JP2001290713A - Storage device system and backup acquisition method thereof - Google Patents

Abstract

(57) [Summary] To obtain a copy of user data at a certain point in time while continuously receiving a data write request from a host computer. A write process reads data from a user volume when a copy of a target block for a write request is not completed, and writes the data to a work volume.
Save to 12 The copy process 105 determines whether the data to be copied is in the user volume 110 or the work volume 112, reads the data, and transfers the data to the magnetic tape device 117.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a storage system in a computer system, and more particularly to a storage system capable of obtaining data backup without a host computer.

[0002]

2. Description of the Related Art Generally, in a computer system, data stored in a storage device is backed up in order to prevent important data from being completely lost when a failure occurs in the storage device. I have. In order to guarantee the consistency of the data to be backed up, normally, during the backup, the data write processing to the storage device must be stopped.

[0003] A storage device that solves such a problem and that can perform backup processing without the intervention of a host computer is disclosed in, for example, Japanese Patent Laid-Open No. 7-210.
No. 439.

[0004] The storage device disclosed in Japanese Patent Application Laid-Open No. 7-210439 includes (1) means for managing an area to be backed up by dividing it into a backed up area and an unbacked up area, and (2) an unbacked up area. Means for reading out the data recorded in the area to be written and saving the data in a buffer when a write request for the area is received, and thereafter receiving the write data and recording it on the storage medium; (3) backup means Means for transferring the data to be transferred to another storage device, identifying whether the data to be transferred is in the storage medium or in the buffer, and transferring the data at the start of the backup; (4) saving the data to the buffer Means for actively transferring the save data to another storage device at the backup destination when the data exceeds an appropriate amount; If storage was sequential access format, it comprises means for transferring the data, together with position information indicating where the was recorded in the data storage medium to another storage device.

In this storage device, in order to prevent the buffer from being filled by the means (4), if the storage device for storing backup data is of a sequential access type, there is a problem that data is not recorded in a correct order. In this regard, the means (5) enables restoration based on position information without storing data in a sequential access format storage device in a correct order.

[0006]

However, according to the technique disclosed in Japanese Patent Application Laid-Open No. Hei 7-210439, when the storage device for storing backup data is of a sequential access format, data position information is created. Processing overhead is required. Further, in addition to the data, it is necessary to transfer and store the position information, and accordingly, there is a problem that the storage device for storing the backup data requires a storage capacity.

Further, according to the technique disclosed in Japanese Patent Application Laid-Open No. 7-210439, when a write request occurs during backup, data before being updated by the write request is saved in a buffer, so that the data is stored in the backup destination storage device. When transferring data, it is necessary to manage whether the data to be transferred is in a storage medium or in a buffer. There is also a problem that the management items such as which area of the buffer is open and which area of the data have been saved in order to save the data before update are increased.

An object of the present invention is to provide a storage device which stores backup data in a correct order and eliminates the need to record data position information even when the storage device for storing backup data is a storage device of a sequential access format. To provide.

Another object of the present invention is to provide a storage device which simplifies management of saved data.

[0010]

In order to achieve the above object, according to the present invention, in response to an instruction from a host, data stored in an area indicated by an instruction in a volume is stored in another storage device. In a storage device system having a function of transferring data to another storage device and transferring a backup to another storage device, the specified area is copied to another storage device, and the data is not copied to another storage device. It is divided into an area where the data has been saved in the data saving volume and an area where the data has not been copied to another storage device and the data has not been saved to the data saving volume. If a write request is received for an area that is not copied to another storage device and data has not been saved to the save volume, After the data held in the target area of the write request is stored in the data evacuation volume, the write request execution means for receiving the write data, and whether the data to be transferred to another storage device is in the area in the volume. A copy source management unit that manages whether the data is in a data saving volume; and a copy unit that transfers data at a location obtained by the copy source management unit to a storage device designated by an instruction.

According to another aspect of the present invention, there is provided a user volume storing user data used by a computer, and the data of the user volume is copied when the data of the user volume is copied to another storage device to obtain a backup. There is provided a backup method in a storage device system including a work volume used for evacuation and a control device for controlling access to a user volume and a work volume. In this backup method, in response to a request to copy data from a user volume to another storage device, the user data stored in the area specified by the copy request is copied from the user volume to another storage device. . During a copy process to another storage device, when there is a data write request to a part of the designated area, the user data held in the part of the area is transferred to the work volume. Thereafter, data is written to some areas. In the copy processing, whether the user data to be copied to another storage device is held in the area in the user volume,
It is determined whether the data is held in an area in the work volume, and the user data to be copied is read and transferred to another storage device according to the result of this determination.

