JP2008234264A - Load balancing device for file server, program for load balancing, and load balancing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To distribute load among file servers even if the file servers are full in capacity in a storage system including a file server group. <P>SOLUTION: The load balancing device 300 is provided between a client 100 and a storage system 200. The load balancing device 300, when detecting connection of a new file server 201d to file servers 201a-201c, performs first file relocation so that load is distributed among the file servers 201a-201d including the file server 201d, and clears out the file server 201d, after completion of the first file relocation, and performs second file relocation so that the load is distributed within the original file servers 201a-201c. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a load distribution device for a file server, a program for the load distribution device, and a load distribution method, and more particularly to a load distribution device for a file server, a program for the load distribution device, and a load distribution in a load distribution system involving attachment / detachment of a file server. Regarding the method.

  In a storage system such as NAS (Network Attached Storage) in which the entire file server group (cluster) in the network is a single virtual file server, if data with a high access load is unevenly distributed to some file servers, the file server group There is a problem that access performance as a whole deteriorates.

  In order to solve such a problem, conventionally, a load distribution technique has been devised that prevents uneven access load of each file server in the network and improves the access performance of the entire file server group.

  For example, in Patent Document 1, in a file storage management system having a plurality of storage devices on a network, by monitoring the tendency of access requests for each file on the storage device and dynamically changing the file arrangement, A system for preventing uneven access load and speeding up file access is disclosed.

JP-A-10-320261

However, the above-described conventional load distribution technique has a problem that it is difficult to distribute the access load because the file cannot be moved between the file servers when the capacity of each file server is not sufficient.
(Object of invention)
An object of the present invention is a load distribution device for a file server, a program for the load distribution device, which solves the problem that the access load cannot be distributed when the capacity of the file server is not sufficient, which is the above-described conventional problem, And providing a load balancing method.

  The first load distribution apparatus of the present invention monitors file access to a plurality of file servers in a storage system and stores an access load for each file in an access load storage unit, and to the storage system Monitoring means for detecting the connection of the additional file server, and when the connection of the additional file server is detected by the plug monitoring means, a plurality of files excluding the additional file server based on the contents of the access load storage means The file is selected from the file server so that the access load among all the file servers in the storage system is distributed, and the first file is relocated to be moved to the additional file server. After the file rearrangement, the file moved to the additional file server is added to the additional file server. File relocation means for performing second file relocation that selects and moves a file server as a migration destination from the plurality of file servers so that the access load among the plurality of file servers excluding the file server is distributed And.

  According to a second load distribution apparatus of the present invention, in the first load distribution apparatus, when the file relocation unit detects connection of the additional file server by the plug monitoring unit, the file storage unit stores the file storage unit in the mode storage unit. When the mode related to the file relocation operation is the addition mode, only the first file relocation is performed. When the mode is the temporary addition mode, the first file relocation and the second file relocation are performed. It is characterized by performing.

  According to a third load distribution apparatus of the present invention, in the second load distribution apparatus, when the file relocation unit is instructed by the client to an empty creation mode in which the file server to be deleted is designated, the access load storage unit Based on the contents, the file server to be moved from the file server to be deleted so that the access load among the plurality of file servers excluding the file server to be deleted is distributed. It is characterized by selecting and moving.

  The first load distribution device program of the present invention comprises: an access load monitoring unit that monitors a file access to a plurality of file servers in a storage system and stores an access load for each file in an access load storage unit; A plug monitoring unit for detecting connection of the additional file server to the storage system; and when the connection of the additional file server is detected by the plug monitoring unit, the additional file is based on the contents of the access load storage unit. Select a file from a plurality of file servers excluding servers so that the access load among all the file servers in the storage system is distributed, and perform the first file relocation to move to the additional file server After the first file relocation, the additional file server In order to distribute the access load among the plurality of file servers excluding the additional file server, the second file re-transferring the moved file by selecting the file server as the destination from the plurality of file servers. It is characterized by functioning as a file relocation means for performing the arrangement.

  According to a second load distribution device program of the present invention, in the first load distribution device program, when the file relocation unit detects the connection of the additional file server by the plug monitoring unit, the mode storage unit When the mode relating to the file relocation operation stored in the file is the addition mode, only the first file relocation is performed. When the mode is the temporary addition mode, the first file relocation and the second file relocation operation are performed. The file relocation is performed.

