Snapshot preserved data cloning
A method and device for cloning snapshots is provided. A new snapshot can be created by cloning an existing snapshot. The clone snapshot may use the preserved data of the existing snapshot, thereby obviating the need to copy the preserved data. Additionally, the clone snapshot may be created with a data structure for storing write data. Since the clone snapshot initially has no write data to store, the creation of the entire clone snapshot can be accomplished without copying any preserved data or write data from the existing snapshot, thereby increasing the efficiency with which a clone snapshot can be created.
1. A method of cloning a snapshot, comprising:
identifying a first snapshot of a storage volume, wherein the first snapshot corresponds to a first point-in-time capture of data on the storage volume, wherein the first snapshot comprises a first data structure for maintaining preserved data in association with the first snapshot and a second data structure for maintaining write data in association with the first snapshot;
altering a portion of the first snapshot after the first point-in-time;
creating a second snapshot that is a clone of the first snapshot and corresponds to the unaltered portion of the first snapshot; and
wherein the second snapshot references the preserved data of the first snapshot, wherein the second snapshot does not correspond to the altered portion of the first snapshot and the second snapshot comprises less data than the first snapshot.
2. The method of claim 1 , wherein altering the first snapshot comprises changing at least one of the preserved data and write data of the first snapshot.
3. The method of claim 1 , further comprising:
receiving a command to delete the first snapshot;
associating the preserved data of the first snapshot with the second snapshot; and deleting the write data of the first snapshot while leaving the preserved data for use in association with the second snapshot.
4. The method of claim 1 , wherein the second snapshot is initially created without write data, the method further comprising a host writing data directly to write data of the second snapshot.
5. The method of claim 1 , further comprising:
after creating the second snapshot, determining that a change to at least one block of data on the storage volume is desired;
performing a copy on write of the at least one block of data to the preserved data for the first snapshot; and
changing the at least one block of data on the storage volume.
6. The method of claim 1 , further comprising:
receiving a request to perform at least one of a read and a write operation with data corresponding to the second snapshot;
searching write data associated with the second snapshot;
in the event that the requested data is not located in the write data associated with the second snapshot, searching preserved data associated with the second snapshot;
in the event that the requested data is not located in both the write and preserved data associated with the second snapshot, searching preserved data associated with the first snapshot;
in the event that the requested data is not located in the write data associated with the second snapshot and the preserved data associated with either the first or second snapshot, searching at least one of preserved data associated with newer snapshots of the storage volume and the storage volume;
retrieving the requested data; and
performing at least one of the read and write operation.
7. The method of claim 6 , wherein the preserved data associated with the second snapshot is searched by searching the preserved data associated with the first snapshot.
8. The method of claim 1 , further comprising:
creating a third snapshot that is a clone of the second snapshot and corresponds to the unaltered portion of the first snapshot; and
wherein the first snapshot comprises preserved data and write data and wherein the third snapshot references preserved data of the second snapshot, which references the preserved data of the first snapshot.
9. The method of claim 8 , wherein an I/O application reads requested data from the first snapshot directly, wherein the I/O application forgoes reading the requested data from the second or third snapshots.
10. The method of claim 1 , wherein the second snapshot is created in response to storage controller instructions stored on a storage controller requesting creation of the second snapshot.