[0012]

FIG. 1 is a block diagram showing a configuration example of a computer system including a storage device to which the present invention is applied.

The computer system according to the present embodiment issues a read request, a write request, a copy request, and the like to the disk subsystem 118 storing the user data and the disk subsystem 118 for the user data stored therein. It has a host computer 116 for issuing data and a magnetic tape device 117 for storing backup data of data stored in the disk subsystem 118.

The disk subsystem 118 controls the host interface 102 serving as an interface with the host computer 116, the magnetic tape device interface 104 serving as an interface with the magnetic tape device 117, and various processes performed in the disk subsystem 118. Processor 108, control processor 10
Control memory 10 for storing control information used by
9 and a volume access unit 114 for accessing a volume which is a storage device for storing data.

The control processor 108 has volume attribute change processing 101, write processing 103, and copy processing 105 as processing functions related to backup processing in the present embodiment. These processing functions are specifically realized by a program executed by the control processor 108. The control processor 108 also has various functions for controlling the disk subsystem, but these are not directly related to the present invention.
Here, illustration and description are omitted. Among these processing functions, the volume attribute change processing 101
Are not used in the first embodiment. The volume attribute change processing 101 will be described in a second embodiment described later.

The control memory 109 stores, as control information used in the backup processing in this embodiment,
Volume management information 106 and copy status management information 10
7 is held.

The disk subsystem 118 has, as volumes serving as data storage devices, user volumes 110 and 111 for storing user data and work volumes 112 and 113 for storing backup data during backup processing. . Each volume is provided with a volume number as an identifier for identifying each volume.

In this embodiment and a second embodiment to be described later, a volume refers to a logical storage device formed using a physical disk device and recognized as one storage device by a host computer. . One physical disk device may be used as one volume as it is, or a plurality of volumes may be formed on one disk device. When the disk subsystem 118 is configured as a so-called RAID, a plurality of volumes are formed on a plurality of physical disk devices constituting the RAID.

The storage area of each volume is composed of a plurality of blocks. Each block is assigned a block number as information for identifying each block. The volume has block numbers 0, 1, 2,...
A block having a value of N (N is an integer value of 0 or more and may be different for each volume) is provided.

FIG. 2 is a conceptual diagram showing the data structure of the copy status management information 107.

The copy status management information 107 includes information related to a copy operation. Copy status management information 10
7 is referenced / updated in a write process 103 and a copy process 105 executed in response to a write request issued by the host computer 116 and a copy request.

As shown in the figure, the copy status management information 10
7 is in use flag 300, copy source volume number 3
03, including block information 304. The in-use flag 300 is a flag indicating whether or not the copy status management information 107 is in use, and has a value indicating either “unused” or “in use”. The copy source volume number 303 stores the volume number of the volume storing the data to be copied by the backup process. The block information 304 is information indicating the state of the block of the volume indicated by the copy source volume number 303.

The block information 304 includes a block number 301 and a copy status 302 as information indicating the block status.
Having. The copy status 302 has a value indicating one of “copy unnecessary”, “copy required & not saved”, “copy required & saved”, and “copied”.

"No need to copy" indicates that the block stores data that does not need to be copied. “Copy required & not saved” indicates that the block stores data that needs to be copied at present. “Copy required & saved” indicates that the block that stores the data that needs to be copied when the copy request is received, but that data is saved in the work volume.

FIG. 3 is a conceptual diagram showing the data structure of the volume management information 106.

The volume management information 106 is management information indicating the status of the volume, and has a copy operation presence / absence flag 401 for each volume number 400. The copy operation presence / absence flag 401 takes a value indicating either “during copying” or “normal”. “During copying” indicates that the volume is a target of copy processing. "Normally,
Indicates that the volume is not subject to copy processing.

FIG. 4 is a flowchart showing the flow of the write processing 103 executed in response to a write request from the host computer in the present embodiment.

When writing or updating user data, the host computer 116 issues a write request to the disk subsystem 118. The write request includes the volume number of the volume to which the write data is to be written, the block number of the block to which the write data is to be written, and the write data.

When a write request is received, the control processor 1
08 starts the process by the write process 103.

