# Patent

## Title
Snapshot indexing

## Abstract

Managing backup data comprises mounting a snapshot of a file system. Each of the plurality of snapshots is taken at a particular time and each comprises a replica of the data set at that particular time. The mounted snapshot is accessed. For each of the one or more file system objects included in the accessed snapshot, index data is added which indicates that each of the one or more file system objects is located within the accessed snapshot. This information is added to an index associated with the snapshot so that it is able to be determined, using the index and without having to again mount the accessed snapshot, whether an object of interest is included in the snapshot.

## Background
CROSS REFERENCE TO OTHER APPLICATIONS
This application is a continuation of co-pending U.S. Patent Application Ser. No. 11/207,588, entitled SNAPSHOT INDEXING filed Aug. 18, 2005 which is incorporated herein by reference for all purposes.


BACKGROUND OF THE INVENTION
Reliable data backup is an important requirement of computer systems today. Traditional backup systems typically perform backup by copying file systems onto data storage media such as tapes or optical disks. For file systems containing large amounts of data, the copying process often takes a long time. Therefore, traditionally backups have been performed relatively infrequently, such as on daily or weekly basis. More recently, “snapshot” type backup systems and/or programs have been provided, which are capable of storing backup data more frequently, in some cases as often as a user requests. However, traditionally to use backup data to restore a particular file or other stored object, e.g., a particular prior version of a file, a user has had to undergo lengthy restore operations. Each backup data set in which the file might be included would be used to “restore” the source data set to a state associated with the backup data, and then the file system of the restored data set traversed to search for the desired file. This restore and browse approach can consume excessive time and resources, particularly with backup data being generated more and more frequently, as “snapshot” and related technologies permit. It would be useful, therefore, to have a way to enable users to more quickly and easily access specific files and other objects from backup data.



BRIEF DESCRIPTION OF THE DRAWINGS
Various embodiments of the invention are disclosed in the following detailed description and the accompanying drawings.
FIG. 1 is a block diagram illustrating an embodiment of a backup system.
FIG. 2 is a flowchart illustrating an embodiment of a process for managing backup data.
FIG. 3 is a flowchart illustrating an embodiment of a backup data management process.
FIG. 4A is a diagram illustrating the layout of an index entry according to some embodiments.
FIG. 4B illustrates the details of the header, version and children sections of an index entry example as implemented in some embodiments.
FIG. 5 is a flowchart illustrating an embodiment of a process for using the snapshot index to recover previously stored data.
FIG. 6 is a flowchart illustrating an embodiment of a process for browsing backup data.
FIG. 7 is a diagram illustrating an example of a user interface for browsing.
FIG. 8 is a flowchart illustrating an embodiment of a process for searching backup data.
FIG. 9 is a diagram illustrating an embodiment of a user interface for searching backup data.
FIG. 10 is a diagram illustrating an embodiment of a user interface for searching backup data.



