STORAGE SYSTEM WITH SCANNING AND RECOVERY OF INTERNAL HASH METADATA STRUCTURES

• US 20200133794A1
• Filed: 10/25/2018
• Published: 04/30/2020
• Est. Priority Date: 10/25/2018
• Status: Active Grant

• Current Assignee: Emc IP Holding Company LLC (Dell Technologies Inc.)
• Original Assignee: Emc IP Holding Company LLC (Dell Technologies Inc.)
• Inventors: Shani, Nimrod, Fliess, Leron, Zohar, Tal
• Granted Patent: US 10,754,736 B2
• Time in Patent Office: Days
• CPC Class Codes: G06F 11/0751 Error or fault detection not based on redundancy power supply failures G06F1/30; network fault management H04L41/06
• CPC Class Codes: G06F 11/1435 using file system or storage system metadata
• CPC Class Codes: G06F 11/1464 for networked environments
• CPC Class Codes: G06F 11/1469 Backup restoration techniques
• CPC Class Codes: G06F 16/152 using file content signatures, e.g. hash values
• CPC Class Codes: G06F 16/2255 Hash tables
• CPC Class Codes: G06F 16/2365 Ensuring data consistency and integrity
• CPC Class Codes: G06F 2201/84 Using snapshots, i.e. a logical point-in-time copy of the data

Abstract

A storage system in one embodiment comprises a plurality of storage devices and a storage controller. The storage controller is configured to scan data pages and associated metadata structures of the storage system, the metadata structures comprising at least a first metadata structure associating unique hash identifiers with physical locations of respective data pages in the storage system and a second metadata structure associating the physical locations of respective data pages with hash digests of the data pages and the unique hash identifiers. The storage controller is further configured to detect an error in one of the first and second metadata structures. Responsive to the detected error, the storage controller recovers a corresponding portion of the metadata based at least in part on one or more entries of the other one of the first and second metadata structures. The unique hash identifiers illustratively comprise respective shortened representations of the hash digests, such as hash handles uniquely corresponding to respective ones of the hash digests.

Claims

1. An apparatus comprising:

a storage system comprising a plurality of storage devices and a storage controller;

the storage controller being configured;

to scan data pages and associated metadata structures of the storage system, the metadata structures comprising at least a first metadata structure associating unique hash identifiers with physical locations of respective data pages in the storage system and a second metadata structure associating the physical locations of respective data pages with hash digests of the data pages and the unique hash identifiers;

to detect an error in one of the first and second metadata structures; and

responsive to the detected error, to recover a corresponding portion of the metadata based at least in part on one or more entries of the other one of the first and second metadata structures;

wherein the storage controller comprises at least one processing device comprising a processor coupled to a memory.

2. The apparatus of claim 1 wherein the first metadata structure comprises a first metadata table, the first metadata table comprising a plurality of entries accessible utilizing the unique hash identifiers as respective keys, with each such entry of the first metadata table comprising a corresponding one of the unique hash identifiers, a corresponding reference count and a corresponding physical offset of one of the data pages.

3. The apparatus of claim 1 wherein the second metadata structure comprises a second metadata table, the second metadata table comprising a plurality of entries accessible utilizing physical offsets of the physical locations as respective keys, with each such entry of the second metadata table comprising a corresponding one of the physical offsets, a corresponding one of the hash digests, and a corresponding one of the unique hash identifiers.

4. The apparatus of claim 1 wherein the unique hash identifiers are shorter in length than the corresponding hash digests of the respective data pages.

5. The apparatus of claim 4 wherein the unique hash identifiers comprise respective hash handles of the data pages with the hash handles uniquely corresponding to respective ones of the hash digests.

6. The apparatus of claim 1 wherein the storage controller is further configured to initiate the scanning of the data pages and the metadata structures responsive to a metadata loss event.

7. The apparatus of claim 1 wherein the storage controller is further configured to scan the data pages and the metadata structures by:

identifying a range of data pages to be scanned;

for each of the data pages in the identified range;

computing a hash digest of the page;

utilizing the computed hash digest to identify a corresponding entry of the first metadata structure;

executing a first comparison of an actual physical location of the page with the corresponding entry of the first metadata structure;

executing a second comparison of the computed hash digest of the page to a corresponding entry of the second metadata structure;

wherein an error in the first metadata structure is indicated by an inconsistency between the actual physical location of the page and the corresponding entry of the first metadata structure in the first comparison; and

wherein an error in the second metadata structure is indicated by an inconsistency between the computed hash digest of the page and the corresponding entry of the second metadata structure in the second comparison.

