Conversion between full-data and space-saving snapshots
View Patent ↗A method, system, computer system, and computer-readable medium that enable a copy of data to be converted from a full-data snapshot to a space-saving snapshot, or vice versa, while retaining all the contents of the snapshot. Full-data snapshots can be used for efficient read operations and off-host processing operations. Space-saving snapshots can be used to store multiple copies of primary data in a minimum amount of storage space without consuming unnecessary storage space to store duplicate copies of data that are not changing. The ability to convert between full-data and space-saving snapshots enables organizational storage, backup, and recovery needs to be met using the best type of snapshot for a given operation.
1. A method comprising:
converting between a full-data snapshot and a space-saving snapshot, wherein
the full-data snapshot comprises memory to store data for each region of a plurality of regions of primary data, and
the space-saving snapshot comprises memory to store data for each changed region of the plurality of regions of the primary data, wherein
memory to store data for a first region of the plurality of regions is allocated to the space-saving snapshot in response to a change to the primary data in the first region, and
no memory is allocated to the space-saving snapshot for a second region of the plurality of regions if no change to the primary data in the second region occurs.
2. The method of claim 1 wherein
converting from the full-data snapshot to the space-saving snapshot comprises:
identifying a first set of regions of the plurality of regions, wherein
each region in the first set has primary data that have changed since a point in time;
allocating memory in the space-saving snapshot for each region in the first set of regions; and
copying an original value for the primary data of each region in the first set of regions from the full-data snapshot to the space-saving snapshot.
3. The method of claim 2 further comprising:
identifying a second set of regions of the primary data, wherein
each region in the second set has primary data that have not changed since the point in time; and
freeing memory previously allocated for the second set of regions in the full-data snapshot.
4. The method of claim 2 further comprising:
marking each region in the space-saving snapshot as valid in the full-data snapshot; and
after each region in the space-saving snapshot is marked in the full-data snapshot,
marking each unmarked region in the full-data snapshot as invalid in the full-data snapshot.
5. The method of claim 1 wherein converting from the space-saving snapshot to the full-data snapshot comprises:
allocating memory to store the primary data to the full-data snapshot;
saving valid data from the space-saving snapshot in the full-data snapshot; and
copying data for regions with no data in the space-saving snapshot from a parent of the space-saving snapshot to the full-data snapshot.
6. The method of claim 5 further comprising:
constructing the full-data snapshot as an instant full-data snapshot by performing the following:
after the valid data are saved in the full-data snapshot, making the full-data snapshot available; and
performing the copying of the data for the regions with no data from the parent into the full-data snapshot while the full-data snapshot is available.
7. The method of claim 5 wherein
the parent of the space-saving snapshot comprises the primary data.
8. The method of claim 5 further comprising:
marking each region in the full-data snapshot as valid.
9. A computer-readable storage medium comprising:
converting instructions, executable by a processor, and configured to convert between a full-data snapshot and a space-saving snapshot, wherein
the full-data snapshot comprises memory to store data for each region of a plurality of regions of primary data, and
the space-saving snapshot comprises memory to store data for each changed region of the plurality of regions of the primary data, wherein
memory to store data for a first region of the plurality of regions is allocated to the space-saving snapshot in response to a change to the primary data in the first region, and
no memory is allocated to the space-saving snapshot for a second region of the plurality of regions if no change to the primary data in the second region occurs.
10. The computer-readable storage medium of claim 9 further comprising:
first converting instructions, executable by the processor, and configured to convert from the full-data snapshot to the space-saving snapshot, wherein the first instructions comprise:
identifying instructions, executable by the processor, and configured to identify a first set of regions of the plurality of regions, wherein
each region in the first set has primary data that have changed since a point in time;
allocating instructions, executable by the processor, and configured to allocate memory in the space-saving snapshot for each region in the first set of regions; and
copying instructions, executable by the processor, and configured to copy an original value for the primary data of each region in the first set of regions from the full-data snapshot to the space-saving snapshot.
11. The computer-readable storage medium of claim 10 further comprising:
second identifying instructions, executable by the processor, and configured to identify a second set of regions of the primary data, wherein
each region in the second set has primary data that have not changed since the point in time; and
freeing instructions, executable by the processor, and configured to free memory previously allocated for the second set of regions in the full-data snapshot.
