Systems and methods for a snapshot of data

• US 20080046432A1
• Filed: 08/18/2006
• Published: 02/21/2008
• Est. Priority Date: 08/18/2006
• Status: Active Grant

• Current Assignee: Emc IP Holding Company LLC (Dell Technologies Inc.)
• Original Assignee: EMC Corporation (Dell Technologies Inc.)
• Inventors: Schack, Darren P., Passey, Aaron J., Lemar, Eric M., Anderson, Robert J., Fachan, Neal T., Richards, David W.
• Granted Patent: US 7,953,704 B2
• Time in Patent Office: Days
• US Class Current: 707/8
• 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
• CPC Class Codes: G06F 16/174 Redundancy elimination performed by the file system management of the data involved in backup or backup restore using de-duplication of the data G06F11/14

Abstract

In one embodiment, a user or client device is connected to a distributed file system comprised of one or more physical nodes. The data on each of the physical nodes store metadata about files and directories within the file system. Some of the embodiments permit a user to take a snapshot of data stored on the file system. The snapshot may include a single file, a single directory, a plurality of files within a directory, a plurality of directories, a path on the file system that includes nested files and subdirectories, or more than one path on the file system that each includes nested files and directories.

Claims

1. A method for taking a snapshot of a portion of a file system including files and directories, comprising:

accepting at least one path that represents a portion of a file system where the portion is less than the entire file system;

retrieving at least one data structure that represents the top-most level of the at least one path; and

prior to any modifications of the portion of the file system represented by the at least one path, indicating in the at least one data structure that the at least one path is governed by a snapshot.

2. The method of claim 1, wherein a plurality of snapshots are each created in substantially the same amount of time, irrespective of the size of the portion of the file system governed by each of the plurality of snapshots.

3. The method of claim 1, wherein a plurality of snapshots are each created using the same number of operations, irrespective of the size of the portion of the file system governed by each of the plurality of snapshots.

4. The method of claim 1, further comprising:

receiving a request to modify a modified data structure;

determining that the modified data structure is governed by the snapshot;

copying metadata associated with the modified data structure into a snapshot metadata structure prior to modifying the modified data structure.

5. The method of claim 1, further comprising:

receiving a request to modify a portion of a file;

determining that the file is governed by the snapshot;

copying the portion of the file into a file snapshot data structure, prior to modifying the file;

creating an at least one indication in the file snapshot data structure that indicates that unmodified portions of the file can be found elsewhere; and

modifying the file.

6. The method of claim 1, further comprising:

creating a mini-snap data structure, wherein the mini-snap data structure includes a portion of information about the corresponding level of the file system and can be used to traverse the file system to the at least one path, wherein the portion is less than the entire set of information.

7. The method of claim 1, further comprising:

receiving a request to modify a target data structure within a directory;

determining that the directory is governed by the snapshot;

copying a reference to the target data structure from the directory into a directory snapshot data structure, prior to modifying the target data structure;

indicating when the reference was copied into the directory snapshot data structure; and

modifying the target data structure.

8. The method of claim 1, further comprising:

storing in a tracking data structure indications of modified data structures that are governed by the snapshot, wherein the tracking data structure is associated with the snapshot.

9. The method of claim 8, further comprising:

for indications of the modified data structures in the tracking data structure, determining whether data referenced by the modified data structure is associated with data, referenced by older or more recent governing snapshot data structures;

modifying older snapshot data structures based on the data structures in the tracking data structure;

deleting the snapshot associated with the tracking data structure.

10. The method of claim 1, further comprising:

updating data structures in each ancestor of a modified data structure to reflect the snapshots that govern the data structures.

11. The method of claim 10, further comprising:

indicating in the data structures when the data structures have been updated.

12. The method of claim 1, further comprising:

determining which snapshots govern a data structure in response to a request to modify the data structure.

13. A data structure for tracking modifications in a file system comprising:

a first representation of a snapshot that is associated with the data structure; and

a second representation of data structures governed by the snapshot that have been modified.

14. A data structure associated with files or directories in a file system comprising:

an identification field comprised of a first portion and second portion, wherein the first portion is common to versions of the data structure and the second portion is unique to a particular version of the data structure;

a representation of snapshots that govern the data structure; and

a last access field that indicates when the representation was last updated.

15. A system for accessing snapshot data in a file system comprising:

a storage device comprising a file system; and

a processor operably coupled to the storage device configured to;

accept an access request to a path corresponding to a portion of the file system;

determine that the portion of the file system is governed by a snapshot;

identify locations in the storage device that store snapshot data;

retrieve the snapshot data; and

generate an indication that the snapshot data is not the current version of the data.

16. The system of claim 15, wherein a portion of the snapshot data can be accessed as a subdirectory of any ancestor in the at least a portion of the file system.

17. The system of claim 15, wherein the retrieved snapshot data is sent to at least one of:

a client application, a user, an output device, and a remote storage device.

18. A data storage system with per-file snapshot capability comprising:

directory and file nodes forming a data structure tree; and

a software snapshot module configured to allow for preservation of data on a per-file basis as of a given point in time.

19. A data storage system with snapshot capability on a per directory and downstream files basis comprising:

directory and file nodes forming a data structure tree; and

a software snapshot module configured to preserve data stored in all directories and files downstream of the directory which is both closest to the files that include the desired data to be preserved as of a given time and from which directory paths lead down to all said files including the desired snapshot data.

20. A method of preserving data stored in a storage system as of a selected time comprising:

identifying the file within the storage system that includes the desired data to be preserved as of a selected time; and

preserving all the data within said file as of said selected time.

21. The method of claim 20 wherein preserving said identified file as of a selected time is a snapshot and only the data of the identified file is preserved for said snapshot.

22. A method of preserving data stored in a storage system as of a selected time comprising:

identifying the files within the storage system that include the desired data to be preserved as of a selected time;

identifying the directory in the directory/file tree closest to all the identified files and from which paths lead down to the identified files; and

preserving the data in all the files downstream of the identified directory including all downstream files, if any, that were not identified as including data desired to be preserved as of said selected time.