System and a method for generating live VM images with an extended recovery range

1. A method, comprising:

receiving, at an IO journal, a new entry that identifies a respective disk location L, and data X written at that disk location L;

determining whether a location specified in an oldest entry of the IO journal is specified in any other entries in the IO journal, and then:

when the location specified in the oldest entry is not specified in any other entries in the IO journal, adding the new entry to the IO journal, and augmenting the new entry with undo data; or

when the location specified in the oldest entry is specified in at least one other entry in the IO journal, setting data specified in the oldest entry as undo data for the next entry that identifies that location, and adding the new entry to the IO journal, wherein the undo data, when applied to a dataset, returns the dataset to a particular point in time; and

deleting the oldest entry from the IO journal,

wherein the IO journal is maintained at a fixed length, notwithstanding the adding and deleting of entries to the IO journal and the undo data is preserved without re-reading the undo data in the IO journal,

wherein the IO journal entries facilitate spinoff of a VM that is application-consistent at one or more particular points in time.

2. The method as recited in claim 1 , wherein the one or more particular points in time are before, and/or after, a VM backup image time.

3. The method as recited in claim 1 , wherein each entry in the IO journal corresponds to an IO that was written to a VM.

4. The method as recited in claim 1 , wherein the IO journal is continuously maintained for a stream of IOs.

5. The method as recited in claim 1 , wherein each entry in the IO journal specifies a location, and data written at that location as a result of an IO with which the entry is associated.

6. The method as recited in claim 1 , wherein the IO journal includes an entry with a timestamp prior to a time t when a backup image was taken of a VM with which the IO journal is associated.

7. The method as recited in claim 6 , wherein the time t is unknown when the entry with the timestamp prior to time t is received.

8. The method as recited in claim 1 , wherein the undo data is associated with the next entry, in chronological order, that identifies the same location as the oldest entry.

9. The method as recited in claim 1 , wherein a length of the IO journal remains constant, but a particular range of time spanned by the IO journal changes each time a new entry is added and the oldest entry is deleted.

10. The method as recited in claim 1 , wherein the IO journal is associated with a VM, and the operations further comprise taking a backup image of the VM during a time range spanned by the IO journal.

11. A non-transitory storage medium having stored therein instructions that are executable by one or more hardware processors to perform operations comprising:

receiving, at an IO journal, a new entry that identifies a respective disk location L, and data X written at that disk location L;

determining whether a location specified in an oldest entry of the IO journal is specified in any other entries in the IO journal, and then:

when the location specified in the oldest entry is not specified in any other entries in the IO journal, adding the new entry to the IO journal, and augmenting the new entry with undo data; or

when the location specified in the oldest entry is specified in at least one other entry in the IO journal, setting data specified in the oldest entry as undo data for the next entry that identifies that location, and adding the new entry to the IO journal, wherein the undo data, when applied to a dataset, returns the dataset to a particular point in time; and

deleting the oldest entry from the IO journal,

wherein the IO journal is maintained at a fixed length, notwithstanding the adding and deleting of entries to the IO journal and the undo data is preserved without re-reading the undo data in the IO journal,

wherein the IO journal entries facilitate spinoff of a VM that is application-consistent at one or more particular points in time.

12. The non-transitory storage medium as recited in claim 11 , wherein the one or more particular points in time are before, and/or after, a VM backup image time.

13. The non-transitory storage medium as recited in claim 11 , wherein each entry in the IO journal corresponds to an IO that was written to a VM.

14. The non-transitory storage medium as recited in claim 11 , wherein the IO journal is continuously maintained for a stream of IOs.

15. The non-transitory storage medium as recited in claim 11 , wherein each entry in the IO journal specifies a location, and data written at that location as a result of an IO with which the entry is associated.

16. The non-transitory storage medium as recited in claim 11 , wherein the IO journal includes an entry with a timestamp prior to a time t when a backup image was taken of a VM with which the IO journal is associated.

17. The non-transitory storage medium as recited in claim 16 , wherein the time t is unknown when the entry with the timestamp prior to time t is received.

18. The non-transitory storage medium as recited in claim 11 , wherein the undo data is associated with the next entry, in chronological order, that identifies the same location as the oldest entry.

19. The non-transitory storage medium as recited in claim 11 , wherein a length of the IO journal remains constant, but a particular range of time spanned by the IO journal changes each time a new entry is added and the oldest entry is deleted.

20. The non-transitory storage medium as recited in claim 11 , wherein the IO journal is associated with a VM, and the operations further comprise taking a backup image of the VM during a time range spanned by the IO journal.