Metadata Journaling with Error Correction Redundancy

• US 20140115232A1
• Filed: 10/23/2012
• Published: 04/24/2014
• Est. Priority Date: 10/23/2012
• Status: Active Grant

• Current Assignee: Seagate Technology LLC (Seagate Technology Holdings Plc)
• Original Assignee: Seagate Technology LLC (Seagate Technology Holdings Plc)
• Inventors: Goss, Ryan James, Seekins, David Scott, Gaertner, Mark Allen
• Granted Patent: US 9,411,717 B2
• Time in Patent Office: Days
• US Class Current: 711/103
• CPC Class Codes: G06F 11/1012 using codes or arrangements adapted for a specific type of error G06F11/1048 takes precedence
• CPC Class Codes: G06F 11/1471 involving logging of persistent data for recovery
• CPC Class Codes: G06F 12/0246 in block erasable memory, e.g. flash memory

Abstract

Method and apparatus for managing a memory, such as but not limited to a flash memory. In accordance with some embodiments, user data and associated metadata are stored in a memory. The metadata are arranged as a first sequence of snapshots of the metadata at different points in time during the operation of the memory, and a second sequence of intervening journals which reflect updates to the metadata from one snapshot to the next. Requested portions of the metadata are recovered from the memory using a selected snapshot in the first sequence and first and second journals in the second sequence.

Claims

1. A method comprising:

storing user data in a memory;

maintaining metadata in the memory associated with the stored user data, the metadata arranged as a first sequence of snapshots of the metadata at different points in time during the operation of the memory and a second sequence of intervening journals which reflect updates to the metadata from one snapshot to the next; and

recovering requested metadata from the memory using a selected snapshot in the first sequence and first and second intervening journals in the second sequence.

2. The method of claim 1, in which the first journal is formed prior to the selected snapshot and the second journal is formed after the second snapshot.

3. The method of claim 1, in which the first and second journals are both formed after the selected snapshot.

4. The method of claim 1, in which the first journal comprises error detection and correction (EDC) codes generated in accordance with a first EDC scheme, and the second journal comprises EDC codes generated in accordance with a second EDC scheme.

5. The method of claim 1, in which a selected one of the first or second EDC schemes is a parity code scheme.

6. The method of claim 1, in which a selected one of the first or second EDC schemes is a Reed-Solomon ECC scheme.

7. The method of claim 1, further comprising using the recovered metadata to to retrieve a selected block of the stored user data from the memory.

8. The method of claim 1, further comprising using the recovered metadata to write a new block of user data to the memory.

9. The method of claim 1, further comprising using the recovered metadata to schedule a garbage collection operation on a garbage collection unit (GCU) of the memory, the GCU allocated and erased as a unit.

10. The method of claim 1, in which data portions of the first and second journals are respectively retrieved from the memory and validated responsive to a comparison of said data portions.

11. The method of claim 10, further comprising retrieving data from a third journal associated with the first and second journals and applying error detection and correction (EDC) processing to the retrieved data from the third journal.

12. The method of claim 11, in which the EDC processing takes place concurrently with the comparison of the first and second journals and validating the first and second journals responsive to the EDC processing.

13. An apparatus comprising:

a memory arranged into a plurality of garbage collection units (GCUs) each separately allocated and erased as a unit, the memory storing user data in the form of addressable blocks and metadata that provide a logical to physical address correspondence for the user data, the metadata arranged as a first sequence of snapshots of the metadata at different points in time during the operation of the memory and a second sequence of intervening journals of updates to the metadata from one snapshot to the next; and

a metadata recovery engine adapted to recover selected metadata from the memory using a selected snapshot in the first sequence and first and second intervening journals in the second sequence.

14. The apparatus of claim 13, in which the selected snapshot is a most recent snapshot in the first sequence, the first and second journals are respective copies of updates to the metadata formed after the selected snapshot, and error detection and correction (EDC) codes are appended to a selected one of the first or second journals.

15. The apparatus of claim 13, in which the selected snapshot is a prior snapshot so that at least one other more recent snapshot is provided in the first sequence, and in which both the first and second snapshots were formed after the formation of the selected snapshot.

16. The apparatus of claim 13, further comprising a journal processing engine which generates first error detection and correction (EDC) codes for the first journal in accordance with a first EDC scheme and which generates different, second EDC codes for the second journal in accordance with a different, second EDC scheme.

17. The apparatus of claim 16, in which a selected one of the first or second EDC schemes is a parity code scheme.

18. The apparatus of claim 13, in which the metadata retrieval engine recovers respective data portions of the first and second journals and validates the data portions responsive to a comparison thereof.

19. The apparatus of claim 18, in which the metadata retrieval engine further operates to concurrently apply error detection and correction (EDC) processing to a third journal formed after the selected snapshot and to compare a result of said EDC processing to at least a selected one of the first or second journals.

20. The apparatus of claim 13, in which the memory is a flash memory and the GCUs are each formed from a plurality of erasure blocks.