12. The computer-readable storage medium of claim 9 further comprising:
first marking instructions, executable by the processor, and configured to mark each region in the space-saving snapshot as valid in the full-data snapshot; and
second marking instructions, executable by the processor, and configured to perform the following:
after each region in the space-saving snapshot is marked in the full-data snapshot, mark each unmarked region in the full-data snapshot as invalid in the full-data snapshot.
13. The computer-readable storage medium of claim 9 further comprising:
second converting instructions, executable by the processor, and configured to convert from the space-saving snapshot to the full-data snapshot, wherein the second instructions comprise:
allocating instructions, executable by the processor, and configured to allocate memory to store the primary data to the full-data snapshot;
saving instructions, executable by the processor, and configured to save valid data from the space-saving snapshot in the full-data snapshot; and
copying instructions, executable by the processor, and configured to copy data for regions with no data in the space-saving snapshot from a parent of the space-saving snapshot to the full-data snapshot.
14. The computer-readable storage medium of claim 13 further comprising:
constructing instructions, executable by the processor, and configured to construct the full-data snapshot as an instant full-data snapshot by performing the following:
after the valid data are saved in the full-data snapshot, making the full-data snapshot available; and
performing the copying of the data for the regions with no data from the parent into the full-data snapshot while the full-data snapshot is available.
15. The computer-readable storage medium of claim 13 wherein the parent of the space-saving snapshot comprises the primary data.
16. The computer-readable storage medium of claim 13 further comprising:
marking instructions, executable by the processor, and configured to mark each region in the full-data snapshot as valid.
17. A system comprising:
first converting means for converting between a full-data snapshot and a space-saving snapshot, wherein
the full-data snapshot comprises memory to store data for each region of a plurality of regions of primary data, and
the space-saving snapshot comprises memory to store data for each changed region of the plurality of regions of the primary data, wherein
memory to store data for a first region of the plurality of regions is allocated to the space-saving snapshot in response to a change to the primary data in the first region, and
no memory is allocated to the space-saving snapshot for a second region of the plurality of regions if no change to the primary data in the second region occurs; and
second converting means for converting from the full-data snapshot to the space-saving snapshot.
18. The system of claim 17 , wherein the second converting means comprise:
identifying instructions to identify a first set of regions of the plurality of regions, wherein
each region in the first set has primary data that have changed since a point in time;
allocating instructions to allocate memory in the space-saving snapshot for each region in the first set of regions; and
copying instructions to copy an original value for the primary data of each region in the first set of regions from the full-data snapshot to the space-saving snapshot.
19. The system of claim 17 further comprising:
third converting means for converting from the space-saving snapshot to the full-data snapshot.
20. The system of claim 19 , wherein the third converting means comprise:
allocating means for allocating memory to store the primary data to the full-data snapshot;
saving means for saving valid data from the space-saving snapshot in the full-data snapshot; and
copying means for copying data for regions with no data in the space-saving snapshot from a parent of the space-saving snapshot to the full-data snapshot.
21. A system comprising:
a converting module to convert between a full-data snapshot and a space-saving snapshot, wherein
the full-data snapshot comprises memory to store data for each region of a plurality of regions of primary data, and
the space-saving snapshot comprises memory to store data for each changed region of the plurality of regions of the primary data, wherein
memory to store data for a first region of the plurality of regions is allocated to the space-saving snapshot in response to a change to the primary data in the first region, and
no memory is allocated to the space-saving snapshot for a second region of the plurality of regions if no change to the primary data in the second region occurs.
22. The system of claim 21 further comprising:
a second converting module to convert from the full-data snapshot to the space-saving snapshot, wherein the second converting module comprises:
identifying instructions to identify a first set of regions of the plurality of regions, wherein
each region in the first set has primary data that have changed since a point in time;
allocating instructions to allocate memory in the space-saving snapshot for each region in the first set of regions; and
copying instructions to copy an original value for the primary data of each region in the first set of regions from the full-data snapshot to the space-saving snapshot.
23. The system of claim 21 further comprising:
a second converting module to convert from the space-saving snapshot to the full-data snapshot, wherein the second converting module comprises:
allocating instructions to allocate memory to store the primary data to the full-data snapshot;
saving instructions to save valid data from the space-saving snapshot in the full-data snapshot; and
copying instructions to copy data for regions with no data in the space-saving snapshot from a parent of the space-saving snapshot to the full-data snapshot.