Electrical computers and digital processing systems: memory – Storage accessing and control – Control technique
Reexamination Certificate
1999-06-10
2003-04-01
Kim, Matthew (Department: 2186)
Electrical computers and digital processing systems: memory
Storage accessing and control
Control technique
C711S156000, C711S112000, C711S173000
Reexamination Certificate
active
06542975
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to disk drive backup systems and, more particularly, to image backup methods for backing up data from disk partitions of storage devices.
2. Description of the Related Art
Modern computer systems typically include one or more mass storage devices such as hard disk drives, optical disc drives, floppy disk drives, removable disk drives, and the like to store a large amount of information. Often, however, the storage devices fail to operate properly for various electromechanical defects. In the event of such failures, valuable data stored on the storage devices may be lost permanently or may require costly and time consuming repairs to recover the original data.
To guard against such failures, modern computer systems typically employ a backup system to backup data stored on a storage device.
FIG. 1
illustrates an exemplary computer system
100
including a host computer
102
and a backup device
104
. The backup device
104
is coupled to the host computer
102
by means of a bus
106
for backing up the contents of one or more storage devices (e.g., hard disk drives, optical drives, etc.) in the host computer
102
. The backup device
104
then provides the backed up data to the host computer
102
to restore the original data when necessary. For example, data may be restored from the backup device when a backed up hard drive fails or when data on a backed up hard drive become corrupted.
The storage devices such as fixed disk drives (e.g., hard disk drives, removable disk drives, etc.) generally include one or more disks for storing data. For example, conventional hard disk drives include one or more disks that are partitioned into one or more partitions (e.g., volumes, logical drives, etc.), which is well known in the art. Each of the disk partitions is a logically self-contained volume and is typically represented by a drive letter such as “C,” “D,” “E,” or the like. In addition, each partition contains files and directory bit maps such as file allocation table or the like. Typically, a partition is organized as a linear sequence of clusters, each of which is comprised of a number (i.e., set) of sectors.
FIG. 2A
illustrates a schematic diagram of an exemplary disk
200
for storing data. The disk
200
is configured to include a plurality of tracks
202
. Each of the tracks
202
is divided into sectors
204
for storing data. The disk
200
may be partitioned into one or more partitions with each partition having a file allocation data structure such as a file allocation table.
As is well known in the art, the partitions of a disk are generally organized in sectors.
FIG. 2B
shows a schematic diagram of an exemplary track
202
divided into sectors
204
. A sector may be any size, but is typically 512 bytes in size. In this arrangement, files are configured to be stored in the disk
200
in units of clusters
206
. Each of the clusters
206
includes a pair of sectors
204
. As is well known in the art, however, a cluster may include any number of number of contiguous sectors typically in powers of two (e.g., 1, 2, 4, 8, 16, etc.).
In general, data in a storage device are backed up using one of two techniques: file-based backup and image-based backup. In the file-based backup method, the contents of individual files are copied from a source disk onto a backup media. The files are usually copied without regard for how they are arranged on the source disk. For example, a partition may have ten sectors containing two files. One file is stored in sectors two through four and sectors eight and nine while the other file is stored in sectors five through seven. The remaining sectors zero and one are unused. In this case, the file-based backup would store information in the backup in the following sequence: sectors two through four, eight and nine, five through seven, such that the unused sectors zero and one are not copied.
The file-based backup method, however, may require a substantial number of non-sequential read and write operations to back up an entire partition since a partition often contains hundreds or even thousands of files. For example, to back up the former file in sectors two through four and sectors eight and nine, a backup system reads sectors two through four first, and then performs a seek to sector eight for reading sectors eight and nine. Such non-sequential read and write operations entail numerous seek operations to proper sectors of clusters.
In contrast, the image-based backup method generally reduces the time required to backup an entire partition. Image-based backup systems are capable of backing up one or more partitions in a disk. In this method, all data on the partition, including valid data, free space, and invalid data, are copied and stored on a backup medium. For example, to perform an image backup of a partition “C,” the image-based backup method operates to read and store the data on the partition sequentially from beginning sector to the end. By thus reading and storing the sectors linearly, seek operations are minimized. Hence, the backup time is typically reduced in comparison with the file-based backup technique.
Some examples of conventional backup media are magnetic tapes, magnetic disks, optical disks, etc. In performing image backups, conventional image-based backup methods typically use a backup medium that has a larger data capacity than the source disk to be backed up. For example, a backup medium of at least one GB is commonly used to backup a partition of a one Gigabytes (GB) source disk.
As the size of disks increases in size, however, a backup medium may not be able to store an entire image copy of a partition in a disk. This problem is exacerbated for a backup medium having a standardized data storing capacity. For example, optical disk drives such as CD-ROM recordable and rewritable media typically have a maximum capacity of about 650 Megabytes (MB) in accordance with industry standards. When the capacity of a partition to be backed up exceeds the capacity of individual backup medium, the partition is typically backed up over multiple backup media called volumes (e.g., discs). In this case, the image backup is spanned over multiple files or volumes until the entire partition has been backed up. The full group of volumes that make up the full backup data set is often referred to as a backup set.
Unfortunately, however, conventional spanning backup methods have several drawbacks. For example, the conventional spanning method takes substantial amount of time to backup and restore data when used with relatively slow optical disc drives such as CD-ROM rewritable or recordable drives, which are typically characterized by significantly larger seek times than hard disk drives. Since the backup and restore operations are often performed in a non-sequential manner, the larger seek times of the optical disc drives thereby increase the time needed to perform backup and restore operations.
In addition, some conventional backup media such as CD-ROM recordable discs are configured to be written only once. For example, once a data has been recorded on a write-once medium, no data can be written over the recorded data. That is, data may only be added and not edited. When a part of the data that have been written needs to be changed, the entire file needs to be rewritten. This rewriting of the file data directly translates into substantial cost in disc space and time, thereby degrading backup performance.
In view of the foregoing, what is needed is an image backup method and system for backing up data of one or more partitions to support spanning over multiple volumes while optimizing for sequential writing and reading to and from the back up media to save storage space and backup performance.
SUMMARY OF THE INVENTION
The present invention fills these needs by providing a method and system for backing up data over a plurality of volumes. It should be appreciated that the present invention can be implemented in numerous ways, including as a process, an appa
Berhan Michael D.
Evers Daniel L.
Halloran Thomas G.
Polfer Daniel A.
Anderson Matthew D.
Kim Matthew
Martine & Penilla LLP
Roxio, Inc.
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