Apparatus and Method for Hardware-Based File System

• US 20080040385A1
• Filed: 08/20/2007
• Published: 02/14/2008
• Est. Priority Date: 11/01/2002
• Status: Active Grant

• Current Assignee: Hitachi Vantara, LLC (Hitachi, Ltd.)
• Original Assignee: Bluearc UK Ltd. (Hitachi, Ltd.)
• Inventors: Willis, Trevor, Aston, Christopher, Barrall, Geoffrey, Benham, Simon
• Granted Patent: US 8,224,877 B2
• Time in Patent Office: Days
• US Class Current: 707/103Y
• CPC Class Codes: G06F 12/0246 in block erasable memory, e.g. flash memory
• 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 16/183 Provision of network file services by network file servers, e.g. by using NFS, CIFS network file access protocols H04L67/1097
• CPC Class Codes: G06F 16/1873 Versioning file systems, temporal file systems, e.g. file system supporting different historic versions of files
• CPC Class Codes: Y10S 707/99945 Object-oriented database structure processing
• CPC Class Codes: Y10S 707/99948 Application of database or data structure, e.g. distributed, multimedia, or image

Abstract

A hardware-based file system includes multiple linked sub-modules that perform functions ancillary to client data handling. Each sub-module is associated with a metadata cache. A doubly-rooted structure is used to store each file system object at successive checkpoints. Metadata is stored within an object and/or as a separate object. Provisions are made for allocating sparse objects. A delayed write feature is used for writing certain objects into non-volatile storage. Checkpoints can be retained as read-only versions of the file system. Modifications to the file system are accomplished without affecting the contents of retained checkpoints. The file system can be reverted to a retained checkpoint. Multiple file servers can be interconnected as a cluster, and each file server stores requests from another file server. Interconnections between file servers can be dynamically modified. A distributed locking mechanism is used to control access to file system objects stored by the file servers.

Claims

1. A method for maintaining a file system object in a non-volatile storage at successive checkpoints, the method comprising:

maintaining an object structure for the file system object, the object structure comprising a first tree structure rooted by a first root node and a second tree structure rooted by a second root node, each tree structure optionally including a number of intermediate nodes and a number of data blocks, each tree structure representing a version of the file system object; and

alternately managing the object structure using the first tree structure rooted by the first root node while storing the second tree structure rooted by the second root node in the non-volatile storage and managing the object structure using the second tree structure rooted by the second root node while storing the first tree structure rooted by the first root node in the non-volatile storage.

2. The method of claim 1, further comprising:

maintaining a version number for each root node, the version number indicating the checkpoint associated with the corresponding tree structure.

3. The method of claim 1, wherein the non-volatile storage comprises a plurality of sectors, and wherein the first and second root nodes are stored in adjacent sectors in the non-volatile storage.

4. The method of claim 2, further comprising:

determining a latest valid version of the file system object based upon the version numbers of the root nodes.

5. The method of claim 1, further comprising:

maintaining a list of free space areas of the non-volatile storage;

maintaining a list of free root nodes;

allocating the root nodes for the object structure from one of the list of free space areas and the list of free root nodes; and

allocating intermediate nodes and data blocks for the object structure only from the list of free space areas.

6. The method of claim 5, further comprising:

deleting the file system object from the non-volatile storage.

7. The method of claim 6, wherein deleting the file system object from the non-volatile storage comprises:

adding the root nodes to the list of free root nodes; and

adding the intermediate nodes and data blocks to the list of free space areas.

8. A method for storing metadata associated with an object in a file system, the method comprising:

maintaining a first object structure for the object, the object structure including at least a root node and optionally including intermediate nodes and data blocks; and

storing a first portion of metadata in the root node.

9. The method of claim 8, further comprising:

allocating a number of data blocks for storing a second portion of metadata.

10. The method of claim 9, further comprising:

allocating a second object structure for storing a third portion of metadata.

11. The method of claim 10, further comprising:

storing a reference to the second object structure within the first object structure.

12. The method of claim 11, wherein storing a reference to the second object structure within the first object structure comprises:

storing the reference in the root node of the first object structure.

13. The method of claim 11, wherein storing a reference to the second object structure within the first object structure comprises:

storing the reference within the second portion of metadata.

14. An apparatus comprising:

a non-volatile storage; and

means for maintaining a file system object in the non-volatile storage at successive checkpoints using an object structure having two and only two root nodes for managing a current version of the object, said means alternating between the two root nodes for managing the object at the successive checkpoints.

15. The apparatus of claim 14, further comprising:

means for retaining read-only versions of the object through the object structure.

16. The apparatus of claim 15, further comprising:

means for deleting a retained read-only version of the object from the object structure.

17. The apparatus of claim 15, further comprising:

means for deleting the current version of the object while at least one retained read-only version of the object exists in the object structure.

18. The apparatus of claim 15, further comprising:

means for reverting the current version of the object to a retained read-only version of the object.