ONLINE RECOVERY APPROACH TO SPACE ACCOUNTING

• US 20200133797A1
• Filed: 10/30/2018
• Published: 04/30/2020
• Est. Priority Date: 10/30/2018
• Status: Active Grant

• Current Assignee: Emc IP Holding Company LLC (Dell Technologies Inc.)
• Original Assignee: Emc IP Holding Company LLC (Dell Technologies Inc.)
• Inventors: Nanda, Kumari Bijayalaxmi, Patel, Dixit
• Granted Patent: US 11,023,333 B2
• Time in Patent Office: Days
• CPC Class Codes: G06F 11/1469 Backup restoration techniques
• CPC Class Codes: G06F 16/164 File meta data generation
• CPC Class Codes: G06F 2201/84 Using snapshots, i.e. a logical point-in-time copy of the data

Abstract

Techniques for performing online recovery of space accounting metadata. The techniques include reestablishing a plurality of counters for tracking amounts of physical storage space committed and/or unique to the volumes and/or volume families. The techniques include, while reestablishing the counters, conducting a tree walk through a mapping hierarchy of each volume and/or volume family, marking starting and ending points through the mapping hierarchy, and monitoring a logical offset from the starting point during the tree walk. Upon receipt of an IO request, the techniques determine whether the IO request and space accounting metadata recovery activities are attempting to access the same metadata based on the logical offset relative to the starting point, and update the counters and/or temporary versions of the counters, as appropriate. By providing such techniques, metadata inconsistencies can be addressed while allowing users of the data storage system full or at least partial access to their data.

Claims

1. A method of performing recovery of space accounting metadata while a data storage system is online for regular user data access, comprising:

in an online process, performing recovery of space accounting metadata of at least one data volume in a volume family, the performing of the recovery of space accounting metadata including accessing a region of metadata pertaining to the at least one data volume in the volume family, and maintaining corresponding metadata pertaining to the at least one data volume in the volume family;

receiving a storage IO request for servicing at the data storage system;

determining whether the servicing of the storage IO request includes accessing the same region of metadata being accessed in the recovery of space accounting metadata of the at least one data volume in the volume family; and

having determined that the servicing of the storage IO request includes accessing the same region of metadata as being accessed in the recovery of space accounting metadata of the at least one data volume in the volume family, permitting access to the region of metadata for servicing of the storage IO request, thereby assuring prompt access to data stored on the data storage system.

2. The method of claim 1 wherein the performing of the recovery of space accounting metadata of the at least one data volume in the volume family includes detecting a discrepancy in an amount of physical storage space committed to a respective data volume in a branch of the volume family.

3. The method of claim 2 wherein the performing of the recovery of space accounting metadata of the at least one data volume in the volume family further includes setting a starting point and an ending point for a tree walk through a mapping hierarchy to verify space accounting metadata for the respective data volume, the space accounting metadata corresponding to a first count representative of the amount of physical storage space committed to the respective data volume.

4. The method of claim 3 wherein the performing of the recovery of space accounting metadata of the at least one data volume in the volume family further includes maintaining corresponding space accounting metadata for the respective data volume, the maintained corresponding space accounting metadata corresponding to a newly calculated count representative of the amount of physical storage space committed to the respective data volume.

5. The method of claim 4 wherein the performing of the recovery of space accounting metadata of the at least one data volume in the volume family further includes performing the tree walk through the mapping hierarchy for the respective data volume from the starting point to the ending point.

6. The method of claim 5 wherein the performing of the recovery of space accounting metadata of the at least one data volume in the volume family further includes, upon receipt of the storage IO request, checking a current logical offset from the starting point for the tree walk, and wherein the determining of whether the servicing of the storage IO request includes accessing the same region of metadata being accessed in the recovery of space accounting metadata includes determining whether the servicing of the storage IO request includes accessing the same region of metadata being accessed in the recovery of space accounting metadata based on the current logical offset.

7. The method of claim 6 further comprising:

determining that the recovery of space accounting metadata of the at least one data volume in the volume family has proceeded past the region of metadata being accessed by the storage IO request; and

having determined that the recovery of space accounting metadata of the at least one data volume in the volume family has proceeded past the region of metadata being accessed by the storage IO request, updating the first count representative of the amount of physical storage space committed to the respective data volume, and updating the newly calculated count representative of the amount of physical storage space committed to the respective data volume.

8. The method of claim 6 further comprising:

determining that the recovery of space accounting metadata of the at least one data volume in the volume family has not proceeded past the region of metadata being accessed by the storage IO request; and

having determined that the recovery of space accounting metadata of the at least one data volume in the volume family has not proceeded past the region of metadata being accessed by the storage IO request, updating the first count representative of the amount of physical storage space committed to the respective data volume.

