plurality of storage modules and a plurality of the sets of data not based on successive ones of the incremental sequence number of the plurality of storage modules according to the chronological sequence

10. The system of claim 9, further comprising:

a retrieval module to access the data stored according to the chronological sequence through a lookup algorithm that examines the timestamp of the other data to determine an accurate location of a target data in a data stream between the other data and a plurality of sequence numbers to recover at least one of a within a volume and across volumes to the accurate location of the target data, and when a granularity of an increment of a timestamp cannot be used to delineate an order of an I/O, then the sequence number is also used to determine the accurate location.

11. The system of claim 1 in a form of a machine-readable medium embodying a set of instructions that, when executed by a machine, causes the machine to perform the according to the system of claim 1.

12. A system of a backup server, comprising:

an interface module to collect a data packet with a timestamp from a computer network;

a monitor module to determine if the timestamp is received from the computer network in a proper chronological sequence by comparing the timestamp to a previously received timestamp;

an identifier module to affix a relative sequential identifier to the previously received timestamp when a subsequent timestamp is received from the computer network with a chronological value that is less than the previously received timestamp and until a later timestamp is received from the computer network with the chronological value that is greater than the previously received timestamp ; and

a write module to store the data packet to a data storage medium.

13. The system of claim 12, further comprising:

a comparison module to equate the timestamp with the relative sequential identifier with a corresponding timestamp.

14. The system of claim 13, further comprising:

an assembly module to assemble a set of data packets with timestamps with the relative sequential identifier with the set of data packets with timestamps without the relative sequential identifier into the proper chronological sequence.

15. The system of claim 14, further comprising:

a synchronization module to chronologically synchronize the plurality of data packets of a plurality of data storage mediums into the proper chronological sequence.

16. A method of storing data comprising:

examining a data timestamped with a sequence of characters denoting a time according to a clock source;

determining that the data has been timestamped at an earlier time than an other data previously received;

providing the data an incremental sequence number generated by incrementing the timestamp of the other data previously received until a new data is received that includes a future timestamp with a later timestamp than the timestamp of the other data; and

storing the data.

17. The method of claim 16, wherein the incremental sequence number is an incremental number placed with the data.

18. The method of claim 17, further comprising:

resetting the incremental sequence number to a first value when a new data is received that includes a future timestamp with the later timestamp than the timestamp of the other data.

19. The method of claim 18, wherein the incremental sequence number is a relative time interval value placed with the timestamp of the other data denoting a relative time interval according to an independent clock source.

20. The method of claim 18, further comprising:

associating the incremental sequence number with an equivalent timestamp.

21. The method of claim 20, further comprising:

algorithmically determining a chronological sequence and arranging a set of data based on successive ones of the incremental sequence number and another set of data not based on successive ones of the incremental sequence number according to the chronological sequence.

22. The method of claim 21, further comprising:

retrieving the data stored according to a chronological sequence.

23. A method of a backup server comprising:

algorithmically locating a time stamp time nearest to a user specified time within a set of storage modules;

algorithmically mapping a global sequence number with the user specified time; and

algorithmically locating a proceeding global sequence number of an incremental sequence of global sequence numbers across other storage modules of the set of storage modules until a set of required global sequence numbers of the storage modules have been identified that correspond to the user specified time.

24. The method of claim 24 further comprising using an approximation algorithm to use the global sequence number as an equivalent of a specified number of clock ticks.

25. The method of claim 25 further comprising mapping a user specified event to the user specified time.