JP2868015B1 - Disk storage system - Google Patents

Abstract

Kind Code: A1 A plurality of read requests to a storage device group are efficiently executed. A control device sends a first read request and a second read request to different storage devices in a storage device group,
Execute using different paths and different external connection points.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a storage device,
The present invention relates to a disk storage system for distributing a load to be executed.

[0002]

2. Description of the Related Art Japanese Patent Application Laid-Open No. Sho 60-114947 discloses a technique relating to a dual writing function of a disk device in a control device having a disk cache (hereinafter, sometimes simply referred to as a cache). Here, two disk devices to which the same data is written are referred to as a double-write disk.

Japanese Patent Application Laid-Open No. Sho 60-114947 describes a method for controlling a write data double (two) disk device using a disk cache as follows. The control device processes an input / output request from the CPU to one of the two disk devices. When a read request (input request) is received,
The control device executes the received request as it is. CPU
When a write request (output request) is received from the server, the following processing is executed. That is, while writing data to one of the dual-write disks,
This data is also written in the disk cache.
Then, the control device later writes the data written in the disk cache to the other disk device using the vacant time. This writing process is called a write after process. As described above, the same data is written to the double-write disk device.

Japanese Patent Publication No. 28128/1986 discloses a technique relating to load balancing of a dual-write disk device as a method of controlling a duplicate file. Tokiko Sho 61-2812
No. 8 aims to speed up the processing by selecting a free disk device when processing an input / output request. However, JP-B-61-28128 is disclosed in
As in -114947, a method of writing data twice by write-after control using a disk cache is not used.

Nishigaki et al .: Effect analysis of disk cache in sequential access input processing, Transactions of Information Processing Society of Japan, V
ol. 25, no. 2, pp. 313-320 (198
In the paper 4), the following technology is disclosed.
This is a technique for prefetching a sequential process in a control device having a disk cache, that is, a technique in which data not requested by the CPU is staged in the cache. This stage processing is executed by the control device independently of responding to an input / output request from the CPU.

[0006]

Problems to be Solved by the Invention JP-A-60-1149
No. 47 does not pay attention to the advantage that there are a plurality of disk devices that can be processed by the control device in a dual-write disk. That is, the number of disk devices to be selected in response to an input / output request received from the CPU is limited to a specific one.

On the other hand, as disclosed in JP-B-61-28128, a method of selecting a vacant disk device in response to an input / output request is excellent in performance. However, if this method is applied to a case where a double writing function is realized by write-after control using a cache, the reliability is deteriorated. This is because there is a high possibility that there is post-write data received from CPUs corresponding to all disk devices. Therefore, if the cache power-down and the failure of any one disk device overlap, the write data received from the CPU will be lost.

Further, in the case of a control device having a cache, the control device executes input / output processing between the cache and the disk device independently of an input / output request received from the CPU. (This is Nishigaki et al .: Effect Analysis of Disk Cache in Sequential Access Input Processing, Transactions of Information Processing Society of Japan, Vol. 25, No. 2, pp. 313-320.
(1984). Therefore, it should be noted that there are a plurality of disk devices that can be selected as an object to which the input / output processing is executed independently of the input / output processing from the CPU by the control device. .

The present invention relates to a control method and a control device for writing the same data to a disk device group including one or more disk devices by a write after process using a cache.

An object of the present invention is to provide a control device and a control method for distributing the load of I / O processing to be executed between disk devices in a disk device group and improving the parallelism of execution of I / O processing. Is to do.

[0011]

In order to make the description of the method and apparatus for solving the problem easier to understand, the input / output processing executed by the control device with respect to the disk device is classified.

The input / output processing executed by the control device with the disk device can be classified into the following four types.

(1) Processing for a write request received from the CPU, which requires access to the disk device.

(2) Processing for a read request received from the CPU, which requires access to the disk device.

(3) A stage process for transferring data from the disk device to the cache, independent of an input / output request (read request / write request) from the CPU.

(4) Write-after processing executed with the disk device.

Of the above input / output processing, the write-after processing is not a target of load distribution. Hereinafter, the reason will be described. The write-after process is a process executed when executing a write request received from the CPU for all disk devices in a disk device group other than the disk device to which data has been written. For this reason, there is no flexibility in selecting a disk device on which the write-after process is to be performed. Therefore, among the processes (1) to (4), the processes (1) to (3) are subject to load distribution.

In this specification, two types of methods for performing load distribution will be described. For convenience, these methods are referred to as load distribution method 1 and load distribution method 2. Hereinafter, each method will be described.

Load distribution method 1 ... The control device is as described in (2) above.
Alternatively, when selecting a disk device for which the input / output processing of (3) is to be executed, an arbitrary empty disk device in the disk device group is selected. When selecting a disk device in response to the write request received from the CPU that needs to access the disk device in (1) above, a specific disk device in the disk device group is selected.

