U.S. patent application number 11/752802 was filed with the patent office on 2007-09-20 for raid overlapping.
Invention is credited to Seiji Kobayashi, Toshiyuki Sanuki.
Application Number | 20070220206 11/752802 |
Document ID | / |
Family ID | 33535044 |
Filed Date | 2007-09-20 |
United States Patent
Application |
20070220206 |
Kind Code |
A1 |
Kobayashi; Seiji ; et
al. |
September 20, 2007 |
RAID Overlapping
Abstract
A first array of disk drives overlaps with a second array of
disk drives in a Redundant Array of Inexpensive Drives (RAID)
system, in which the first and second arrays share at least one
disk drive. A first stripe of data from a first client is stored in
the first array, and a second stripe of data from a second client
is stored in the second array. The shared disk drives are less than
the number of drives needed to reconstruct a full stripe. Thus, in
the event of a drive failure in the first array, the first client
can reconstruct the first data stripe, but is never able to
reconstruct the second stripe. Likewise, in the event of a drive
failure in the second array, the second client can reconstruct the
second data stripe, but is never able to reconstruct the first
stripe.
Inventors: |
Kobayashi; Seiji;
(Kanagawa-Ken, JP) ; Sanuki; Toshiyuki; (Kanagawa,
JP) |
Correspondence
Address: |
DILLON & YUDELL LLP
Suite 2110
8911 North Capital Of Texas Highway
Austin
TX
78759
US
|
Family ID: |
33535044 |
Appl. No.: |
11/752802 |
Filed: |
May 23, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10872059 |
Jun 18, 2004 |
|
|
|
11752802 |
May 23, 2007 |
|
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Current U.S.
Class: |
711/114 ;
714/E11.034 |
Current CPC
Class: |
G06F 11/1084 20130101;
H04N 21/2318 20130101; H04N 21/2182 20130101 |
Class at
Publication: |
711/114 |
International
Class: |
G06F 12/00 20060101
G06F012/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 24, 2003 |
JP |
JP2003-179042 |
Claims
1. A method comprising: overlapping a first array of storage
devices with a second array of storage devices, such that the first
array and the second array of storage devices share at least one
storage device; storing a first stripe of data from a first client
in the first array of storage devices; and storing a second stripe
of data from a second client in the second array of storage
devices, wherein, in response to one of the storage devices in
either the first array or the second array failing, the first
array, including the shared at least one storage device, is able to
reconstruct the first stripe of data but is unable to reconstruct
the second stripe, and wherein the second array, including the
shared at least one storage device, is able to reconstruct the
second stripe but is unable to reconstruct the first stripe.
2. The method of claim 1, wherein the first and second arrays of
storage devices are in a Redundant Array of Inexpensive Drives
(RAID) system.
3. The method of claim 2, wherein the RAID system is a RAID5
system.
4. A computer program product, residing on a computer usable
medium, comprising: computer program code for overlapping a first
array of storage devices with a second array of storage devices,
such that the first array and the second array of storage devices
share at least one storage device; computer program code for
storing a first stripe of data from a first client in the first
array of storage devices; and computer program code for storing a
second stripe of data from a second client in the second array of
storage devices, wherein, in response to one of the storage devices
in either the first array or the second array failing, the first
array, including the shared at least one storage device, is able to
reconstruct the first stripe of data but is unable to reconstruct
the second stripe, and wherein the second array, including the
shared at least one storage device, is able to reconstruct the
second stripe but is unable to reconstruct the first stripe.
5. The computer program product of claim 4, wherein the first and
second arrays of storage devices are in a Redundant Array of
Inexpensive Drives (RAID) system.
6. The computer program product of claim 5, wherein the RAID system
is a RAID5 system.
Description
PRIORITY CLAIM
[0001] This application claims priority of Japanese Patent
Application No. 2003-179042, filed on Jun. 24, 2003, and entitled,
"Server, Computer Apparatus, Data Processing Method and
Program."
[0002] The present application is a continuation of U.S. patent
application Ser. No. 10/872,059 (Attorney Docket No.
JP920030130US1) filed on Jun. 18, 2004, and entitled "Raid
Overlapping," which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0003] 1. Technical Field
[0004] The present invention relates to a technique for sharing a
computer resource provided on a network among plural users, and
more particularly to data protection when a storage device is
shared.