The control processor 118 first refers to the volume management information 106 to determine whether or not copy processing, which will be described later, is being performed on the data of the volume that is the target of the write request. Specifically, the state of the copy operation presence / absence flag 401 is checked, and the copy operation presence / absence flag 4 is checked.
If 01 indicates "copying", the process proceeds to step 501, and if "normal", the process proceeds to step 504 (step 500).

At step 501, the control processor 118 checks the status of the write request with reference to the copy status management information 107, and determines whether data must be saved. Specifically, the copy status management information 107 storing the same value as the volume number of the volume to be requested for the write request in the copy source volume number 303 is selected. Next, the control processor 118 returns to the copy state 30
2 is checked to see if the block that is the target of the write request is "copy required & not saved". If the copy status 302 indicates "copy required & not saved", the process proceeds to step 502 to save the data. If the copy status 302 is a value indicating a value other than “copy required & not saved”, the process proceeds to step 504 because data saving is unnecessary.

In step 502, first, of the blocks requested to be written, data of a block that is indicated as “copy required & not yet saved” by the copy status 302 is transferred from the user volume 110 to the volume access unit 114. Read. Next, the control processor 11
8 records the read data in the work volume 112. At this time, the control processor 118 writes data to a block of the work volume 112 having the same block number as the block in which the data read in the user volume 110 was stored.

At step 503, the control processor 118
Updates the copy status 302 of the block whose data was saved in step 502 to a value indicating “copy required & saved”.

In step 504, the write data received from the host computer 116 in the write request is recorded in the designated block of the user volume 110, and the process ends.

FIG. 5 is a flowchart showing the flow of the copy processing 105 executed in response to a copy request from the host computer in the present embodiment.

The copy request issued by the host computer 116 has the volume number of the volume storing the data to be copied and the block number of the block storing the data to be copied.

Upon receiving a copy request from the host computer 116, the control processor 118 executes the copy process 10
5 is started.

In the copy processing 105, the control processor 118 selects an entry in which the volume number is set to 400 and the same volume number as the volume number received as a parameter of the copy request from the volume management information 106. Then, a value indicating "copying" is set in the copy operation presence / absence flag 401 of the entry (step 600).

The control processor 118 selects, from the copy status management information 107, copy status management information in which the value indicating “unused” is set in the in-use flag 300,
A value indicating “in use” is set in the in use flag of the selected copy status management information 107. Next, a volume number, which is a parameter of the copy request, is set in the copy source volume number 303. Next, the control processor 118
A value indicating “copy required & not saved” is set in the copy status 302 corresponding to the same block number 301 as the block number designated by the parameter of the copy request, and “copy” is set in the copy status 302 corresponding to the other block numbers 301. A value indicating "unnecessary" is set (step 601).

Thereafter, a variable i for designating a block
Is set to 0, and a variable i is initialized (step 60).
2).

The control processor 118 determines in step 601
In the copy status management information 107 selected in the step 3, the copy status 30 corresponding to the same block number 301 as the value of the variable i.
The process to be executed next is determined by the value of 2. That is,
If the copy status 302 indicates “copy required & not saved”, the process proceeds to step 604. If the copy status 302 indicates “copy required & saved”, the process proceeds to step 605. If the copy status 302 indicates "copy unnecessary" or "copied", the process proceeds to step 607 (step 603).

In step 604, the control processor 118 uses the volume access unit 114 to read data from the block of the user volume 110 having the same block number as the variable i. Control processor 118
Represents the data read from the user volume 110,
The data is transferred to the magnetic tape device 117 via the magnetic tape device interface 104 and recorded on the magnetic tape.

In step 605, data is read from the block of the work volume 112 having the block number matching the variable i by using the volume access unit 114. The control processor 118 transfers this data to the magnetic tape device 117 via the magnetic tape device interface 104, and records the data on the magnetic tape.

After the transfer of the data from the user volume 110 or the work volume 112 to the magnetic tape device 117, the control processor 118 checks the copy status management information 107 to indicate that the data of the block has been copied. A value indicating “copied” is set in the copy status 302 corresponding to the same block number 301 as the variable i (step 606).

At step 607, the user volume 1
It is determined whether the process has been performed for all 10 blocks. If the processing has been completed for all blocks, the process proceeds to step 609. If there are any remaining blocks, the control processor 118 increments the value of the variable i by 1 in step 608, and then proceeds to step 60.
Returning to the processing of step 3, the same processing is performed for the remaining blocks.