  According to a third load balancer program of the present invention, in the second load balancer program, when the file relocation unit is instructed by a client to an empty creation mode designating a file server to be deleted, the access Based on the contents of the load storage means, the file of the deletion target file server is moved from the deletion target file server so that the access load among the plurality of file servers excluding the deletion target file server is distributed. A file server to be selected is selected and moved.

  According to a first load distribution method of the present invention, an access load monitoring step in which a load distribution apparatus monitors file access to a plurality of file servers in a storage system and stores an access load for each file in an access load storage unit; A plug monitoring step for detecting connection of an additional file server to the storage system, and when the connection of the additional file server is detected by the plug monitoring step, the additional file is determined based on the contents of the access load storage means. Select a file from a plurality of file servers excluding servers so that the access load among all the file servers in the storage system is distributed, and perform the first file relocation to move to the additional file server After the first file relocation, the additional file server In order to distribute the access load among the plurality of file servers excluding the additional file server, the second file re-transferring the moved file by selecting the file server as the destination from the plurality of file servers. And a file rearrangement step for performing the arrangement.

  According to a second load distribution method of the present invention, in the first load distribution method, the file rearrangement step is stored in a mode storage unit when the connection of the additional file server is detected by the plug monitoring step. When the mode related to the file relocation operation is the addition mode, only the first file relocation is performed. When the mode is the temporary addition mode, the first file relocation and the second file relocation are performed. It is characterized by performing.

  According to a third load distribution method of the present invention, in the second load distribution method, when the file relocation step is instructed by the client to an empty creation mode in which the file server to be deleted is designated, the access load storage means Based on the contents, the file server to be moved from the file server to be deleted so that the access load among the plurality of file servers excluding the file server to be deleted is distributed. It is characterized by selecting and moving.

  The effect of the present invention is that, in a storage system composed of a group of file servers composed of a plurality of file servers connected by a network, load distribution is performed among the file servers even if the capacity of each file server is not sufficient. It can be done.

  The reason is that when the load balancer detects a new file server connection as a trigger, the first file relocation is performed so that the load is distributed including that file server. This is because when the placement is completed, the second file is rearranged so that the file in the file server is emptied and the load is distributed in the original file server group.

  Next, the best mode for carrying out the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows a configuration of a load distribution system according to an embodiment of the present invention. Referring to FIG. 1, the load distribution system according to the embodiment of the present invention includes a client 100, a storage system 200, and a load distribution apparatus 300. The client 100 and the load balancer 300, and the storage system 200 and the load balancer 300 are connected to each other via a network. Here, the client 100 is a device on the user side of the storage system 200. The storage system 200 connects a plurality of file servers 201 via a network and provides a virtual file server as a whole. The file server 201 is a server on which a storage device 202 having a fixed storage medium is mounted, and performs access such as reading / writing data on the storage device 202 in accordance with a request from the client 100.

  The load distribution apparatus 300 is an access point when the client 100 uses the file server 201, and performs access load distribution through file access load monitoring and file relocation. The load distribution apparatus 300 is an information processing apparatus that operates under program control, and includes a mode designation execution unit 301, an access load monitoring unit 302, a file server load calculation unit 303, a plug monitoring unit 304, an event processing unit 305, and a file rearrangement unit. 306, a file access control unit 307, a mode storage unit 351, an access load storage unit 352, a file server load storage unit 353, a plug state storage unit 354, and a file location storage unit 355.

  Here, the mode storage unit 351 stores and manages the mode designated by the user regarding the file rearrangement operation when the file server 201 is connected or disconnected. As shown in FIG. 9, the access load storage unit 352 stores and manages the access load for each file. As the access load, the number of accesses per unit time (access frequency) and the data transfer amount can be used. The file server load storage unit 353 stores and manages access load information for each file server 201 as shown in FIG. The plug status storage unit 354 stores and manages the connection status of the file server 201 recognized in the storage system 200, as shown in FIG. As shown in FIG. 12, the file location storage unit 355 stores and manages the location (which file server 201 is present) for each file.

  The mode designation execution unit 301 accepts a mode (“addition mode”, “temporary addition mode”) related to the file relocation operation when the file server 201 is connected from the user, and stores it in the mode storage unit 351. Also, a request for removal preparation operation (“empty creation mode”) is received from the user and notified to the event processing unit 305.