[0005] 2. Description of Related Art
[0006] Nowadays, a variety of services have been made available,
including a hosting service for lending computer resources (server,
storage device, circuit, application and so on) provided on a
network, using the network such as the Internet that is widely
spread and a utility computing service in which computer resources
can be purchased by a necessary amount, as needed. These services
reduce a load on the economy and human resources for maintaining
the computer resources from the viewpoint of the user, and are
meaningful for the company, because the company is relieved of the
load or waste by outsourcing them.
[0007] As one of the hosting/utility computing services, there is a
service for providing a data storage area of the storage device to
the user. In this service, it is important to assure the
reliability (fault or failure counter plan) and safety (measure to
prevent leakage of information to other companies) of information
recorded in the storage device. As a failure counter plan, there is
a technique for recording the record information with redundancy,
including the RAID (Redundant Arrays of Independent Disks).
[0008] On the other hand, the existent schemes for preventing
leakage of data include the encryption of recorded data and the
access control (authentication). Moreover, to be safer, there is a
method for physically separating the recording medium for writing
information for each user. For example, information of each user is
recorded on different magnetic disk assigned to each user, when the
storage device is a magnetic disk device.
[0009] FIG. 10 is a diagram showing a hosting server in which
physically different magnetic disks are assigned to plural
companies.
[0010] As shown in FIG. 10, the hosting server has a disk pool
composed of plural magnetic disk devices. Data from different
companies are stored in different magnetic disks, such that
information Aa of client A is stored in magnetic disks for client
A, information Ba of client B in magnetic disks for client B, and
so on. In FIG. 10, for example, information Aa of client A is
divided into four blocks of data Aa1, Aa2, Aa3 and Aa4, with the
parity data added, and are stored in five magnetic disks.
[0011] In the conventional hosting service, various methods for
assuring the safety of recorded data are taken. However, in the
case where the recording medium is shared among plural users to
permit only the maintenance under access control, all the
information for the users sharing the recording medium may be
accessed, if the access control is broken.
[0012] Also, when the recording media for recording data for each
user are physically separated, it is not possible for plural users
to share individual recording medium. That is, the recording medium
assigned to a certain user is only usable to record the information
of the user, even if a large empty area remains. Therefore, the
recording medium has a lower utilization efficiency.
[0013] Thus, it is an object of the invention to assure the safety
of recorded data while sharing the recording medium among plural
users, and improve the utilization efficiency of the recording
medium.
SUMMARY OF THE INVENTION
[0014] In order to achieve the above object, the present invention
is implemented as a server with the following constitution. That
is, the server provides a storage area of a storage device that is
a computer resource via a network to the client, comprising a
storage device group composed of plural storage devices, and a data
processing unit, in response to a write request from the client,
for dividing the write data included in the write request so that
concatenating the divided data may restore the original
information, and for writing the data so that the plural storage
devices storing the write data of each client may partly overlap
with each other.
[0015] Also, this invention is implemented as a computer apparatus
with the following constitution. That is, the computer apparatus
comprises a storage device group composed of plural storage
devices, and a data processing unit for reading or writing data
from or into the storage devices. And this data processing unit,
when writing data into the storage devices, divides each data file
into plural pieces of divided data so that concatenating the
divided data may restore the original information, and writes the
data so that storage devices storing the divided data of a certain
data file and storage devices storing the divided data of another
data file may partly overlap.
[0016] Moreover, this invention is implemented as a computer
apparatus comprising a disk array composed of plural magnetic disk
devices, and a data processing unit for reading or writing data
from or into the disk array. In this computer apparatus, the disk
array stores plural divided data processed by dividing each data
file so that concatenating the divided data may restore the
original information, in such a way that magnetic disk devices
storing a certain data file and magnetic disk devices storing
another data file may partly overlap.
[0017] Also, in order to achieve the above object, another
embodiment of the present invention is implemented as a data
processing method for enabling a computer to write data received
from a certain client via a network into a storage device group
composed of plural storage devices as configured in the following
way. This data processing method comprises a first step of, in
response to a write request from the client, dividing the write
data included in the write request into plural divided data so that
concatenating the divided data may restore the original
information, and a second step of storing the divided data into the
storage device group so that the plural storage devices storing the
write data of each client may partly overlap with each other.
[0018] Further, in the server, the computer apparatus and the data
processing method according to the invention, when the write data
(data file) is divided, there is a redundancy to enable restoration
of the original data file even if part of the divided data is lost.