8. The apparatus of claim 7 wherein responsive to detection of an error in the first metadata structure, the corresponding entry of the first metadata structure is recovered at least in part by:

obtaining the unique hash identifier from the second metadata structure; and

generating an updated entry based at least in part on the unique hash identifier.

9. The apparatus of claim 7 wherein responsive to detection of an error in the second metadata structure, the corresponding entry of the second metadata structure is recovered at least in part by:

obtaining the unique hash identifier from the first metadata structure; and

generating an updated entry based at least in part on the unique hash identifier and the computed hash digest.

10. The apparatus of claim 1 wherein the hash digests are computed by applying a secure hashing algorithm to content of the respective data pages.

11. The apparatus of claim 1 wherein the storage system is implemented in the form of a clustered storage system comprising a plurality of nodes, each of at least a subset of the nodes comprising:

a processor coupled to a memory; and

a set of processing modules configured to communicate over one or more networks with corresponding sets of processing modules on other ones of the nodes.

12. The apparatus of claim 11 wherein the sets of processing modules collectively comprise at least a portion of a distributed implementation of the storage controller of the storage system.

13. The apparatus of claim 11 wherein at least one of the sets of processing modules comprises at least one system-wide management module implemented on a corresponding one of the nodes.

14. The apparatus of claim 11 wherein the sets of processing modules of at least a subset of the nodes each comprise at least one control module and at least one data module, with different portions of a logical address space of the storage system being assigned to different ones of the control modules, each of the control modules being configured to direct received write requests to particular ones of the data modules for storage of corresponding data pages in particular ones of the storage devices.

15. A method comprising:

scanning data pages and associated metadata structures of a storage system, the metadata structures comprising at least a first metadata structure associating unique hash identifiers with physical locations of respective data pages in the storage system and a second metadata structure associating the physical locations of respective data pages with hash digests of the data pages and the unique hash identifiers;

detecting an error in one of the first and second metadata structures; and

responsive to the detected error, recovering a corresponding portion of the metadata based at least in part on one or more entries of the other one of the first and second metadata structures;

wherein the method is implemented by at least one processing device comprising a processor coupled to a memory.

16. The method of claim 15 wherein the first metadata structure comprises a first metadata table, the first metadata table comprising a plurality of entries accessible utilizing the unique hash identifiers as respective keys, with each such entry of the first metadata table comprising a corresponding one of the unique hash identifiers, a corresponding reference count and a corresponding physical offset of one of the data pages.

17. The method of claim 15 wherein the second metadata structure comprises a second metadata table, the second metadata table comprising a plurality of entries accessible utilizing physical offsets of the physical locations as respective keys, with each such entry of the second metadata table comprising a corresponding one of the physical offsets, a corresponding one of the hash digests, and a corresponding one of the unique hash identifiers.

18. A computer program product comprising a non-transitory processor-readable storage medium having stored therein program code of one or more software programs, wherein the program code when executed by at least one processing device causes said at least one processing device:

to scan data pages and associated metadata structures of a storage system, the metadata structures comprising at least a first metadata structure associating unique hash identifiers with physical locations of respective data pages in the storage system and a second metadata structure associating the physical locations of respective data pages with hash digests of the data pages and the unique hash identifiers;

to detect an error in one of the first and second metadata structures; and

responsive to the detected error, to recover a corresponding portion of the metadata based at least in part on one or more entries of the other one of the first and second metadata structures.

19. The computer program product of claim 18 wherein the first metadata structure comprises a first metadata table, the first metadata table comprising a plurality of entries accessible utilizing the unique hash identifiers as respective keys, with each such entry of the first metadata table comprising a corresponding one of the unique hash identifiers, a corresponding reference count and a corresponding physical offset of one of the data pages.

20. The computer program product of claim 18 wherein the second metadata structure comprises a second metadata table, the second metadata table comprising a plurality of entries accessible utilizing physical offsets of the physical locations as respective keys, with each such entry of the second metadata table comprising a corresponding one of the physical offsets, a corresponding one of the hash digests, and a corresponding one of the unique hash identifiers.