Replicating snapshots from a source storage system to a target storage system
View Patent ↗A source storage system replicates snapshots stored on the source storage system to a target storage system. The source storage system stores a plurality of snapshots. The source storage system also stores parent child relationships between snapshots. The source storage system allows child snapshots of a parent snapshot to be modified independent of each other. The source storage system determines changed blocks of a snapshot compared to a previously transmitted snapshot and sends only the changed blocks to the target storage system. The source storage system determines the changed blocks of a snapshot compared to a previously replicated snapshot based on time of creation of a common ancestor of two snapshots. The source storage system transmits a data block of a snapshot if either the data block or a corresponding data block of the previously replicated snapshot was modified after the creation of the common ancestor snapshot.
1. A method for transmitting a snapshot from a source system to a target system, the method comprising:
storing, in a source storage system, a plurality of snapshots, wherein a snapshot shares data blocks with one or more other snapshots stored in the source storage system;
maintaining parent-child relationships between snapshots if a child snapshot is created from a parent snapshot, wherein at least a parent snapshot has a parent child relationship with two or more child snapshots created from the parent snapshot, such that each child snapshot can be modified independent of the other child snapshots;
transmitting data of a first snapshot from the source storage system to a target storage system;
identifying a second snapshot to transmit from the source storage system to a target storage system, wherein the first snapshot and the second snapshot have a common ancestor snapshot such that both the first snapshot and the second snapshot are descendants of the common ancestor snapshot based on parent child relationships;
identifying data blocks of the second snapshot that are distinct from the first snapshot; and
transmitting the identified data blocks of the second snapshot to the target storage system.
2. The method of claim 1 , wherein identifying data blocks of the second snapshot that are distinct from the first snapshot is based on a comparison of the time of modification of one or more data blocks of the second snapshot with the time of creation of the common ancestor snapshot.
3. The method of claim 1 , wherein identifying data blocks of the second snapshot that are distinct from the first snapshot is based on a comparison of the time of modification of one or more data blocks of the first snapshot with the time of creation of the common ancestor snapshot.
4. The method of claim 1 , further comprising:
sending a data block of the second snapshot to the target storage system if the data block was modified after the time of creation of the common ancestor snapshot.
5. The method of claim 1 , further comprising:
sending a data block of the second snapshot to the target storage system if a corresponding data block of the first snapshot was modified after the time of creation of the common ancestor snapshot.
6. The method of claim 5 , wherein determining whether to transmit a data block of the second snapshot to the target storage system comprises:
comparing a checksum of the data block of the second snapshot with a checksum of the corresponding data block of the first snapshot; and
wherein the data block of the second snapshot is sent to the target storage system if the checksum of the data block of the second snapshot does not match the checksum of the corresponding data block of the first snapshot.
7. The method of claim 1 , wherein determining whether to transmit a data block of the second snapshot to the target storage system comprises determining not to send the data block to the target storage system if the time of modification of the data block is before the time of creation of the common ancestor snapshot.
8. The method of claim 1 , wherein the first snapshot includes a first set of data blocks modified after the creation of the ancestor snapshot and the second snapshot includes a second set of data blocks modified after the creation of the common ancestor snapshot, wherein the first set and the second set are non-overlapping.
9. The method of claim 1 , wherein identifying the common ancestor snapshot comprises identifying the most recent common ancestor snapshot.
10. The method of claim 1 , wherein a child snapshot corresponding to a parent snapshot is obtained by cloning the parent snapshot.
11. The method of claim 1 , wherein a child snapshot corresponding to a parent snapshot is obtained by applying a masking function to at least a portion of data of the parent snapshot.
12. The method of claim 1 , wherein a parent snapshot and a child snapshot have a parent child relationship if the parent snapshot and the child snapshot are two consecutive snapshots created in the source storage system.
13. A method for determining the differences between snapshots, the method comprising:
storing, in a source storage system, a plurality of snapshots, wherein a snapshot shares data blocks with one or more other snapshots stored in the source storage system;
maintaining parent-child relationships between snapshots if a child snapshot is created from a parent snapshot, wherein at least a parent snapshot has a parent child relationship with two or more child snapshots created from the parent snapshot, such that each child snapshot can be modified independent of the other child snapshots;
receiving a request to identify the differences between a first snapshot and a second snapshot;
identifying a common ancestor snapshot such that both the first snapshot and the second snapshot are descendants of the common ancestor snapshot based on the parent child relationships; and
determining that a data block of the second snapshot is different from a corresponding data block of the first snapshot based on a comparison of the time of modification of the data block and the time of creation of the common ancestor snapshot.
14. The method of claim 13 , further comprising:
determining that the data block of the second snapshot is different from the corresponding data block of the first snapshot if the time of modification of the data block is greater than the time of creation of the common ancestor snapshot.
15. The method of claim 13 , further comprising:
determining that the data block of the second snapshot is different from the corresponding data block of the first snapshot if the time of modification of the corresponding data block of the first snapshot is greater than the time of creation of the common ancestor snapshot.
16. The method of claim 15 , wherein determining whether a data block of the second snapshot is different from a corresponding data block of the first snapshot, comprises:
comparing a checksum of the data block of the second snapshot with a checksum of the corresponding data block of the first snapshot; and
wherein the data block of the second snapshot is determined to be different from the corresponding data block of the first snapshot if the checksum of the data block of the second snapshot does not match the checksum of the corresponding data block of the first snapshot.
17. The method of claim 13 , further comprising:
determining that the data block of the second snapshot is same as the corresponding data block of the first snapshot if the time of modification of the data block of the first snapshot is less than the time of creation of the common ancestor snapshot and the time of modification of the corresponding data block of the first snapshot is less than the time of creation of the common ancestor snapshot.
18. The method of claim 13 , wherein the first snapshot includes a first set of data blocks modified after the creation of the ancestor snapshot and the second snapshot includes a second set of data blocks modified after the creation of the common ancestor snapshot, wherein the first set and the second set are non-overlapping.
19. The method of claim 13 , wherein identifying the common ancestor snapshot comprises identifying the most recent common ancestor common snapshot.
20. The method of claim 13 , wherein a child snapshot corresponding to a parent snapshot is obtained by cloning the parent snapshot.
21. The method of claim 13 , wherein a parent snapshot and a child snapshot have a parent child relationship if the parent snapshot and the child snapshot are two consecutive snapshots created in the file system.
22. The method of claim 13 , wherein a child snapshot corresponding to a parent snapshot is obtained by applying a masking function to at least a portion of data of the parent snapshot.
23. A non-transitory computer-readable storage medium storing instructions for:
storing, in a source storage system, a plurality of snapshots, wherein a snapshot shares data blocks with one or more other snapshots stored in the source storage system;
maintaining parent-child relationships between snapshots if a child snapshot is created from a parent snapshot, wherein at least a parent snapshot has a parent child relationship with two or more child snapshots created from the parent snapshot, such that each child snapshot can be modified independent of the other child snapshots;
transmitting data of a first snapshot from the source storage system to a target storage system;
identifying a second snapshot to transmit from the source storage system to a target storage system, wherein the first snapshot and the second snapshot have a common ancestor snapshot such that both the first snapshot and the second snapshot are descendants of the common ancestor snapshot based on parent child relationships;
identifying data blocks of the second snapshot that are distinct from the first snapshot; and
transmitting the identified data blocks of the second snapshot to the target storage system.