In this case, the data is written so that the number of storage
devices overlapping storage devices (magnetic disk devices) storing
another write data (data file) may be insufficient to restore the
original data file.
[0019] Preferably, when the write data (data file) is divided, the
division number or the size of divided data (data length, block
length) is changed for each client making the write request, each
data file or each divided data. Furthermore, the divided data is
encrypted or scrambled for writing. In this way, the user who is
accessible to a certain data file is more securely prevented from
acquiring another data file that is not permitted to access,
whereby the data file stored in the storage device has higher
safety.
[0020] Moreover, this invention is implemented as a program for
controlling a computer to perform various functions, or the
processes corresponding to steps in the data processing method.
This program may be stored and distributed in a magnetic disk, an
optical disk, a semiconductor memory or other storage media, or
distributed via a network.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 is a typical block diagram showing an example of the
hardware configuration of a computer apparatus for implementing a
hosting server for use in an embodiment of the invention;
[0022] FIG. 2 is a diagram showing the functional configuration of
a hosting server implemented by the computer apparatus according to
the embodiment as shown in FIG. 1;
[0023] FIG. 3 is a diagram showing a method for dividing data into
plural blocks and writing divided blocks of data into plural disks
that are distributed, using a RAID5;
[0024] FIG. 4 is a view for explaining whether or not to restore
the original data when data is written using the RAID5;
[0025] FIG. 5 is a diagram showing a method for writing data into a
disk array according to the embodiment;
[0026] FIG. 6 is a flowchart for explaining the operation of a data
write process by the hosting server according to the
embodiment;
[0027] FIG. 7 is a diagram showing the data flow in writing
data;
[0028] FIG. 8 is a flowchart for explaining the operation of a data
read process by the hosting server according to the embodiment;
[0029] FIG. 9 is a diagram showing the data flow in reading data;
and
[0030] FIG. 10 is a diagram showing the hosting server in which
physically different magnetic disks are assigned to plural
companies.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0031] The preferred embodiments of the present invention will be
described below in detail with reference to the accompanying
drawings.
[0032] FIG. 1 is a block diagram showing an example of a hardware
configuration of a computer apparatus for implementing a hosting
server for use in an embodiment of the invention.
[0033] The computer apparatus as shown in FIG. 1 comprises a CPU
(Central Processing Unit) 101 that is operation means, a main
memory 103 connected via an M/B (Mother Board) chip set 102 and a
CPU bus to the CPU 101, a video card 104 connected via the M/B chip
set 102 and an AGP (Accelerated Graphics Port) to the CPU 101, a
magnetic disk device (Hard Disk Drive--HDD) 105 connected via a PCI
(Peripheral Component Interconnect) bus to the M/B chip set 102, a
network interface 106, and a floppy disk drive 108 and a
keyboard/mouse 109 connected via the PCI bus, a bridge circuit 107
and a low speed bus such as an ISA (Industry Standard Architecture)
bus to the M/B chip set 102.
[0034] FIG. 1 only exemplifies the hardware configuration of the
computer apparatus for implementing this embodiment, but various
other configurations may be taken, as far as this embodiment is
applicable. For example, the video card 104 is not provided, but a
video memory may be only mounted to process the image data in the
CPU 101. As an external storage device, a CD-R (Compact Disc
Recordable) or DVD (Digital Versatile Disc) drive may be provided
via an interface such as ATA (AT Attachment) or SCSI (Small
Computer System Interface).
[0035] In this embodiment, the magnetic disk device 105 is employed
as the storage device storing the information of the user.
Accordingly, plural magnetic disk devices 105 are prepared to
compose a disk array.
[0036] FIG. 2 is a diagram showing the functional configuration of
the hosting server implemented by the computer apparatus according
to the embodiment as shown in FIG. 1.
[0037] Referring to FIG. 2, the hosting server of this embodiment
comprises a disk array 40 composed of plural disks (corresponding
to the magnetic disk devices 105 in FIG. 1), an I/O (Input/Output)
controller 10 for transmitting a request or receiving a response to
or from the client (service user), a data/disk management unit 20
for managing various kinds of data or the disk information, and a
data processing unit 30 for reading or writing data from or into
the disk.
[0038] Of the components as shown in FIG. 2, the I/O controller 10
and the data processing unit 30 are software blocks implemented by
the CPU 101 that is controlled by the program as shown in FIG. 1.