DETAILED DESCRIPTION
The invention can be implemented in numerous ways, including as a process, an apparatus, a system, a composition of matter, a computer readable medium such as a computer readable storage medium or a computer network wherein program instructions are sent over optical or electronic communication links. In this specification, these implementations, or any other form that the invention may take, may be referred to as techniques. A component such as a processor or a memory described as being configured to perform a task includes both a general component that is temporarily configured to perform the task at a given time or a specific component that is manufactured to perform the task. In general, the order of the steps of disclosed processes may be altered within the scope of the invention.
A detailed description of one or more embodiments of the invention is provided below along with accompanying figures that illustrate the principles of the invention. The invention is described in connection with such embodiments, but the invention is not limited to any embodiment. The scope of the invention is limited only by the claims and the invention encompasses numerous alternatives, modifications and equivalents. Numerous specific details are set forth in the following description in order to provide a thorough understanding of the invention. These details are provided for the purpose of example and the invention may be practiced according to the claims without some or all of these specific details. For the purpose of clarity, technical material that is known in the technical fields related to the invention has not been described in detail so that the invention is not unnecessarily obscured.
Managing data backup is disclosed. In some embodiments, snapshots of a data set are taken at various times. The data set includes one or more objects. Information about the objects is stored in an index database. In some embodiments, the index database includes for each object in the data set an index entry that includes information indicating for each version of the object stored in connection with a snapshot a location of the version within the snapshot data. The snapshot may be stored locally or remotely. The index database allows the user to browse or search for entries of interest. Relevant entries or versions of entries can be retrieved from the snapshot data and presented to the user.
FIG. 1 is a block diagram illustrating an embodiment of a backup system. In this example, backup client 100 includes data subject to backup operations. Backup client 100 can be implemented as computer code, a hardware device, a software/hardware combination or any other appropriate system or system components. Applicable data for the backup operations includes various types of systematically organized data sets comprised of files, directories, databases, or other appropriate data objects. Replicas of the data sets are taken at different times and stored as backups. As used herein, a replica of the data set is also referred to as a snapshot.
In the example shown, the data set to be backed up is a file system 102, which includes a systematically organized collection of files and directories. For purposes of clarity, the following examples only refer to file objects and directory objects, although other types of objects such as database objects can also be used.
Multiple snapshots 104 of the file system are taken at different times. Various techniques for taking snapshots are employed in different system implementations. For example, in some systems, a special purpose device driver duplicates file system data on multiple disks as the data is created or modified. When the system issues a command to take a snapshot, the data on a designated disk is preserved and serves as a snapshot of the file system for backup purposes. Multiple snapshots may be created for a file system. The maximum number of snapshots depends on the implementation of the backup system. Different snapshots may be identified using version numbers, time stamp, or other appropriate identification techniques. In some embodiments, to make room for new snapshots, older snapshots may be set to expire or overwritten. In some embodiments, an application running on client 100 and/or another host generates and stores the snapshots 104.
In the example shown, an indexing service 106 manages an index 108. The index is a database that includes information about data objects in the snapshots. It can be used for browsing, searching or otherwise retrieving specific data objects stored in the snapshots. As will be shown in more details below, the index service is configured to update the entries in index 108 based on the snapshots.
In this example, snapshots 104 are shown to be local to the backup client. In other words, backup client 100 can access the snapshot without requiring data transfer on a network. In some systems, the snapshots may be stored remotely, such as on a networked storage device, a server or the like. Similarly, indexing service 106 and index 108 may also be located locally or remotely with respect to the backup client.
FIG. 2 is a flowchart illustrating an embodiment of a process for managing backup data. Process 200 is implemented as a part of indexing service 106 in some embodiments. The process is configured to manage the snapshot index and may operate on a backup client or other appropriate remote device. In the example shown, the process begins when a snapshot becomes available (202). The snapshot is accessed (204). Data associated with an object comprising the snapshot is added to an index (206). In some embodiments, an index entry that corresponds to an object in the snapshot is updated to indicate the relative location of the object within the snapshot. In some embodiments, data is added to the index for each object comprising the snapshot.
FIG. 3 is a flowchart illustrating an embodiment of a backup data management process. In this example, process 300 is performed sometime after the snapshot is created. The indexing service receives an indication that a new snapshot is available (302). The snapshot is accessed (304). In some embodiments, accessing the snapshot includes mounting the snapshot to enable the snapshot data to be accessed by navigating a corresponding file system. The file system is then traversed to locate each file system object such as files or directories (306). In some embodiments, the file system is traversed without requiring that the snapshot be mounted.
During the traversal, the index entry for each file system object is updated (308-311). It is determined whether the object is new (308). A file system object is new if, for example, it has no corresponding index entry in the index. If the file system object is new, a new index entry for the new file system object is generated and added to the index (309). If, however, the file system object is not new (i.e., it has an existing index entry), then information about the file system object in the current snapshot is added to the existing, corresponding entry (310). The entry update process (308-310) is repeated until all file system objects have been traversed (311). When the traversal is complete and the index entries have been updated, the index is saved (312). The file system is then un-mounted and cleaned up (314). When another new snapshot becomes available, the process repeats and the index entries are updated based on the file system objects in the new snapshot. In this example, if the same object appears in more than one snapshot, a single index entry associated with the object is updated each time the object is encountered in a snapshot, e.g., by adding to the entry data indicate the presence and/or location of the object, and/or a version thereof, within the snapshot. In some embodiments, a separate entry is made for each instance of an object encountered in a snapshot.
In some embodiments, the index is a database that includes multiple index entries. FIG. 4A is a diagram illustrating the layout of an index entry according to some embodiments. In this example, the database is implemented in a table format with a fixed length entry. Each entry is referenced and located using its position in the table. In other words, the identifier of each entry corresponds to its entry number in the table, and an entry can be accessed if its identifier (or its offset in the table) is known. During a search operation, the table is searched linearly to locate one or more matching entries. In some embodiments, the media in which the index is stored supports faster linear access than random access, thus linear search requiring linear access is faster than hierarchical search requiring random access.
Each of the index entries has the layout shown in 400 and each corresponds to a file system object. The index entry includes information useful for accessing the file system object and its parent or children in the snapshots. As shown, an index entry includes three sections: a header section for storing general information about the file system object (e.g. file name or object name), a version section for storing information about different versions of the object, e.g., as found in different snapshots, and a children section for storing information about the object's children.
