Error detection/correction and fault detection/recovery – Data processing system error or fault handling – Reliability and availability
Reexamination Certificate
2000-10-06
2004-05-04
Beausoliel, Robert (Department: 2184)
Error detection/correction and fault detection/recovery
Data processing system error or fault handling
Reliability and availability
C714S021000, C711S161000, C711S162000, C707S793000
Reexamination Certificate
active
06732293
ABSTRACT:
COPYRIGHT NOTICE/PERMISSION
A portion of the disclosure of this patent document contains material that is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever. The following notice applies to the software and data as described below and in the drawing hereto: Copyright 0 1999, Wild File, Inc. All Rights Reserved.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to the storage of digital data, and more particularly to method and apparatus for tracking changes made by an operating system (OS) for the files under its management within the context of a change tracking system that supports the backup and recovery of data stored by a digital computer
2. Description of the Related Art
Applications executing on computers typically operate under an operating system (OS) that has the responsibility, among other things, to save and recall information from a hard disk. The information is typically organized in files. The OS maintains a method of mapping between a file and the associated locations on a hard disk at which the file's information is kept.
Currently computers are generally operated in a manner where information (data) is read and written to a disk for permanent storage. Periodically a backup (copy) is typically made of the disk to address two types of problems: First, the disk itself physically fails making the information it had contained inaccessible. Second, if the information on disk changes and it is determined the original state was desired, a user uses the backup to recover this original state. Backups can be made to the same disk or to an alternate media (disk, tape drive, etc.).
Tape backup traditionally involves duplicating a disk's contents, either organized as files or a disk sector image, onto a magnetic tape. Such a tape is typically removable and therefore can be stored off-site to provide recovery due to a disk drive malfunction or even to an entire site (including the disk drive) being destroyed, for example, in a fire.
When information is copied from a disk to tape in the form of a sector level disk image (i.e., the information is organized on the tape in the same manner as on the disk), a restoration works most efficiently to an identical disk drive. The reason for such an organization is speed. Reading the disk sequentially from start to end is much faster than jumping around on the disk reading each file one at a time. This is because often a file is not stored continuously in one area of the disk, but may be spread out and intermixed with other files across the entire disk. When information is copied one file at a time to a tape it is possible to efficiently restore one or more files to a disk that may be both different and already containing data.
Tape backup focuses on backing up an entire disk or specific files at a given moment in time. Typically the process will take a long time and is thus done infrequently, such as during the evening. Incremental backups involve only saving data that has changed since the last backup, thus reducing the amount of tape and backup time required. However, a full system recovery requires that the initial full system backup and all subsequent incremental backups be read and combined in order to restore to the time of the last incremental backup. One key shortcoming of tape backup is that if a recent backup is not performed the information and work generated after the last backup may be lost.
Write-once optical disk backup as performed by a WORM drive has many of the same qualities as tape backup. However, because of the technology involved, it is not possible to overwrite data. Therefore it provides some measure of a legal “accounting” system for unalterable backups. WORM drives cannot provide continuous backup of changing disk information because eventually they will fill.
A RAID system is a collection of drives which collectively act as a single storage system, which can tolerate the failure of a drive without losing data, and which can operate independently of each other. The two key techniques involved in RAID are striping and mirroring. Striping has data split across drives, resulting in higher data throughput. Mirroring provides redundancy by duplicating all data from one drive on another drive. Generally, data is not lost if only one drive fails, since the other has another copy.
RAID systems are concerned with speed and data redundancy as a form of backup against physical drive failures. However, RAID systems do not address reverting back in time to retrieve information that has since changed;
The Tilios Operating System was developed several years ago, and provided for securing a disk's state and then allowing the user to continue on and modify it. The operating system maintained both the secured and current states. Logging of keystrokes was performed so that in the event of a crash, where the current state is lost or becomes invalid, the disk could easily revert to its secured state and the log replayed. This would recover all disk information up to the time of the crash by, for example, simulating a user editing a file. The secured disk image was always available along with the current so that information could be copied forward in time-i.e., information saved at the time of the securing backup could be copied to the current state.
The Tilios Operating System could perform a more rapid backup because all the work was performed on the disk (e.g., there was no transfer to tape) and techniques were used to take advantage of the incremental nature of change (i.e., the current and secured states typically only had minor differences). Nonetheless, the user was still faced with selecting specific times at which to secure (backup) and the replay method for keystrokes was not entirely reliable for recreating states subsequent to the backup. For example, the keystrokes may have been commands copying data from a floppy disk or the Internet, both of whose interactions are beyond the scope of the CPU and disk to recreate.
Simply creating a backup a file by making a copy of a file under a new name, typically changing only a file's extension (e.g., “abc.doc” is copied to “abc.bak”) has been a long standing practice. In the event the main file (abc.doc) is corrupted or lost, one can restore from the backup (abc.bak). This process is much the same as doing a selective tape backup and carries the issues of managing the backups (when to make, when to discard, etc.).
In summary, a RAID system only deals with backup in the context of physical drive failures. Tape, WORM, Tilios, and file copies also address backup in the context of recovering changed (lost) information.
The traditional backup process involves stopping at a specific time and making a duplicate copy of the disk's information. This involves looking at the entire disk and making a copy such that the entire disk can be recreated or specific information recalled. This process typically involves writing to a tape. Alternatively, a user may backup a specific set of files by creating duplicates that represent frozen copies from a specific time. It is assumed the originals will go on to be altered. This process typically involves creating a backup file on the same disk drive with the original. Note that a “disk” may actually be one or more disk drives or devices acting in the manner of a disk drive.
In both of these cases the user must make a conscious decision to make a backup. In the second case a specific application, like a text editor, may keep the last few versions of a file (information). However, this can lead to wasted disk space as ultimately everything is duplicated long after files have stabilized. In other words, while working on a document a user may likely want to revert to a prior version, but once finished and years later, it is very unlikely the user would c
Beausoliel Robert
Fenwick & West LLP
Puente Emerson
Symantec Corporation
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