  The access load monitoring unit 302 constantly monitors each file, acquires the access load for each file, and updates the contents of the access load storage unit 352.

  The file server load calculation unit 303 calculates the access load for each file server 201 with reference to the contents of the access load storage unit 352 and updates the contents of the file server load storage unit 353.

  The plug monitoring unit 304 constantly monitors the physical connection state of the file server 201 to the storage system 200, and updates the contents of the plug state storage unit 354 when a new connection or disconnection event of the file server 201 occurs. To do. Further, when a connection event of the file server 201 occurs, the event processing unit 305 is notified immediately.

  When the event processing unit 305 receives a notification of the connection event of the file server 201 from the plug monitoring unit 304 or receives a notification of the preparation operation from the mode designation execution unit 301, the event processing unit 305 and the plug status storage The execution content of the file relocation unit 306 is determined with reference to the unit 354, and the file relocation unit 306 is instructed to execute the file relocation.

  The file rearrangement unit 306 moves and rearranges files between the file servers 201 based on an instruction from the event processing unit 305. Further, the contents of the file location storage unit 355 are updated according to the location of the file after the rearrangement.

  The file access control unit 307 refers to the file location storage unit 355 when performing data access in response to a request from the client 100, determines which file server 201 in the storage system 200 has data, and accesses the data I do.

  Next, the operation of the embodiment of the present invention will be described with reference to the drawings.

  In the embodiment of the present invention, three modes of “addition mode”, “empty creation mode”, and “temporary addition mode” are used as modes stored in the mode storage unit 351. The “addition mode” is for adding the file server 201 to the storage system 200 to perform load distribution. As shown in FIG. 2, when an empty file server 201 is added to the storage system 200, it is automatically added. The files are rearranged so that the access load is distributed among all the file servers 201 including the file server 201 that has been changed. The “free server creation mode” is used as a preparation for detaching the file server 201 from the storage system 200. As shown in FIG. 3, the file rearrangement is performed so that the file server 201 designated by the user is empty. I do. In the “temporary addition mode”, when the capacity of the file server 201 in the storage system 200 is not sufficient, the access load is distributed using the temporarily added free file server 201. FIG. As shown, when an empty file server 201 is added, the files are automatically rearranged so that the access load is distributed among all the file servers 201 including the added file server 201. In addition, the files are rearranged again so that the added file server 201 becomes empty. Hereinafter, the operation in each mode will be described in detail.

"Additional mode"
FIG. 5 shows an operation flow of the “addition mode”. Here, a case where an empty file server 201d is added to the file servers 201a to 201c on the storage system 200 will be described as an example.

  The access load monitoring unit 302 monitors file access of each file server 201 in the storage system 200 and records access load information and statistics in the access load storage unit 352 for each file. However, file access related to file relocation executed for load distribution is not counted in the access load statistics.

  The mode designation execution unit 301 receives the designation of “additional mode” by the user from the client 100 in advance (step S101). The mode designation execution unit 301 stores the designated mode in the mode storage unit 351 (step S102).

  When the file server 201d is added to the storage system 200, the plug monitoring unit 304 detects the connection of the file server 201d, adds the file server 201d to the plug state storage unit 354 (step S103), and adds it to the event processing unit 305. The connection of the file server 201d is notified (step S104).

  The event processing unit 305 confirms the “additional mode” from the contents of the mode storage unit 351 (step S105). The event processing unit 305 refers to the plug state storage unit 354, confirms that the file server 201d exists, accesses the file server 201d, and confirms that the file server 201d is empty (step S106). The event processing unit 305 instructs the file server load calculation unit 303 to calculate the load of each file server 201 (step S107).

  The file server load calculation unit 303 refers to the access load storage unit 352 and the file location storage unit 355, acquires the access load for each file, aggregates the files for each file server 201, and records them in the file server load storage unit 353 ( Step S108).

  The event processing unit 305 designates the file server 201d and instructs the file relocation unit 306 to perform file relocation (file relocation from the file servers 201a to 201c to the file server 201d) accompanying the connection of the file server 201. (Step S109).

  The file relocation unit 306 determines a file to be moved from the file servers 201a to 201c to the added file server 201d based on the contents of the access load storage unit 352 and the file server load storage unit 353 (step S110). The file to be moved to the file server 201d is selected so that the access loads of the moved file servers 201a to 201d are distributed. The file rearrangement unit 306 moves the selected file from the file servers 201a to 201c to the file server 201d (step S111). The file rearrangement unit 306 updates the file location storage unit 355 according to the location of the file after the rearrangement (step S112).