In some embodiments, the object's children include objects, such as file system objects (e.g., files and directories), if any, that occur in a next level below the parent object in a hierarchical structure with which the parent object is associated, e.g., a file system directory or structure associated with the snapshot in which the object is included and/or a source data set with which the snapshot is associated. In some embodiments, capturing in the index entry of FIG. 4A data identifying an object's parent (e.g., in the header) and/or children, if any, enables a hierarchical representation of the data to be presented, e.g., by providing a file system or directory type interface that enables a user to browse a hierarchical structure to find a particular object of interest, if desired.
FIG. 4B illustrates the details of the header, version and children sections of an index entry example as implemented in some embodiments. The example entry has an identifier that corresponds to its position in the table. Table 402 shows the layout of the header section, which includes fields for storing general information about the index entry, such as the offsets and lengths of the object's name, version table and child table information, identifier of the entry's parent directory, etc. In case that the fields of this entry are filled up, further information about the entry is stored in a continuation entry, whose identifier is included in the header.
The version section of this example includes one or more version entries corresponding to one or more versions of snapshots. The snapshots are stored in a snapshot table. Table 404 shows the layout of one version entry, which includes an identifier that identifies the snapshot table entry that is associated with the snapshot within which the version with which the version entry is associated resides, the size of the version of the file in the snapshot, and the time this version of the object was last modified.
Each children section in this example includes one or more child entries. Table 406 shows the layout of one child entry, which includes the identifier of the index entry that represents the child.
Although FIGS. 4A-4B illustrate the layout of an index that is a flat file with fixed length entries, variable length entries, entries with different fields and different layout are sometimes used in other embodiments as appropriate.
A user may wish to access the snapshots and recover data from them, such as a previous version of a file or other object. FIG. 5 is a flowchart illustrating an embodiment of a process for using the snapshot index to recover previously stored data. Process 500 is implemented as a part of the indexing service in some embodiments. In some embodiments, the process is implemented separately and is capable of cooperating with the indexing service. In the example shown, process 500 begins when a request is received (502). As will be shown in more details below, such a request includes browsing or searching the snapshots. Responsive data associated with the request is located in an index (504). In this example, the index is a snapshot index that includes entries that identify one or more objects comprising one or more snapshots of a data set and the responsive data includes an appropriate index entry in the snapshot index that corresponds to the request. Information associated with the object with which the responsive data is associated, such as information about the object's snapshots, is provided to the caller routine that made the request (506).
FIG. 6 is a flowchart illustrating an embodiment of a process for browsing backup data. In this example, information in the snapshot index is represented to the user via a user interface, allowing the user to browse the snapshots. Process 600 initiates when a browse request is received (602). In the example shown, the browse request is received when a user makes a browse request via the user interface. The index entry representing the root of the file system (or other hierarchical structure, in the case of a source data set other than a file system) is then located and the child entries are retrieved (604). In some embodiments, the root of the file system occupies a fixed location in the index (e.g. the second entry in the index).
The user may continue to browse by making a selection in the user interface. Once a user selection is made and received, the type of selection is determined (606). In this case, the user may select a directory object or a file object. If a file object is selected, index data corresponding to the selected file object is accessed and retrieved (608). The index data includes information about different versions of snapshots, which is displayed to the user in the user interface. The user has the option to request via the user interface that a particular instance of an object be retrieved, e.g., from data associated with the snapshot with which the instance of the object is associated. The process enters into a state of waiting for the user to make a request. If such a request is made (609), the requested instance of the object, e.g., a particular version, is retrieved and made available to the user (610). If the user does not make such a request, the process continues to wait until the user indicates that he has finished with browsing (614).
If the user selected a directory (606), the child entries of the selected directory are retrieved and optionally displayed to the user (612). The user again has the option of selecting from the children a directory or a file (608). Thus, the process of retrieving either the children of the selected directory (614) or file-related index data/snapshot (608-610) is repeated. The user may close the window, click on a “clear” button provided in the user interface or otherwise indicate that he has finished browsing; or, he may continue to browse (614).
FIG. 7 is a diagram illustrating an example of a user interface for browsing. User interface 700 shown in this example gives the user the option to select the number of snapshots to be presented in the user interface. The user may browse a particular snapshot by making a selection. A “clear” button is provided to allow the user to clear his selection and start over.
FIG. 8 is a flowchart illustrating an embodiment of a process for searching backup data. In this example, process 800 initiates in a state of waiting for a search request from a user (802). The request includes query information such as a search string used for file name matching, the number of versions to be searched, etc. When a search request is received, the process compares the search string with the file names in the index entries to locate one or more potential matches (804). In some embodiments, the search examines all the entries to find all potential matches. Information associated with the potential matches (e.g., version information of the snapshots) is retrieved and optionally displayed to the user (806). The process then enters into a state of waiting for user input (808). Once a user input is received, its type is determined (810). If the user input is one which selects an instance of an object from the matching entries, the requested instance is retrieved and optionally displayed to the user (812). If the user input is one which clears the search results, the process returns to the initial state to wait for a new search request input (802). If the user input indicates that the user is done with searches, the process ends (814).
FIG. 9 is a diagram illustrating an embodiment of a user interface for searching backup data. User interface 900 shown in this example gives the user the option of choosing the number of backups used in the search. The user selects the number of backups searched via menu 904. The search string is entered in box 902. Matching entries from the last three backups (in the example shown, because the user has selected “last 3 backups” via menu 904) are displayed in area 906. The user can view, save or otherwise recover an instance of a file by clicking on the desired file name. For example, a file such as “Expense Report June.xls” which existed in some snapshots but became deleted in later snapshots can be found and retrieved. The user can clear the search result by pressing button 908 or close the search window by pressing button 910.
FIG. 10 is a diagram illustrating an embodiment of a user interface for searching backup data. User interface 1000 shown in this example gives the user the option of finding, from among all files stored in the backup data for which an index is available, all files that match the search string entered by the user. The search results are displayed in area 1002, where version information associated with each matching file is displayed and selectable.
Managing data backup has been disclosed. The techniques described allow the user to access backup data without having to mount and navigate the file system (or other hierarchical structure) of each snapshot or other backup data set in which an object of interest may reside. The location within backup data of an object of interest, such as a particular version of a file of interest, can be determined and, if desired, the object can be retrieved and provided to the user quickly and easily.
Although the foregoing embodiments have been described in some detail for purposes of clarity of understanding, the invention is not limited to the details provided. There are many alternative ways of implementing the invention. The disclosed embodiments are illustrative and not restrictive.

