SNAPSHOTS FOR A NON-VOLATILE DEVICE

• US 20140089264A1
• Filed: 07/11/2013
• Published: 03/27/2014
• Est. Priority Date: 09/24/2012
• Status: Active Grant

• Current Assignee: SanDisk Technologies LLC (Western Digital Corporation)
• Original Assignee: Fusion-IO Incorporated (Western Digital Corporation)
• Inventors: Talagala, Nisha, Sundararaman, Swaminathan, Subramanian, Sriram
• Granted Patent: US 10,318,495 B2
• Time in Patent Office: Days
• US Class Current: 707/649
• CPC Class Codes: G06F 11/1448 Management of the data involved in backup or backup restore
• CPC Class Codes: G06F 11/1466 to make the backup process non-disruptive
• CPC Class Codes: G06F 11/1471 involving logging of persistent data for recovery
• CPC Class Codes: G06F 16/21 Design, administration or maintenance of databases
• CPC Class Codes: G06F 3/0616 in relation to life time, e.g. increasing Mean Time Between Failures [MTBF]
• CPC Class Codes: G06F 3/065 Replication mechanisms
• CPC Class Codes: G06F 3/0679 Non-volatile semiconductor memory device, e.g. flash memory, one time programmable memory [OTP]

Abstract

Apparatuses, systems, and methods are disclosed for snapshots of a non-volatile device. A method includes writing data in a sequential log structure for a non-volatile device. A method includes marking a point, in a sequential log structure, for a snapshot of data. A method includes preserving a logical-to-physical mapping for a snapshot based on a marked point and a temporal order for data in a sequential log structure.

Claims

1. A method comprising:

writing data in a sequential log structure on a non-volatile device;

marking a point, in the sequential log structure, for a snapshot of the data; and

preserving a logical-to-physical mapping for the snapshot based on the marked point and a temporal order for the data in the sequential log structure.

2. The method of claim 1, further comprising reconstructing the preserved logical-to-physical mapping by scanning the sequential log structure for stored logical identifiers and mapping the logical identifiers to physical locations that store the data.

3. The method of claim 1, further comprising maintaining different validity maps for a plurality of different snapshots of the non-volatile device.

4. The method of claim 3, wherein maintaining the different validity maps comprises copying at least a portion of a validity map for a first snapshot in response to a write request received for a second snapshot.

5. The method of claim 3, further comprising retaining, during a storage capacity recovery operation, data marked as valid in one or more of the different validity maps.

6. The method of claim 1, wherein building the logical-to-physical mapping is performed in response to an activation event for the snapshot, the activation event occurring separate from and later in time than a creation event for the snapshot.

7. The method of claim 6, wherein the activation event comprises one or more of an activation request for the snapshot, a background activation process processing the snapshot, a scheduled activation event for the snapshot, and a failure event.

8. The method of claim 1, wherein the snapshot comprises a block-level snapshot of logical blocks of the non-volatile device.

9. The method of claim 1, further comprising preserving the temporal order for the data in response to a storage capacity recovery event, the storage capacity recovery event writing valid data from a recovered storage region of the sequential log structure to an append point of the sequential log structure.

10. The method of claim 9, wherein preserving the temporal order for the data comprises retaining one or more epoch identifiers for the valid data written to the append point of the sequential log structure.

11. The method of claim 1, wherein marking the point in the sequential log structure comprises writing an epoch identifier associated with the snapshot to the sequential log structure.

12. The method of claim 1, wherein marking the point in the sequential log structure comprises incrementing an epoch identifier and storing the incremented epoch identifier in one or more metadata headers for data written in the sequential log structure after the point in the sequential log structure.

13. The method of claim 1, further comprising receiving a snapshot request for the snapshot and providing access to the snapshot of the data using the logical-to-physical mapping, wherein building the logical-to-physical mapping is in response to receiving the snapshot request.

14. An apparatus comprising:

a log storage module configured to store data sequentially to an append point of a chronologically ordered writing structure;

a creation module configured to initialize a snapshot in the chronologically ordered writing structure in response to a creation event for the snapshot; and

an activation module configured to activate the snapshot in response to an activation event for the snapshot, the activation module configured to activate the snapshot by processing the chronologically ordered writing structure to determine a logical-to-physical mapping structure for the snapshot.

15. The apparatus of claim 14, further comprising a validity module configured to maintain validity metadata for a plurality of different snapshots such that a storage capacity recovery operation retains valid data for the plurality of different snapshots based on the validity metadata.

16. The apparatus of claim 14, further comprising a snapshot tracking module configured to add an entry for the snapshot to a snapshot data structure, the snapshot data structure defining dependencies between a plurality of snapshots.

17. The apparatus of claim 14, further comprising a reconstruction module configured to process the chronologically ordered writing structure to reconstruct the snapshot data structure based on snapshot metadata written to the chronologically ordered writing structure by the creation module and to reconstruct an active logical-to-physical mapping structure for the chronologically ordered writing structure, each in response to a restart event.

18. The apparatus of claim 14, wherein the creation module is configured to initialize the snapshot by:

flushing pending data to the chronologically ordered writing structure; and

writing a snapshot-create indicator to the chronologically ordered writing structure.

19. An apparatus comprising:

means for preserving a temporal order of data in a sequential writing structure in the presence of storage capacity recovery operations for the sequential writing structure;

means for preserving a copy of data at a point in time in the sequential writing structure; and

means for activating the preserved copy at a later point in time based on the preserved temporal order of the data in the sequential writing structure.

20. The apparatus of claim 19, further comprising means for determining a logical-to-physical mapping structure and validity metadata for the preserved copy.