Load distribution method 2... The control device responds to the above-described processing category (1), that is, the write request received from the CPU which needs to access the disk device,
When selecting a disk device, a specific disk device in the disk device group is selected. When selecting a disk device to be subjected to the input / output processing shown in the processing classification (2) or (3), a disk device other than the specific disk device is preferentially selected.

The operation corresponding to each of the load distribution method 1 and the load distribution method 2 will be described.

(1) In the case of the load distribution method 1, the control device issues a read request for accessing a disk device to a certain disk device group by the CPU.
, The following processing is executed. In response to the read request, any one free disk device in the disk device group is selected. If there is no empty disk device, the control device waits for the read request. When a write request that needs to access a disk device is received, one specific disk device in the disk device group is selected in response to the write request. However, if the specific disk device is not empty, the control device waits for the write request.

Also, when the control device attempts to execute a stage process independent of an input / output request from the CPU, the following process is performed. That is, one free disk device in the disk device group is selected in correspondence with this stage processing. If there is no empty disk device, the control device does not execute the stage processing.

The reliability and performance characteristics of the load distribution method 1 are described below.

The load distribution method 1 is disclosed in Japanese Unexamined Patent Publication No. 60-1149.
47, the dispersion effect is slightly inferior, but superior performance can be obtained as compared with the method disclosed in JP-B-61-28128.

Hereinafter, the reason will be described. Load distribution method 1
Means that the degree of freedom in selecting a disk device for a write request is limited. Therefore, Japanese Patent Application Laid-Open
The effect of dispersion will be inferior to the method disclosed in 114947. However, in response to a read request, an empty disk device is selected. Normally, the ratio of input / output requests to the disk device is considerably higher in read requests than in write requests. (3: 1 to 4: 1
Therefore, load distribution method 1 is disclosed in
Compared to the method disclosed in No. 14947, no significant performance degradation occurs. On the other hand, all input / output requests are concentrated on one disk device.
Compared with the method of No. 28, the load distribution method 1 can obtain excellent performance.

The reliability of the load distribution method 1 is disclosed in
The method is higher than the method disclosed in Japanese Patent No. 114947, and is substantially equivalent to the method disclosed in JP-B-61-28128.

Hereinafter, the reason will be described. According to the load distribution method 1 or Japanese Patent Publication No. 61-28128, there is no data to be subjected to write-after processing for a disk device that concentrates write requests. Therefore, even if the power of the cache goes down, the write data received from the CPU does not disappear unless a failure occurs in the disk device that concentrates the write requests.

As described above, according to the load distribution method 1, it is possible to perform load distribution that achieves high performance / reliability of a disk device group in a well-balanced manner.

(2) In the case of load distribution method 2 When the controller receives a write request from the CPU which needs to access a disk device in the disk device group, the controller responds to the write request and responds to the write request. One of the disk devices is selected. However, if the specific disk device is not empty, the control device waits for the write request. When a read request for accessing a disk device of a certain disk device group is received from the CPU, the following process is executed. First, an arbitrary free disk device is selected from disk devices other than the specific disk device. When there is no empty disk device, it is checked whether or not the specific disk device is empty. If so, the controller selects this particular disk device for the received read request. If not, the control device waits for the read request.

Also, when the control device attempts to execute a stage process independent of an input / output request from the CPU, the following process is performed. First, an arbitrary one of the disk devices other than the above-described specific disk device in an empty state is selected. If there is no empty disk device, it is checked whether or not the specific disk device is empty. If free, the control unit:
This particular disk device is selected for the stage processing to be performed. If not, the control device does not execute the stage processing.

The reasons for using the above-mentioned dispersion method are as follows. For example, assume that a process corresponding to a read request is assigned to a specific disk device that concentrates a process corresponding to a write request from the CPU. In this case, if a write request is received before the process corresponding to the read request is completed, the process will not be performed in response to the write request. Therefore, for processing other than processing corresponding to a write request from the CPU that does not need to select a specific disk device, it is better to preferentially allocate a disk device other than this specific disk device to increase the effect of dispersion. can do.

[0033]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, two types of embodiments of the present invention will be described. First, contents common to both embodiments will be described.

FIG. 2 shows the configuration of a computer system to which the present invention is applied. The computer system has a CPU 20
0, a main memory 201, and a channel 202, a control device 203, and one or more n disk devices 204. The control device 203
It will be apparent from the following description that the present invention can be applied to a case where a plurality of processing devices 210 are connected.

Each of the n disk devices 204 has one
It is grouped into m disk device groups 211 including at least two disk devices 204. The number of disk devices 204 belonging to each disk device group 211 may be different. Each disk device 2
04 belongs to one disk device group 211. The method of determining which disk device group 211 each disk device 204 belongs to is not directly related to the present invention, and thus the description is omitted.