## Claims

1. A method of managing backup data, comprising:
mounting a snapshot of a file system, each of the plurality of snapshots being taken at a particular time and each comprising a replica of the data set at that particular time;
using a processor to access the mounted snapshot; and using the processor to add, for each of the one or more file system objects included in the accessed snapshot, index data indicating that each of the one or more file system objects is located within the accessed snapshot to an index associated with the snapshot in order to be able to determine, using the index and without having to again mount the accessed snapshot, whether an object of interest is included in the snapshot, wherein:
each file system object in a file system has its own corresponding index entry; and adding to the index includes:
encountering a file system object in the mounted snapshot;
determining whether an index entry corresponding to the encountered file system object already exists;
in the event the determination determines that an index entry corresponding to the encountered file system object already exists, adding information associated with the encountered file system object to the already-existing index; and
in the event the determination determines that an index entry corresponding to the encountered file system object does not already exist:
creating a new index entry that corresponds to the encountered file system object; and
adding information associated with the encountered file system object to the created index.

2. The method of claim 1, wherein an index entry includes a header section that includes a name of the file system object, a version section that includes information associated with one or more versions of the file system object, and a children section that includes information associated with the file system object's children, if any.

3. The method of claim 1 further comprising:
receiving a browse request that includes a number of last snapshots to display; and
displaying the requested last snapshots, including a backup date and/or time for each of the requested last snapshots.

4. The method of claim 1 further comprising:
receiving a search request that includes a search string;
comparing the search string against one or more file names in the index; and
displaying a match resulting from the comparison, including by displaying a backup date and/or time for each matching file.