In step 609, the in-use flag 30 of the copy status management information 107 selected in step 601 is used.
A value indicating “unused” is set to 0. Finally, the control processor 118 sets a value indicating “normal” in the copy operation presence / absence flag 401 of the volume management information 106,
The copy processing 105 ends.

In the embodiment described here, copy processing is performed in response to a copy request issued from the host computer 116. In addition, disk subsystem 1
The operation terminal 18 may include an operation terminal 100 serving as an interface with the operation terminal 115, and the operation terminal 115 may issue a copy request. In this case, the control processor 10
8 starts a copy process 105 upon receiving a copy request from the operation terminal 115 via the operation terminal interface 100.

As described above, by using a volume as an area for saving data, costs can be reduced as compared with a case where a semiconductor memory such as a buffer is used as a storage medium for saving data. Further, since the data is backed up in the order specified by the copy request, the backup data can be stored in a sequential access type storage medium such as a magnetic tape without using the position information. Thus, it is possible to reduce the overhead of the backup process, the amount of transfer data, and the amount of stored data.

Next, another embodiment of the present invention will be described.

The computer system according to the second embodiment described below has basically the same configuration as that of the first embodiment. In the present embodiment, processing using volume attribute change processing 101 not used in the first embodiment will be described. By using the volume attribute change processing 101, the contents of the control information and the processing to be performed are slightly different from those in the first embodiment.

FIG. 6 is a conceptual diagram showing the data structure of the copy status management information used in the present embodiment. As shown in the figure, in the copy status management information of the present embodiment, a work volume number 700 is added to a busy flag 300, a copy source volume number 303, and block information 304.

The work volume number 700 is a volume number of a volume used as a work volume for saving data during execution of a copy request from the host computer 116 or the operation terminal 115. In the present embodiment, a volume having a volume number held in the work volume number 700 is used as a work volume.

FIG. 7 is a conceptual diagram showing the data structure of the volume management information 106 in the present embodiment. As shown in the figure, the volume management information 106 of the present embodiment includes:
For the volume management information used in the first embodiment,
An attribute flag 800 has been added.

The attribute flag 800 includes a volume number 4
As a flag indicating the attribute of the volume specified by 00, a value indicating either “user” or “work” is set. When the value set in the attribute flag 800 indicates “user”, the volume is used as a user volume for storing user data. on the other hand,
When the attribute flag 800 has a value indicating “work”, the volume is used as a work volume for storing save data.

By issuing a volume attribute change command to the disk subsystem 118, the host computer 116 or the operation terminal 115 can change the volume attribute (attribute such as user volume or work volume). The volume attribute change command includes “volume number” and “attribute” as parameters. The parameter “volume number” is a volume number indicating the volume whose attribute is to be changed. Also, the parameter "Attribute"
Indicates a new attribute of the volume specified by the volume number.

FIG. 8 is a flowchart of the volume attribute change processing 101 executed by the control processor 108 in response to the volume attribute change command.

In the volume attribute change processing 101,
The control processor 108 first sets the volume management information 1
With reference to 06, the copy operation presence / absence flag 401 of the volume corresponding to the parameter "volume number" of the received volume attribute change command is checked (step 1000).

When the copy operation presence / absence flag 401 is "copying", the control processor 108 notifies the requesting host computer 116 or the operation terminal 115 that the attribute cannot be changed, and terminates the processing. (Step 1002).

If the copy operation presence / absence flag 401 is "normal" in step 1000, the control processor 108 changes the attribute flag 800 to the attribute designated by the parameter and ends the processing (step 100).
1).

FIG. 9 is a flowchart of the write process in this embodiment. As shown in the drawing, in the write processing in the present embodiment, the processing in step 502 in the write processing in the first embodiment is performed in step 1100.
And the processing of step 1101 are replaced.

When the data must be saved (the control processor is executing a copy request for the volume requested to be written, and the copy status 302 of the target block of the write request is “copy required & Not evacuated "
In step 1100, the in-use flag 30
0 is “in use” and the volume number of the volume for which the write request was made is the copy source volume number 30
The copy status management information 107 set to No. 3 is acquired. Further, the control processor identifies a volume to be used as a work volume for saving data based on the volume number set in the work volume number 700 of the corresponding copy status management information 107.