Also, the data/disk management unit 20 consists of the CPU 101
controlled by the program and storage means such as the main memory
103, the magnetic disk device 105 and a cache memory provided in
the CPU 101. The program for controlling the CPU 101 to perform the
functions is stored and distributed in a magnetic disk, an optical
disk, a semiconductor memory or other recording media, or may be
distributed via the network.
[0039] The I/O controller 10 accepts a read or write request from
the client via the network interface 106 of FIG. 1, for example,
and issues an instruction to the data/disk management unit 20 and
the data processing unit 30. And the I/O controller 10 receives a
completion notice of the write process or the read data from the
data processing unit 30, and returns a response to the prior
request via the network interface 106 to the client. A specific
operation of the data writing or reading process will be described
later.
[0040] The data/disk management unit 20 comprises a cache processor
21, a disk array logical model manager 22, and a data division
number/coding policy generator 23, as shown in FIG. 2.
[0041] The cache processor 21, in response to an instruction from
the I/O controller 10, collects the information necessary for
operating the data processing unit 30 and passes it to the data
processing unit. Also, the information acquired through a previous
process is cached in the cache memory of the CPU 101 or the main
memory 103. The cache processor 21 makes the processing faster when
data is written or read for the same client.
[0042] The disk array logical model manager 22 creates and manages
a logical model (disk array logical model) for managing at which
position the data of each client is recorded in all the disks
composing the disk array 40. The created disk array logical model
is stored in a predetermined area of the main memory 103 or the
magnetic disk 105.
[0043] The data division number/coding policy generator 23 defines,
for each client, the data division number indicating the number of
dividing data in writing data and the coding policy indicating the
coding method (including a coding function or parameters) for
encoding the data. Herein, the data division number means the
number of dividing data to be distributed and written into plural
disks of the disk array 40. For example, write data is divided into
four blocks, with the parity data added, and are distributed and
written into five disks. The generated data division number and
coding policy are stored in a predetermined area of the main memory
103 or the magnetic disk device 105.
[0044] The data processing unit 30 comprises a write processing
unit 31 for writing data and a read processing unit 32 for reading
data, as shown in FIG. 2.
[0045] The write processing unit 31 acquires the disk position,
data division number and coding policy from the data/disk
management unit 20, and divides the write data received from the
I/O controller 10, based on these pieces of information, whereby
the divided data is encoded and written into a desired disk of the
disk array 40.
[0046] The read processing unit 32 acquires the disk position, data
division number and coding policy from the data/disk management
unit 20, and reads the desired data from the disk array 40, based
on these pieces of information, whereby the read data is
concatenated, decoded and passed to the I/O controller 10.
[0047] The disk array 40 is composed of plural disks, as previously
described. And the client data is distributed and recorded into
plural disks. In this case, the distributed and recorded data is
totally or partly collected to restore the original data.
[0048] FIGS. 3 and 4 are diagrams showing a method for dividing
data into plural blocks and writing divided blocks of data into
plural disks that are distributed, using the RAID 5.
[0049] In the RAID 5, data is divided into block units, and
recorded in plural disks that are distributed, with the parity data
recorded in another disk, as shown in FIG. 3. In this case, if one
disk fails, the original data is restored from the divided data of
block units on the remaining disk, as shown in FIG. 4A. On the
other hand, when two or more disks are not accessible, the original
data is not restored correctly, as shown in FIG. 4B.
[0050] Herein, the method for writing data into the disk array 40
according to the embodiment will be described below in detail.
[0051] To generalize the division and coding in writing data into
the disk array 40, it is supposed that the information of k bits is
encoded with code length n and error correction capability t, and
data is written into n disks that are distributed. That is, when
the divided data is unreadable from t disks among n disks, the data
written in the disk array 40 has a redundancy that the original
data can be restored from the remaining divided data of n-t bits.
In this case, the disk position of write destination is controlled
so that the number of disks shared with another client may be equal
to or less than n-(t+1) where the data of certain client is written
into n disks in this embodiment.
[0052] In this way, if another client takes out the data of another
client from the disk shared to acquire the data of n-(t+1) bits,
the original data is not resynthesized correctly because the error
correction capability is t bits. Of course, it does not matter that
the information amount recordable in one disk is one bit or more.
The coding systems with error correction capability may include,
for example, a cyclic code, a BCH code and an RS code.
