Unlimited file system snapshots and clones

• US 20070106706A1
• Filed: 08/31/2006
• Published: 05/10/2007
• Est. Priority Date: 11/04/2005
• Status: Active Grant

• Current Assignee: Oracle America, Inc. (Oracle Corporation)
• Original Assignee: Sun Microsystems Incorporated (Oracle Corporation)
• Inventors: Ahrens, Matthew, Maybee, Mark, Bonwick, Jeffrey
• Granted Patent: US 8,549,051 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G06F 16/128 Details of file system snapshots on the file-level, e.g. snapshot creation, administration, deletion use of snapshots for error detection or correction G06F11/14, G06F11/16

Abstract

The invention relates to a system that includes a file system configured to create a snapshot of a hierarchical block tree (HBT) and a storage pool. After the snapshot has been created, the storage pool includes a snapshot, where the snapshot includes a copy of a first version of a root block and the HBT, where the HBT includes a second version of the root block. Further, the copy of the first version of the root block is created prior to overwriting the first version of the root block with the second version of the root block, the second version of the root block comprises references to a first block and a second block, and the copy of the first version of the root block comprises a reference to the first block and no reference to the second block.

Claims

1. A system, comprising:

a file system configured to create a snapshot of a hierarchical block tree (HBT);

a storage pool, after the snapshot has been created, comprises;

the snapshot comprising a copy of a first version of a root block,

the HBT comprising a second version of the root block; and

wherein the copy of the first version of the root block is created prior to overwriting the first version of the root block with the second version of the root block,

wherein the second version of the root block comprises references to a first block and a second block;

wherein the copy of the first version of the root block comprises a reference to the first block and no reference to the second block.

2. The system of claim 1, wherein the file system is further configured to create a clone of the snapshot, wherein the clone of the snapshot initially consists of a clone root block, wherein the clone root block corresponds to the copy of the first version of the root block.

3. The system of claim 2, wherein the file system is configured to perform at least one action selected from a group consisting of adding an additional block to the clone and deleting an existing block from the clone, and wherein performing the at least one selected action does not alter the HBT.

4. The system of claim 3, wherein adding the additional block to the clone comprises overwriting the clone root block to obtain a modified clone root block, wherein the modified clone root block comprises a reference to the additional block.

5. The system of claim 4, wherein the modified clone root block directly references the additional block.

6. The system of claim 3, wherein deleting the existing block comprises overwriting the clone root block to obtain a modified clone root block, wherein the modified clone root block does not comprise a reference to the existing block.

7. The system of claim 2, wherein the copy of the first version of the root block and the second version of the root block are linked to each other using a doubly-linked list.

8. The system of claim 2, wherein the clone root block is linked to the copy of the first version of the root block using a pointer.

9. The system of claim 2, wherein the snapshot is associated with a reference count and wherein the reference count is incremented when the clone of the snapshot is created.

10. The system of claim 2, wherein the snapshot is associated with a reference count and wherein the reference count is decremented when the clone of the snapshot is deleted.

11. The system of claim 1, wherein the HBT is associated with a dead list, wherein the dead list comprises a block referenced in the snapshot and not currently referenced in HBT.

12. The system of claim 11, wherein a block is referenced by the snapshot if a birth time associated with the block is earlier than the birth time associated with the snapshot.

13. The system of claim 12, wherein the birth time of the snapshot corresponds to the birth time of the first version of the root block.

14. The system of claim 1, wherein the snapshot is associated with a dead list and wherein contents of the dead list initially corresponds to content of a dead list associated with the HBT prior to overwriting the first version of the root block with the second version of the root block

15. A computer readable medium comprising computer executable instructions for creating a snapshot of a hierarchical block tree (HBT), the executable instructions comprising:

instructions for obtaining a copy of a first version of a root block of the HBT prior to overwriting the first version of the root block with a second version of the root block;

instructions for designating the copy of a first version of a root block as a root block of the snapshot;

instructions for associating a dead list of the HBT with the snapshot;

instructions for overwriting the first version of the root block with a second version of the root block; and

instructions for associating the HBT with an empty dead list, wherein the HBT comprises the second version of the root block.

16. The computer readable medium of claim 15, further comprising:

instructions for creating a clone of the snapshot, wherein the clone of the snapshot initially consists of a clone root block, wherein the clone root block corresponds to the copy of the first version of the root block.

17. The computer readable medium of claim 16, further comprising:

instructions to perform at least one action selected from a group consisting of adding an additional block to the clone and deleting an existing block from the clone,

wherein performing the at least one selected action does not alter the HBT,

wherein adding the additional block to the clone comprises overwriting the clone root block to obtain a first modified clone root block and the first modified clone root block comprises a reference to the additional block, and

wherein deleting the existing block comprises overwriting the clone root block to obtain a second modified clone root block, wherein the second modified clone root block does not comprise a reference to the existing block.

18. The computer readable medium of claim 17, further comprising:

instructions for creating a snapshot of the clone, wherein the snapshot of the clone initially consists of a clone snapshot root block, wherein the clone snapshot root block corresponds to a copy of one selected from a group consisting of the first modified clone root block and the second modified clone root block.

19. The computer readable medium of claim 16, further comprising:

instructions for incrementing a reference count when the clone is created; and

instructions for decrementing when the clone of the snapshot is deleted,

wherein the reference count is associated with the snapshot.

20. The computer readable medium of claim 15, further comprising:

instructions for updating the deadline associated with the HBT, wherein the dead list is updated when a block referenced by root block of the snap shot ceases to be referenced by the second version of the root block.