Using shrinkable read-once snapshots for online data backup

• US 20080082593A1
• Filed: 01/09/2007
• Published: 04/03/2008
• Est. Priority Date: 09/28/2006
• Status: Active Grant

• Current Assignee: Paragon Software
• Original Assignee: Paragon Software
• Inventors: Komarov, Konstantin, Usatyuk, Vladamir, Fateev, Oleg, Melkov, Maxim
• Granted Patent: US 7,680,996 B2
• Time in Patent Office: Days
• US Class Current: 707/204
• CPC Class Codes: G06F 11/1451 by selection of backup contents
• 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 2201/84 Using snapshots, i.e. a logical point-in-time copy of the data

Abstract

The present invention discloses a method and system for snapshot-based online backup operations permitting reduced requirements to storage capacity and computational overhead for snapshot function.

At the beginning of an online backup operation, the backup software system creates a snapshot of source data storage. The snapshot includes a watch-list used for identifying blocks of a source storage which are watched by snapshot management means for update. If a block included into the watch-list was requested for update, the snapshot management means preserve original contents of that block in a retention container for the purpose of temporary store. The retention container includes a set of temporal stores dedicated for transient storing of blocks until they are backed up.

The essence of the invention is enabling to exclude blocks from the watch-list and the retention container at any moment within the period of snapshot operation. Therefore it is possible to exclude unnecessary blocks from the scope of blocks managed by the snapshot management means, for the purpose of preserving point-in-time data.

Backed up blocks can be operatively excluded from the snapshot so that unchanged blocks are excluded from the watch-list and updated blocks are removed from the retention container. In the latter case temporal stores are shrunk as well. This technique allows to reduce progressively storage expenses and computational overheads required for maintenance of a snapshot being used in the online backup routine.

When a volume-level online backup is performed the snapshot is switched to the read-once mode at the beginning of the data copying stage. A backup utility performs sequential read of blocks from the snapshot. The snapshot management means automatically exclude requested blocks from the scope of managed blocks.

Claims

1. A method for shrinking a set of data, comprising:

providing a writable volume presented in a computer and used for storing data;

providing a differential snapshot of one or more blocks of said volume, said differential snapshot comprising;

a preservation store for storing copies of the one or more blocks of said volume;

a watch-list structure identifying a first set of blocks of said volume remaining unchanged since a moment of creation of said snapshot;

a retention-list structure identifying updated blocks of said volume and keeping associations of references to said updated blocks with references to original copies of said updated blocks stored in said preservation store;

a space allocation list structure identifying unused space in said preservation store;

providing an input structure specifying a second set of blocks of said volume to be removed from a set of data included to said snapshot;

providing to the computer a set of instructions, the computer operable to execute the instructions to perform;

removing references to the second set of blocks from said watch list,

adding locations referenced by the associations stored in said retention-list which include references to blocks specified by said input structure into said space allocation list;

removing associations stored in said retention-list which include references to blocks specified by said input structure from said retention-list; and

whereby

the number of unchanged blocks included into said snapshot is shrunk.

2. The method of claim 1, further comprising the following steps:

compacting allocation of portions of used space within said preservation store; and

reducing size of said preservation store;

wherein the steps of compacting and reducing are executed after the steps of removing references to the second set of blocks, adding locations and removing associations.

3. A method for performing a snapshot-based online backup with shrinking a set of data included into a snapshot, the method comprising:

providing a writable storage for storing blocks of data;

providing a backup storage for storing data backup;

providing snapshot management means used for controlling a differential snapshot of blocks of said writable storage, said differential snapshot comprising;

a preservation store used for storing a copy of any of said blocks of data;

a watch-list structure identifying blocks of said writable storage remaining unchanged since a moment of creation of said snapshot;

a retention-list structure storing associations of references to updated blocks of said writable storage with references to original copies of updated blocks stored in said preservation store;

a space allocation list structure identifying unused space in said preservation store;

a snapshot shrinking subroutine used for removing block identification data from said watch-list and removing associations data from said retention-list, said subroutine taking a structure specifying blocks a storage as input data, said subroutine comprising instructions for executing the following steps on a computer;

removing references to blocks specified by input data from said watch-list;

adding locations referenced by associations from said retention-list, which include references to blocks specified by input data, into said space allocation list;

removing associations, which include references to blocks specified by input data, from said retention-list;

creating a differential snapshot of said writable storage;

compiling a backup-list of blocks required to back up by analyzing file allocation on said snapshot; and

performing a backup of portions of blocks included into said backup-list until said backup-list becomes empty, the step of performing a backup comprising

by iteratively executing at least the following steps;

reading a portion of blocks from said snapshot into a memory buffer for further processing and storing on said backup storage;

invoking said snapshot shrinking routine with specifying a structure identifying locations of blocks included into said portion as input data;

removing references to blocks included into said portion from said backup list.

4. The method of claim 3, further comprising the following steps of:

compiling a map of surplus blocks not needed to back up, by analyzing file allocation on said snapshot;

invoking said snapshot shrinking routine with specifying said map of surplus blocks as input data;

wherein the step of compiling a map is executed after the step of creating a differential snapshot and before the step invoking said snapshot; and

wherein the step of invoking said snapshot is performed before the step of compiling a backup-list.

5. The method of claim 4, wherein the step of creating a differential snapshot comprises the steps of

suspending I/O write activity on said writable storage;

bringing a file system on said writable storage into consistent state;

starting copy-on-write technique for preserving point-in-time data on said volume;

resuming I/O write activity on said writable storage;

enabling access to point-in-time data stored on said snapshot;

computing a map of unused blocks in a file system located on said snapshot; and

invoking said snapshot shrinking subroutine with specifying said map of unused blocks as input data.

6. A backup system for performing a snapshot-based online backup, the system comprising:

a writable storage for storing blocks of data;

a backup storage for storing data backup;

a computer system controlling said writable storage device and said backup storage, said the computer system comprising;

snapshot management means for controlling a differential snapshot of data blocks of said writable storage system, said differential snapshot comprising;

a preservation store used for storing a copy of any of said blocks of data;

a watch-list structure identifying blocks of said writable storage remaining unchanged since a moment of creation of said snapshot;

a retention-list structure storing associations of references to updated blocks of said writable storage with references to original copies of updated blocks stored in said preservation store,

a space allocation list structure identifying unused space in said preservation store;

means for enabling access to data stored on a snapshot;

means for shrinking a set of data included to said snapshot, the means for shrinking operable to perform the steps of;

removing references to specified blocks from said watch-list;

adding locations referenced by associations stored in said retention-list which include references to said specified blocks into said space allocation list; and

removing associations stored in said retention-list which include references to said specified blocks;

means for performing a snapshot-based online backup with shrinking a set of data included to a snapshot during backup operation, the means for performing a snapshot-based online backup operable, in an interactive manner, to;

read a portion of blocks from said snapshot into a memory buffer for further processing and storing on said backup store;

invoke said means for shrinking a set of data included to a snapshot with specifying locations of blocks from portion of blocks as input data.

7. The backup system of claim 6, wherein said preservation store is stored on the writable storage.

8. A The backup system of claim 6, wherein said preservation store is stored on the writable storage.

9. The backup system of claim 6, wherein said preservation store is a separate partition of the writable storage.

10. The backup system of claim 6, wherein said preservation store is a file within a file system on the writable storage.

11. The backup system of claim 6, wherein backed up data blocks are restored on-the-fly to a different storage.