  When the movement is completed, the event processing unit 305 notifies the client 100 of the movement completion through the mode designation execution unit 301 (steps S114 and S115).

  When there is a request for data access from the client 100, the file access control unit 307 refers to the file location storage unit 355, determines which file server 201 in the storage system 200 has the data, and Access.

"Empty creation mode"
FIG. 6 shows an operation flow of the “empty creation mode”. Here, a case where the file server 201d is removed from the file servers 201a to 201d on the storage system 200 will be described as an example.

  The mode designation execution unit 301 receives designation of the “empty creation mode” by the user from the client 100 together with information on the file server 201 to be removed (file server 201d) (step S201). The mode designation execution unit 301 saves the designated mode in the mode storage unit 351, and notifies the event processing unit 305 that “empty creation mode” has been designated (step S202).

  The event processing unit 305 refers to the plug state storage unit 354, confirms that the designated file server 201d exists, accesses the file server 201d, and confirms that the file server 201d is not empty (step S203). ). The event processing unit 305 instructs the file server load calculation unit 303 to calculate the load of each file server 201 (step S204).

  The file server load calculation unit 303 refers to the access load storage unit 352 and the file location storage unit 355, acquires the access load for each file, aggregates the files for each file server 201, and records them in the file server load storage unit 353 ( Step S205).

  The event processing unit 305 designates the file server 201d and performs the file rearrangement (the file server 201d is emptied and the file servers 201a to 201c are rearranged) when the file server 201 is disconnected. (Step S206).

  Based on the contents of the access load storage unit 352 and the file server load storage unit 353, the file relocation unit 306 determines the destination file servers 201a to 201c for all the files of the file server 201d (step S207). The migration destination of the file in the file server 201d is selected so that the access load of the migrated file servers 201a to 201c is distributed. Here, when the file to be relocated exceeds the capacity limit of the transfer destination file servers 201a to 201c, the file relocation unit 306 determines that the transfer is not possible because the capacity of the transfer destination file system is exceeded. The client 100 may be notified through the processing unit 305 and the mode designation execution unit 301. The file rearrangement unit 306 moves the file from the file server 201d to the file servers 201a to 201c according to the selected destination (step S208). The file rearrangement unit 306 updates the file location storage unit 355 according to the location of the file after the rearrangement (step S209).

  When the movement is completed, the event processing unit 305 notifies the client 100 of the movement completion through the mode designation execution unit 301 (steps S211 and S212).

  When the file server 201d is removed from the storage system 200, the plug monitoring unit 304 detects the disconnection of the file server 201d, and deletes the file server 201d from the plug state storage unit 354 (step S213).

"Temporary addition mode"
7 and 8 show an operation flow of the “temporary addition mode”. Here, a case where an empty file server 201d is temporarily added to the file servers 201a to 201c on the storage system 200 will be described as an example.

  The mode designation execution unit 301 accepts the designation of “temporary addition mode” by the user from the client 100 in advance (step S301). The mode designation execution unit 301 stores the designated mode in the mode storage unit 351 (step S302).

  When the file server 201d is added to the storage system 200, the plug monitoring unit 304 detects the connection of the file server 201d, adds the file server 201d to the plug state storage unit 354 (step S303), and sends it to the event processing unit 305. The connection of the file server 201d is notified (step S304).

  The event processing unit 305 confirms the “temporary addition mode” from the contents of the mode storage unit 351 (step S305). The event processing unit 305 refers to the plug state storage unit 354, confirms that the file server 201d exists, accesses the file server 201d, and confirms that the file server 201d is empty (step S306). The event processing unit 305 instructs the file server load calculation unit 303 to calculate the load of each file server 201 (step S307).

  The file server load calculation unit 303 refers to the access load storage unit 352 and the file location storage unit 355, acquires the access load for each file, aggregates the files for each file server 201, and records them in the file server load storage unit 353 ( Step S308).

  The event processing unit 305 designates the file server 201d and instructs the file relocation unit 306 to perform file relocation (file relocation from the file servers 201a to 201c to the file server 201d) accompanying the connection of the file server 201. (Step S309).