At step 1101, data is read from the copy source volume and written to the work volume identified at step 1100, as in step 502 of the first embodiment.

The processes having the same step numbers as in FIG. 4 except for steps 1100 and 1101 are the same as the corresponding steps described in the first embodiment.
Here, the description is omitted.

FIG. 10 is a flowchart of the copy processing according to the present embodiment.

The copy processing of this embodiment is the first in the following points.
Is different from the copy processing in the embodiment. First
Step 1 in place of Step 601 in the embodiment
Steps 200 and 1201 are performed. Step 1202 instead of step 605 in the first embodiment
Is performed. Then, at the end of the process, step 1
Step 203 has been added.

At step 1200, the control processor 108
Refers to the volume management information 106 and selects a volume whose copy operation presence / absence flag 401 is “normal” and whose attribute flag 800 is “work”, that is, an unused work volume. Then, a value indicating “copying” is set in the copy operation presence / absence flag 401 corresponding to the selected volume.

Next, in step 1201, the control processor 108 executes step 6 in the first embodiment.
As in the case of 01, the copy status management information 107 to be used is selected, and each information is set. At this time, in the present embodiment, the volume number of the volume selected in step 1200 is set as the work volume number 700 of the copy status management information 107.

At step 1202, the control processor 108
Reads the data stored in the block having the same block number as the variable i from the volume selected in step 1200. Then, the control processor 108
Transfers the data read via the magnetic tape device interface 104 to the magnetic tape device 117 and records the data on a magnetic tape.

In step 1203, "normal" is set in the copy operation presence / absence flag 401 corresponding to the volume selected in step 1200 in the volume management information 106, and the status of use is released.

For processes other than the processes described here, the same processes as the copy process in the first embodiment are performed. Therefore, the description is omitted here.

According to this embodiment, a command for changing the attribute of a volume is supported, and a user volume for storing user data and a work volume for storing saved data can be switched and used. For this reason,
The number of work volumes can be changed according to the required copy request multiplicity, and volume resources can be used effectively.

When a copy request is received, the disk subsystem selects and uses a work volume to be used for executing the copy request from a group of unused work volumes. When the copy processing ends, the used work volume is returned to an unused state. In this way, by reusing one work volume, the work volume can be effectively used.

Further, the program for issuing a copy request from the host computer or the operation terminal does not need to manage the work volume, so that the program is simplified.

In the first and second embodiments, the save data is stored in the block having the same block number as the user volume in the work volume. However, the save data may be stored in order from the head of the work volume. In this case, the copy status management information 107 may have information indicating which block has been saved, in addition to the information indicating whether the copy has been saved. In the copy process, the location of the save data is checked from this information, the data is read from the corresponding block, and the data is transferred to the magnetic tape device. By doing so, it is sufficient to secure an area for storing the save data for the block indicated by the copy request from the host computer or the operation terminal, and execute the copy request multiple times with a smaller work volume. can do.

When the disk subsystem receives a request to access a volume from the host computer, it checks whether or not the volume is a user volume by referring to volume management information. Execute the access request and if the volume is a work volume,
The host computer may be notified that the volume cannot receive the access request.
By providing such a check mechanism, the disk subsystem can prohibit access to an illegal volume.

According to the embodiment described above, for a block indicated by a copy request, while receiving a write request from the host, the data at the time of receiving the copy request is
The following effects can be obtained in a disk subsystem that backs up to a magnetic tape device or the like without intervening a host.

First, by using a volume as an area for saving data, the cost can be reduced as compared with a semiconductor memory such as a buffer.

Second, since the backup data can be stored in a sequential access type storage medium such as a magnetic tape in the order indicated by the copy request, the position indicating the position where the backed-up data was stored is indicated. There is no need to add information, and it is possible to reduce the overhead of creating position information, reduce the amount of transfer data, and reduce the amount of stored data.

[0079]

According to the present invention, it is possible to obtain a copy of user data at a certain point in time while continuously receiving a data write request from a host computer.

[Brief description of the drawings]

FIG. 1 is a simplified block diagram illustrating a configuration example of a computer system including a storage device to which the present invention has been applied.

FIG. 2 is a conceptual diagram illustrating a data structure of copy status management information according to the first embodiment.

FIG. 3 is a conceptual diagram illustrating a data structure of volume management information according to the first embodiment.

FIG. 4 is a flowchart illustrating a flow of a write process according to the first embodiment.

