Electrical computers and digital processing systems: memory – Storage accessing and control – Control technique
Reexamination Certificate
1998-03-25
2002-04-23
Yoo, Do Hyun (Department: 2187)
Electrical computers and digital processing systems: memory
Storage accessing and control
Control technique
C711S162000, C707S793000
Reexamination Certificate
active
06378054
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to a data backup device and method suitable for use with a computer and to a computer-readable recording medium having a data backup program recorded thereon.
(2) Description of the Related Art
In recent years, computers, such as personal computers, as well as computer networks dominantly comprising Internet and personal computer communication, have become prevalent. In association with this tendency, important data sets such as electronic mail or documents stored in a storage device of a computer have also increased.
The contents of the important data sets may be destroyed or become unavailable by the user's faulty operation of the computer or by a breakdown in the storage device. The loss of data results in significant damage in terms of time and money.
In a method of minimizing damage by immediately recovering a data file in the event of problems such as the loss of data, a technique of duplicating information (i.e., a data backup technique) becomes important.
As shown in
FIG. 18
, a computer
50
comprises a predetermined storage device
51
and a backup storage device
52
. Data which are identical to the data stored in the storage device
51
are stored in the storage device
52
, thereby preventing the foregoing damage.
With regard to common data backup methods, there are various data backup methods which vary among the types of data files to be reproduced (or copied) and the ways the data files are input or output. Each of the methods will now be described.
(a) Data backup methods varying with the types of data files to be copied
These data backup methods are classified into three methods according to the type of data file to be copied; that is, a full backup method, a differential backup method, and an incremental backup method.
(a1) Full Backup Method
According to this method, all the data files stored in an area in storage to be copied are copied at one time.
(a2) Differential Backup Method
According to this method, among the data files stored in an area in storage to be copied, the data files copied are those whose data have been updated or which have been newly created since the last backup version was created by full backup.
(a3) Incremental Backup Method
According to this method, among the data files stored in an area in storage to be copied, only the data file copied are those whose data have been updated or which has been newly created since the last backup version was created by full backup or differential backup.
(b) Data backup methods varying with the ways a data file is input or output
The processing time required for the data backup method is determined by a method of inputting or outputting a data file required when the data file is copied. The inputting and outputting of one data file involves open processing, read/write processing, and close processing. With reference to
FIG. 19
, an explanation will be given of copying of a file A stored in the storage device
51
(for holding the original file) to a file A′ stored in the storage device
52
(for holding a copied file).
More specifically, the open processing is a process for making a data file available by extraction of information about the data file; e.g., the location of the data file in the storage device, the date on which the file was created, or the size of the data file.
The read/write processing is a process for reading contents from or into a data file and is designed to write the data read from the file A to the file A′. The close processing is a process for terminating utilization of a data file and is designed to discard information about the data file extracted at the time of open processing.
The following explanation describes the three types of data backup methods that vary with the file input-output processing methods.
(b1) Data Backup Method Utilizing Disk Image
Under this method, data are directly read from the storage device and written on another storage device without regard to a data structure configured in the storage device. For example, as shown in
FIG. 20
, raw data stored in the storage device
51
are stored in the storage device
52
, exactly as they are.
Since this method disregards the data structure configured in the storage device, there is no need to execute open/close processing for the purpose of inputting or outputting data on a file-by-file basis, thus resulting in a reduction in processing time.
(b2) Data Backup Method Utilizing File Image (
1
)
Under this method, data are read on a file-by-file basis, and the thus-read data are written into another storage device on a file-by-file basis according to the data structure configured in the storage device. For example, as shown in
FIG. 21
, data concerning files A, B, and C stored in the storage device
51
are stored, respectively, in the storage device
52
on a file-by-file basis.
In short, this method enables data to be copied or restored on a file-by-file basis according to the data structure configured in the storage device and can be applied to the foregoing differential or incremental backup method.
(b3) Data Backup Method Utilizing File Image (
2
)
Under this method, data are read on a file-by-file basis according to the data structure configured in the storage device, and the thus-read data files are grouped into one data file. The data files are written into another storage device on a file-by-file basis. For example, as shown in
FIG. 22
, all the data sets concerning the files A, B, and C stored in the storage device
51
are collectively stored in the storage device
52
.
This method enables data to be copied or restored on a file-by-file basis according to the data structure configured in the storage device. Further, since this method permits the data files read from the storage device
51
to be grouped into one data file and to be written into the storage device
52
, execution of the open and close processing is required to be performed only once, collectively, in order to write the data files into the storage device
52
.
More specifically, many commercially-available data backup software packages employ the foregoing method (b2). For example, a backup software package bundled with MS-Windows 95, which is commercially available from Microsoft Co., Ltd. and is an operating system (OS) for use in a personal computer, employs the data backup method (b2). In addition, ASCserver and Cheyenne Backup, which are available from Computer Associates Ltd., and Seagate Backup, which is available from Seagate Co., Ltd., also employ the foregoing method (b2).
In a case where user data comprising electronic mail or documents are copied in a personal computer which uses a 32-bit Pentium microprocessor of 90 MHz, through use of the backup software package bundled with MS-Windows 95, the processing rate determined from the processing time required to copy the data by measurement is 185 KB/s.
The foregoing data backup methods suffer the following problems. First, as mentioned previously in section (a) entitled “Data backup methods varying with the types of data files to be copied,” under the differential or incremental backup method, if data are copied several times, there are required recording mediums having backup operations or backup data files recorded thereon in the number corresponding to the number of times the data are copied, resulting in an increase in the number of recording mediums. Further, in this case, when the copied data files are restored, they must be restored in the order in which they were copied.
To solve the foregoing problem, the number of backup data files or recording mediums must be reduced, and the copied data files must be restored in a simple manner. Accordingly, all the data files must be copied after the differential or incremental backup operation has been performed for a given period of time. In order to reduce the overall processing time required by a data backup system, the processing time required for the full backup operation must be reduced.
Next, in the case of data back
Karasudani Akira
Nakano Yasuhiko
Okada Yoshiyuki
Fujitsu Limited
Portka Gary J.
Staas & Halsey
Yoo Do Hyun
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