9. The method of claim 5 wherein the performing of the recovery of space accounting metadata of the at least one data volume in the volume family further includes checking a current logical offset from the starting point for the tree walk, and determining whether the recovery of space accounting metadata of the at least one data volume in the volume family has completed based on the current logical offset reaching the ending point for the tree walk.

10. The method of claim 9 wherein the performing of the recovery of space accounting metadata of the at least one data volume in the volume family further includes, having determined that the recovery of space accounting metadata of the at least one data volume in the volume family has completed, replacing the first count representative of the amount of physical storage space committed to the respective data volume with the newly calculated count representative of the amount of physical storage space committed to the respective data volume.

11. The method of claim 1 wherein the performing of the recovery of space accounting metadata of the at least one data volume in the volume family includes detecting a discrepancy in an amount of physical storage space committed or unique to the volume family.

12. The method of claim 11 wherein the performing of the recovery of space accounting metadata of the at least one data volume in the volume family further includes setting a starting point and an ending point for a tree walk through a mapping hierarchy to verify space accounting metadata for the volume family, the space accounting metadata corresponding to a count representative of the amount of physical storage space committed or unique to the volume family.

13. The method of claim 12 wherein the performing of the recovery of space accounting metadata of the at least one data volume in the volume family further includes maintaining corresponding space accounting metadata for the volume family, the maintained corresponding space accounting metadata corresponding to a newly calculated count representative of the amount of physical storage space committed or unique to the volume family.

14. The method of claim 13 wherein the performing of the recovery of space accounting metadata of the at least one data volume in the volume family further includes checking a current logical offset from the starting point for the tree walk, and determining whether the recovery of space accounting metadata of the volume family has completed based on the current logical offset reaching the ending point for the tree walk.

15. The method of claim 14 wherein the performing of the recovery of space accounting metadata of the at least one data volume in the volume family further includes, having determined that the recovery of space accounting metadata of the volume family has completed, replacing the count representative of the amount of physical storage space committed or unique to the volume family with the newly calculated count representative of the amount of physical storage space committed or unique to the volume family.

16. A data storage appliance configured to perform recovery of space accounting metadata while online for regular user data access, comprising:

at least one storage device configured to store a plurality of data volumes of a volume family;

a memory configured to store executable instructions; and

storage processing circuitry configured to execute the executable instructions out of the memory;

in an online process, to perform recovery of space accounting metadata of at least one data volume in the volume family, wherein performing of the recovery of space accounting metadata includes accessing a region of metadata pertaining to the at least one data volume in the volume family, and maintaining corresponding metadata pertaining to the at least one data volume in the volume family;

to receive a storage IO request;

to determine whether servicing of the storage IO request includes accessing the same region of metadata being accessed in the recovery of space accounting metadata of the at least one data volume in the volume family; and

having determined that the servicing of the storage IO request includes accessing the same region of metadata as being accessed in the recovery of space accounting metadata of the at least one data volume in the volume family, to permit access to the region of metadata for servicing of the storage IO request, thereby assuring prompt access to data stored on the data storage system.

17. The data storage appliance of claim 16 wherein the storage processing circuitry is further configured to execute the executable instructions out of the memory to detect a discrepancy in an amount of physical storage space committed to a respective data volume in a branch of the volume family.

18. The data storage appliance of claim 16 wherein the storage processing circuitry is further configured to execute the executable instructions out of the memory to detect a discrepancy in an amount of physical storage space committed to the volume family.

19. The data storage appliance of claim 16 wherein the storage processing circuitry is further configured to execute the executable instructions out of the memory to detect a discrepancy in an amount of physical storage space unique to the volume family.

20. A computer program product including a set of non-transitory, computer-readable media having instructions that, when executed by control circuitry of a computerized apparatus, cause the control circuitry to perform a method of performing recovery of space accounting metadata while a data storage system is online for regular user data access, the method comprising:

in an online process, performing recovery of space accounting metadata of at least one data volume in a volume family, the performing of the recovery of space accounting metadata including accessing a region of metadata pertaining to the at least one data volume in the volume family, and maintaining corresponding metadata pertaining to the at least one data volume in the volume family;

receiving a storage IO request for servicing at the data storage system;

determining whether the servicing of the storage IO request includes accessing the same region of metadata being accessed in the recovery of space accounting metadata of the at least one data volume in the volume family; and

having determined that the servicing of the storage IO request includes accessing the same region of metadata as being accessed in the recovery of space accounting metadata of the at least one data volume in the volume family, permitting access to the region of metadata for servicing of the storage IO request, thereby assuring prompt access to data stored on the data storage system.