[0053] In the case where data is recorded using the RAID 5, as
shown in FIGS. 3 and 4, if there are two or more inaccessible
disks, the original data is not restored correctly, as described
above. Thus, two or more disks without overlapping write data are
provided in writing data of each client.
[0054] FIG. 5 is a diagram showing a method for writing data into
the disk array 40 according to the embodiment.
[0055] In FIG. 5, among m disks (41a to 41m) composing the disk
array 40, the disks 41a to 41e are assigned to recording the
information of client A (Aa and Ab). Also, the disks 41c to 41g
shifted by two to the right are assigned to recording the
information (Ba) of client B. Likewise, the disks 41e to 41i are
assigned to recording the information (Ca) of client C, and the
disks 41m-2 to 41m and the disks 41a, 41b are assigned to recording
the information (Na) of client N.
[0056] For example, in writing the write data sent from the client
A, the data is divided into four blocks (Aa1 to Aa4, Ab1 to Ab4) by
the write processing unit 31 in the data processing unit 30, with
the parity data (Aap, Abp) added, and written into five disks 41a
to 41e. It is possible to arbitrarily decide in which disk the
divided data and parity data are stored among assigned disks. In an
example of FIG. 5, the parity data Aap added to the information Aa
of client A is written in the disk 41e, while the parity data Abp
added to the information Ab is written in the disk 41d.
[0057] If the data of each client is written in the above way, the
original data of another client is prevented from being restored
correctly, even though a certain client can access the divided data
written by another client by breaching the access control.
[0058] By the way, in the case where the information is written
into plural disks that are distributed, for example, if information
of one bit is described in each of n disks using the code (n, k,
t), the original data is restored by retrieving all the data with a
computation amount of O(2.sup.t+1), as far as the (n, k, t) coding
system is known. As a measure for avoiding such an incorrect read,
the method for distributing and writing data is changed for each
client, or the disk utilization efficiency is lowered to have a
smaller number of disks that are shared among plural clients. To
change the data writing method involve changing the number of
dividing the data for each client, encrypting and scrambling the
divided data, changing the block length (data length) of divided
data for each client, and other various methods.
[0059] The operation of data processing in the hosting server
according to the embodiment will be described below.
[0060] FIG. 6 is a flowchart for explaining the operation of the
data write process by the hosting server according to the
embodiment, and FIG. 7 is a diagram showing the data flow in
writing data.
[0061] When a request for writing data from a certain client is
delivered to the hosting server, the client information for
specifying the client and a file name of the write data are
extracted from the write request by the I/O controller 10, and sent
to the data/disk manager 20. Also, the write data contained in the
write request is sent to the data processing unit 30 (step
601).
[0062] If the data/disk management unit 20 accepts the client
information and the file name, the cache processor 21 acquires the
disk position, data division number and coding policy for the
client that are specified based on those pieces of information
(step 602). More specifically, first of all, it is checked whether
or not those pieces of information are cached in the cache
processor 21 itself. If not cached, an inquiry about those pieces
of information is made to the disk array logical model manager 22
and the data division number/coding policy generator 23 (see FIG.
7).
[0063] When the disk array logical model has information of disk
position for the client, the disk array logical manager 22 passes
its information to the cache processor 21. On the other hand, when
the disk array logical model does not have the desired information,
the disk array logical model manager 22 defines a new disk
position, and adds it to the disk array logical model, as well as
passing it to the cache processor 21.
[0064] Also, when the data division number/coding policy generator
23 holds the data division number and the coding policy for writing
data of the client, the data division number/coding policy
generator 23 passes its information to the cache processor 21. On
the other hand, when the desired data division number and coding
policy are not held, the data division number/coding policy
generator 23 defines and holds a new data division number and
coding policy, and passes them to the cache processor 21.
[0065] The cache processor 21 acquires the cache data, or desired
information of disk position, data division number and coding
policy corresponding to the write request from the disk array
logical model manager 22 and the data division number/coding policy
generator 23, and then passes these pieces of information to the
data processing unit 30 (see FIG. 7). When these pieces of
information are acquired from the disk array logical model manager
22 and the data division number/coding policy generator 23, the
cache processor 21 newly caches the acquired information. When the
cache capacity of the cache processor 21 is fail, no hit cache data
is deleted in the order from the oldest data, whereby the empty
capacity is kept and the acquired information is cached.