  The file relocation unit 306 determines a file to be moved from the file servers 201a to 201c to the added file server 201d based on the contents of the access load storage unit 352 and the file server load storage unit 353 (step S310). The file to be moved to the file server 201d is selected so that the access loads of the moved file servers 201a to 201d are distributed. The file rearrangement unit 306 moves the selected file from the file servers 201a to 201c to the file server 201d (step S311). The file rearrangement unit 306 updates the file location storage unit 355 according to the location of the file after the rearrangement (step S312).

  When the movement is completed, the event processing unit 305 instructs the file server load calculation unit 303 to calculate the load of each file server 201 again (step S314).

  The file server load calculation unit 303 refers to the access load storage unit 352 and the file location storage unit 355, acquires the access load for each file, aggregates the files for each file server 201, and records them in the file server load storage unit 353 ( Step S315).

  The event processing unit 305 designates the file server 201d and performs file relocation (empty the file server 201d and file relocation by the file servers 201a to 201c) when the file server 201 is disconnected. Is instructed to the file rearrangement unit 306 (step S316).

  Based on the contents of the access load storage unit 352 and the file server load storage unit 353, the file relocation unit 306 determines the destination file servers 201a to 201c for all the files of the file server 201d (step S317). The migration destination of the file in the file server 201d is selected so that the access load of the migrated file servers 201a to 201c is distributed. The file relocation unit 306 moves the file from the file server 201d to the file servers 201a to 201c according to the selected movement destination (step S318). The file rearrangement unit 306 updates the file location storage unit 355 according to the location of the file after the rearrangement (step S319).

  When the movement is completed, the event processing unit 305 notifies the client 100 of the movement completion through the mode designation execution unit 301 (steps S321 and S322).

  When the file server 201d is removed from the storage system 200, the plug monitoring unit 304 detects the disconnection of the file server 201d and deletes the file server 201d from the plug state storage unit 354 (step S323).

  Thus, the operation of the embodiment of the present invention is completed.

  According to the embodiment of the present invention, in a storage system configured by a file server group composed of a plurality of file servers connected by a network, even when there is no room for each file server, the file servers Can perform load balancing.

  The reason is that when the load balancer detects a new file server connection as a trigger, the first file relocation is performed so that the load is distributed including that file server. This is because when the placement is completed, the second file is rearranged so that the file in the file server is emptied and the load is distributed in the original file server group.

  Further, according to the embodiment of the present invention, in a storage system composed of a file server group composed of a plurality of file servers connected by a network, load distribution by adding file servers or temporary addition of file servers The user can easily execute the load distribution according to. The reason is that the user sets an operation mode for determining the operation when a file server connection is detected for the load balancer, and the load balancer enters the operation mode triggered by the detection of a new file server connection. In response to the first file rearrangement including load distribution including the file server, or in addition to the first file rearrangement, empty the file in the file server to the original file server This is because the second file relocation is performed so that the load is distributed within the group.

  The present invention can be applied to a cluster-type file server system using a network in which a file server group or a database server group is regarded as a virtual file server. Further, the present invention can be applied in a wide range from a small file server system to a large capacity file server system represented by music distribution, video on demand, etc., regardless of the scale of the storage system.

It is a block diagram which shows embodiment of this invention. It is a figure which shows the outline of operation | movement of the "addition mode" in embodiment of this invention. It is a figure which shows the outline of operation | movement of the "empty creation mode" in embodiment of this invention. It is a figure which shows the outline of operation | movement of the "temporary addition mode" in embodiment of this invention. It is a flowchart which shows operation | movement of the "additional mode" in embodiment of this invention. It is a flowchart which shows operation | movement of the "empty creation mode" in embodiment of this invention. It is a flowchart which shows operation | movement of the "temporary addition mode" in embodiment of this invention. It is a flowchart which shows the operation | movement (continuation of FIG. 7) of the "temporary addition mode" in embodiment of this invention. In embodiment of this invention, it is a figure which shows the content which an access load memory | storage part carries out memory management. In embodiment of this invention, it is a figure which shows the content which a file server load memory | storage part carries out memory management. In embodiment of this invention, it is a figure which shows the content which a plug state memory | storage part manages and manages. In embodiment of this invention, it is a figure which shows the content which a file location memory | storage part stores and manages.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Client 200 Storage system 201 File server 202 Storage apparatus 300 Load distribution apparatus 301 Mode designation execution part 302 Access load monitoring part 303 File server load calculation part 304 Plug monitoring part 305 Event processing part 306 File rearrangement part 307 File access control part 351 Mode storage unit 352 Access load storage unit 353 File server load storage unit 354 Plug status storage unit 355 File location storage unit