FIG. 5 is a flowchart illustrating a flow of a copy process according to the first embodiment.

FIG. 6 is a conceptual diagram illustrating a data structure of copy status management information according to a second embodiment.

FIG. 7 is a conceptual diagram illustrating a data structure of volume management information according to a second embodiment.

FIG. 8 is a flowchart illustrating a flow of a volume attribute change process.

FIG. 9 is a flowchart illustrating a flow of a write process according to the second embodiment.

FIG. 10 is a flowchart illustrating a flow of a copy process according to the second embodiment.

[Explanation of symbols]

101: Volume attribute change processing, 103: Write processing, 105: Copy processing, 106: Volume management information, 107: Copy status management information, 108: Control processor, 109 ... Control memory, 110, 111: user volume, 112, 113: work volume,
116: Host computer, 117: Magnetic tape device, 118: Disk subsystem

Continued on the front page (72) Inventor Kenzo Tabata 2880 Kozu, Odawara-shi, Kanagawa F-term in Hitachi, Ltd. Storage Systems Division 5B018 GA04 HA03 KA03 MA11 QA15 5B065 BA01 BA07 CA40 EA02 EA12 EA23 EA33 5B082 DE06 GA15 5B08 AA08 BB01 BB03 CC04 CD11 EE08

Claims (9)

[Claims] 1. A storage device sub-system having a function of transferring data stored in an area indicated by said instruction in a volume to another storage device and acquiring a backup in response to an instruction from a host. In the system, the designated area is divided into an area in which data has been copied to the other storage device, and a copy to the other storage device has not been completed, and data has been saved to a data saving volume. Area management means for separately managing the area and the area in which data has not been copied to the other storage device and data has not been saved to the data saving volume; and If a write request is received for an area that has not been copied to another storage device and data has not been saved to the save volume, the write request After storing the data held in the area in the data evacuation volume, write request execution means for receiving write data, and whether the data to be transferred to the other storage device is in the area in the volume A copy source management unit that manages whether the data is in the data evacuation volume, and a copy unit that transfers data at a location obtained by the copy source management unit to a storage device specified by the instruction. Characteristic storage system. 2. The storage device system according to claim 1, wherein said copy means transfers data to said storage device in an order specified by said instruction. 3. The storage system according to claim 1, further comprising volume switching means for receiving a command for switching between a user volume for storing user data and a work volume for storing save data. 4. A work volume management means having a plurality of data evacuation volumes and managing the use state of the plurality of data evacuation volumes, and is managed by the work volume management means in response to a copy request. A data evacuation volume in an unused state to be selected, and a data evacuation volume allocating means to be allocated for data evacuation, and in response to completion of execution of a copy request,
2. The storage system according to claim 1, further comprising: a data evacuation volume release unit that returns the data evacuation volume used for data evacuation to an unused state. 5. The data save volume according to claim 1, wherein said write request execution means, when saving data to said data save volume, has an area in said data save volume having the same address as an area in said volume in which data to be saved is stored. 2. The storage device system according to claim 1, wherein said data is saved. 6. A user volume storing user data used by a computer, a work volume used for saving data when copying the data of the user volume to another storage device and obtaining a backup, A backup acquisition method in a storage device system comprising: a control device that controls access to the user volume and the work volume; wherein the user device responds to a request to copy data from the user volume to the other storage device. Initiating a copy process of the user data held in the area designated by the copy request from the volume to the other storage device, and during the copy process to the other storage device, When there is a request to write data to some area of Transferring the user data held in the area to the work volume, writing the data to the partial area, and in the copying process, the user data to be copied to the other storage device is the user data. It is determined whether the data is held in the area in the volume or in the area in the work volume, and the user data to be copied is read and transferred to the other storage device according to the result of the determination. A method for obtaining a backup, characterized in that: 7. The storage system includes a plurality of volumes usable as the work volumes, and the step of starting the copy processing includes selecting an unused volume from the plurality of volumes to execute the work. 7. The backup acquisition method according to claim 6, further comprising a process of allocating to a volume. 8. The backup acquisition according to claim 6, wherein the transfer of the user data to the work volume is performed toward an address in the user volume corresponding to an address in the user volume. Method. 9. The backup acquisition method according to claim 6, wherein the transfer of the user data to the work volume includes a process of storing an address of an area of the work volume to which the user data has been transferred. .