5. The method of claim 4 further comprising receiving a number of matching files to display, wherein the number of matches displayed is limited to the received number.

6. The method of claim 4, wherein a plurality of matching files are displayed and the method further includes:
receiving a selection of one of the plurality of matching files displayed; and
restoring, in response to the received selection, the selected file.

7. A system for managing backup data, comprising:
a processor configured to:
mount a snapshot of a file system, each of the plurality of snapshots being taken at a particular time and each comprising a replica of the data set at that particular time;
access the mounted snapshot; and
add, for each of the one or more file system objects included in the accessed snapshot, index data indicating that each of the one or more file system objects is located within the accessed snapshot to an index associated with the snapshot in order to be able to determine , using the index and without having to again mount the accessed snapshot, whether an object of interest is included in the snapshot, wherein:
each file system object in a file system has its own corresponding index entry; and the processor is configured to add to the index by:
encountering a file system object in the mounted snapshot;
determining whether an index entry corresponding to the encountered file system object already exists;
in the event the determination determines that an index entry corresponding to the encountered file system object already exists, adding information associated with the encountered file system object to the already-existing index; and
in the event the determination determines that an index entry corresponding to the encountered file system object does not already exist:
creating a new index entry that corresponds to me encountered file system object; and adding information associated with the encountered file system object to the created index; and
a memory coupled to the processor, configured to provide the processor with instructions.

8. The system of claim 7, wherein the processor is further configured to:
receive a browse request that includes a number of last snapshots to display; and
display the requested last snapshots, including a backup date and/or time for each of the requested last snapshots.

9. The system of claim 7, wherein the processor is further configured to:
receiving a search request that includes a search string;
comparing the search string against one or more file names in the index; and
displaying a match resulting from the comparison, including by displaying a backup date and/or time for each matching file.

10. The system of claim 9, wherein the processor is further configured to receive a number of matching files to display, wherein the number of matches displayed is limited to the received number.

11. The system of claim 9, wherein a plurality of matching files are displayed and the processor is further configured to:
receive a selection of one of the plurality of matching files displayed; and
restore, in response to the received selection, the selected file.

12. The system of claim 7, wherein an index entry includes a header section that includes a name of the file system object, a version section that includes information associated with one or more versions of the file system object, and a children section that includes information associated with the file system object's children, if any.

13. A computer program product for managing backup data, the computer program product being embodied in a computer readable storage medium and comprising computer instructions for:
mounting a snapshot of a file system, each of the plurality of snapshots being taken at a particular time and each comprising a replica of the data set at that particular time;
accessing the mounted snapshot; and
adding, for each of the one or more file system objects included in the accessed snapshot, index data indicating that each of the one or more file system objects is located within the accessed snapshot to an index associated with the snapshot in order to be able to determine , using the index and without having to again mount the accessed snapshot, whether an object of interest is included in the snapshot, wherein:
each file system object in a file system has its own corresponding index entry; and adding to the index includes:
encountering a file system object in the mounted snapshot;
determining whether an index entry corresponding to the encountered file system object already exists;
in the event the determination determines that an index entry corresponding to the encountered file system object already exists, adding information associated with the encountered file system object to the already-existing index; and
in the event the determination determines that an index entry corresponding to the encountered file system object does not already exist:
creating a new index entry that corresponds to the encountered file system object; and adding information associated with the encountered file system object to the created index.

14. The computer program product of claim 13 further comprising computer instructions for:
receiving a browse request that includes a number of last snapshots to display; and
displaying the requested last snapshots, including a backup date and/or time for each of the requested last snapshots.

15. The computer program product of claim 13 further comprising computer instructions for:
receiving a search request that includes a search string;
comparing the search string against one or more file names in the index; and
displaying a match resulting from the comparison, including by displaying a backup date and/or time for each matching file.

16. The computer program product of claim 15 further comprising computer instructions for receiving a number of matching files to display, wherein the number of matches displayed is limited to the received number.

17. The computer program product of claim 15, wherein a plurality of matching files are displayed and the computer program product further includes computer instructions for:
receiving a selection of one of the plurality of matching files displayed; and
restoring, in response to the received selection, the selected file.

18. The computer program product of claim 13, wherein an index entry includes a header section that includes a name of the file system object, a version section that includes information associated with one or more versions of the file system object, and a children section that includes information associated with the file system object's children, if any.