Claims (9)

An access load monitoring unit that monitors file access to a plurality of file servers in the storage system and stores an access load for each file in an access load storage unit;
Plug monitoring means for detecting connection of an additional file server to the storage system;
When connection of the additional file server is detected by the plug monitoring means, all file servers in the storage system are selected from a plurality of file servers excluding the additional file server based on the contents of the access load storage means. The file is selected so that the access load between the files is distributed, the first file is relocated to the additional file server, and the file is moved to the additional file server after the first file relocation is completed. In order to distribute the access load among the plurality of file servers excluding the additional file server, the second file rearrangement is performed by selecting and moving the file server as the migration destination from the plurality of file servers. File relocation means;
A load balancer comprising: When the plug monitoring unit detects the connection of the additional file server, and when the mode relating to the file relocation operation stored in the mode storage unit is the addition mode, the file relocation unit is configured to perform the first file relocation. When only the placement is performed and the mode is the temporary addition mode, the first file rearrangement and the second file rearrangement are performed.
The load distribution apparatus according to claim 1. When the file relocation unit is instructed by the client to be in an empty creation mode in which a deletion target file server is specified, the file relocation unit converts the file of the deletion target file server into the deletion target file server based on the contents of the access load storage unit. Select and move the destination file server from the file server to be deleted so that the access load among multiple file servers excluding
The load distribution apparatus according to claim 2. Computer
An access load monitoring unit that monitors file access to a plurality of file servers in the storage system and stores an access load for each file in an access load storage unit;
Plug monitoring means for detecting connection of an additional file server to the storage system;
When connection of the additional file server is detected by the plug monitoring means, all file servers in the storage system are selected from a plurality of file servers excluding the additional file server based on the contents of the access load storage means. The file is selected so that the access load between the files is distributed, the first file is relocated to the additional file server, and the file is moved to the additional file server after the first file relocation is completed. In order to distribute the access load among the plurality of file servers excluding the additional file server, the second file rearrangement is performed by selecting and moving the file server as the migration destination from the plurality of file servers. File relocation means;
A program for a load balancer characterized in that the program is made to function. When the plug monitoring unit detects the connection of the additional file server, and when the mode relating to the file relocation operation stored in the mode storage unit is the addition mode, the file relocation unit is configured to perform the first file relocation. When only the placement is performed and the mode is the temporary addition mode, the first file rearrangement and the second file rearrangement are performed.
The program for a load balancer according to claim 4. When the file relocation unit is instructed by the client to be in an empty creation mode in which a deletion target file server is specified, the file relocation unit converts the file of the deletion target file server into the deletion target file server based on the contents of the access load storage unit. Select and move the destination file server from the file server to be deleted so that the access load among multiple file servers excluding
The program for a load balancer according to claim 5. The load balancer
An access load monitoring step of monitoring file access to a plurality of file servers in the storage system and storing an access load for each file in an access load storage means;
A plug monitoring step of detecting connection of an additional file server to the storage system;
When connection of the additional file server is detected by the plug monitoring step, all file servers in the storage system are selected from a plurality of file servers excluding the additional file server based on the contents of the access load storage means. The file is selected so that the access load between the files is distributed, the first file is relocated to the additional file server, and the file is moved to the additional file server after the first file relocation is completed. In order to distribute the access load among the plurality of file servers excluding the additional file server, the second file rearrangement is performed by selecting and moving the file server as the migration destination from the plurality of file servers. A file relocation step;
A load balancing method comprising: In the file rearrangement step, when the plug monitoring step detects the connection of the additional file server, when the mode related to the file rearrangement operation stored in the mode storage means is the addition mode, the first file relocation step is performed. When only the placement is performed and the mode is the temporary addition mode, the first file rearrangement and the second file rearrangement are performed.
The load distribution method according to claim 7. In the file rearrangement step, when an empty creation mode designating a deletion target file server is instructed from a client, the file of the deletion target file server is changed to the deletion target file server based on the contents of the access load storage means. Select and move the destination file server from the file server to be deleted so that the access load among multiple file servers excluding
9. The load distribution method according to claim 8, wherein:

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