[0066] If the information of disk position, data division number
and coding policy are obtained in the above way, the write
processing unit 31 for the data processing unit 30 divides and
encodes the write data, using these pieces of information (step
603), and write data into the disk array 40 (step 604). And after
the writing of data is ended, a write completion notice is issued
from the write processing unit 31, and returned via the I/O
controller 10 to the client making the write request (step
605).
[0067] FIG. 8 is a flowchart for explaining the operation of a data
read process by the hosting server according to the embodiment, and
FIG. 9 is a diagram showing the data flow in reading data.
[0068] When a request for reading data from a certain client is
delivered to the hosting server, the client information for
specifying the client and a file name of the read data are
extracted from the read request by the I/O controller 10, and sent
to the data/disk management unit 20 (step 801).
[0069] If the data/disk management unit 20 accepts the client
information and the file name, the cache processor 21 acquires the
disk position of the client, the data division number and the
coding policy that are specified based on these pieces of
information (step 802). The specific operation of acquiring these
pieces of information is the same as described in the data write
process (see FIG. 9).
[0070] If the information of disk position, data division number
and coding policy are obtained in the above way, the read
processing unit 32 for the data processing unit 30 reads data from
the disk array 40, using these pieces of information (step 803),
and the read data is concatenated and decoded (step 804). And the
decoded read data is sent from the read processing unit 32 to the
I/O controller 10, and returned to the client having made the read
request (step 805).
[0071] The hosting server of this embodiment provides the computer
resources to the client via the network, but may be applied to
various conventional services in its service form. More
specifically, it may be applied to the on-demand disk providing
service, for example.
[0072] For most companies, if the IT resources such as hardware
resources of the computer are possessed and managed within its own
company, there is a great load on the economy and human resources.
Therefore, for the management of such resources, it is common to
ask other companies for outsourcing or hosting. Thus, for such
companies, the hosting server of this embodiment is employed for
the on-demand disk providing service to provide the storage area of
disk as the storage location of data, as needed.
[0073] In this case, in providing the disk to plural companies, a
huge disk pool (disk array 40) is prepared for each company to
designate a disk group accessible in response to a request from
each company. One data file of the company is distributed and
written into the designated disk group, and the original data file
is restored by reintegrating the disk group. A part of the disk
group assigned to one company is shared with other companies, but
the number of shared disks is limited. Thereby, even if a certain
company gaining access to the disk assigned to its company can
access a part of the data file distributed for another company, the
information of the data file is not completely resynthesized. On
the other hand, for the hosting server, individual disks in the
disk pool are shared among plural companies, whereby the storage
area of the disk is provided to more companies to have the higher
utilization ratio than when individual disks are assigned to each
company.
[0074] Also, another application example of the hosting server
according to this embodiment is a data temporary saving service.
When the data reduction or system change/management or integration
or disintegration is made within the company, it is required to
temporarily save or back up the data. In this case, for the reason
of assuring higher safety against data loss or lack of resources
(storage capacity of disk) in the company computer system, it is
considered that the company data is temporarily saved in the huge
disk pool in the outside data center. When plural companies employ
this service, the hosting server of this embodiment is applied to
prevent leakage of the information of each company within the data
center to other companies.
[0075] In the hosting server of this embodiment, the same disk is
physically shared among plural companies. However, even though a
certain company can read the divided data of another company
written on the accessible disk, the original data is not restored
from the divided data, and the information is not leaked.
Therefore, it is allowed to share the disk among plural companies
while keeping the safety of information temporarily saved, whereby
the utilization efficiency of resources in the data center is
enhanced.
[0076] In this embodiment, the hosting server has the disk array
composed of plural magnetic disk devices as the storage device.
However, this embodiment may be also applicable to the storage
device using various storage media other than the magnetic disk
device in the server or computer apparatus having the storage
device group composed of plural storage units. Also, in this
embodiment, the data to be stored may be not only the write data in
response to a write request from the client but also plural data
files required to regulate the user accessible to each data file.
That is, each data file is stored in plural storage devices
distributed so that the storage devices storing individual data
files may partly overlap with each other, whereby the access
control is more reliable, and the safety of stored data file is
assured.
[0077] As described above, with this invention, while the recording
medium is shared among plural users, the safety of recorded data is
assured, and the utilization efficiency of the recording medium is
enhanced.
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