The control device 203 includes one or more directors 205, a cache (memory) 206, a control information memory 207, and a directory 208. Each director 205 has a channel 202 and a disk device 2
04, between the channel 202 and the cache 206, and between the cache 206 and the disk device 204.
Transfer data between and. In the cache 206, data frequently accessed among the data stored in the disk device 204 is staged. The directory 208 stores management information of the cache 206. The stage processing is executed by the director 205.
Specific examples of the stage data include data to be accessed by the CPU 20 and data in which the storage position of the disk device 204 is close to the data.

The control device 203 to which the present invention is applied is a disk device 2 belonging to a certain disk device group 211.
04 has a function of writing the same data, that is, a so-called multiple writing function. Therefore, it may be considered that the processing device 210 issues an I / O request to each disk device group 211.

In the present invention, when viewed from the control device 203, the input / output requests received from the processing device 204 can be classified as follows.

(1) Cache 206 and processing unit 210
This is an input / output processing pattern in which the disk device group 211 is not accessed. This is a processing pattern that is executed, for example, when data corresponding to a read request received from the processing device 210 is staged in the cache 206.

(2) An input / output processing pattern that requires access to the disk device 204 in the disk device group 211.

(3) Further, when the control device 203 has the cache 206, the control device 203 executes the following input / output processing independently of the input / output request received from the processing device 210.

This is an input / output processing pattern between the cache 206 and the disk devices 204 in the disk device group 211, and is a data transfer pattern that does not involve the processing device 210.

According to the present invention, the same disk device group 2
11 relates to a method of distributing the load among the disk devices 204 belonging to 11. Therefore, the processing pattern that does not need to access the disk device group 211 shown in (1) is
It will not be directly related to the present invention. Control device 20
The input / output processing patterns shown in (2) and (3) out of the input / output processing patterns executed by No. 3 are the objects of the present invention. Note that the disk device 204 to which the input / output processing shown in (2) or (3) is not assigned (the processing is not being executed) is referred to as an empty disk device.

The outlines of the two embodiments will be described below. First, an outline of the first embodiment will be described.

FIG. 1 is a diagram for explaining the operation of the control device 203 in the first embodiment.

In the configuration of FIG. 1, one master disk A, B, and C exists in each of the disk device groups A, B, and C. The difference between the master disk and other disk devices will be described later. The master disk is a specific disk device predetermined in each disk device group.

In FIG. 1, the disk device group A
The disk device group B and the disk device group C are connected to the control device 203.

The disk device group A includes a master disk A, disks A1,..., Disk Ai. Similarly, the disk device group B is composed of master disks B,..., Disks Bj, and the disk device group C is composed of master disks C,.

The input / output requests received by the control unit 203 from the processing unit 210 and needing to access the disk unit group 211 will be described separately for write requests and read requests. In FIG. 1, the data flow accompanying a write request is indicated by reference numeral 110, and the data flow accompanying a read request is indicated by reference numeral 113. Hereinafter, a data transfer pattern for each request will be described.

The control device 203 has received a write request 110 that needs to access the disk device group A. The control device 203 controls the disk device group A
, The master disk A is selected. That is, the master disk A is a disk device that concentrates write requests that need to access the disk device group A.

The control device 203 writes the data accompanying the write request received from the processing device 210 to the master disk A and also writes the data to the cache 206. The control device 203 executes the same data write processing on the disk devices belonging to the same disk device group, for example, the master disk A, the disk devices A1,..., The disk device Ai. The write data 111 written in the cache 206 is used to execute the above-described write processing. The details will be described later.

When a write request requiring access to the disk device group A is received, the reason for selecting the master disk A is as follows. If a write request that needs to access the disk device group A is always assigned to the master disk A, the entire write data 112 received from the processing device 210 is written to the master disk A. For this reason, for example, even when a disk Ai other than the master disk A fails and the cache 206 is powered down,
Complete data is held in the master disk A.

However, since the degree of freedom in selecting a disk device is limited to the allocation of the write request received from the processing device 210, the performance is reduced. In particular,
When the control device 203 receives the write request 110 that needs to access the disk device group A, even if the disk A1 other than the master disk A is free,
If the master disk A is not empty, the processing cannot be immediately started.

FIG. 1 also shows a case where the control device 203 has received a read request that requires access to the disk device processing group C. At this time, the control device 20
No. 3 selects one disk device (disk C1 in FIG. 1) from any empty disk devices in the disk device group C.

The control device 203 sends the requested data from the disk C1 to the processing device 210. (This path is indicated by reference numeral 113.) At this time, the data requested by the processing device 210 (or the data requested by the processing device 210 and the data near the disk C1 of the data) is set as the stage data 114 and cached. 206
May be staged. This is indicated by a broken line.

The input / output processing between the disk unit group and the cache 206 executed by the control unit 203 independently of the input / output request received from the processing unit 210 is shown in FIG.
There is the following processing shown in FIG. Write-after processing for writing write data to the disk device is a stage process independent of input / output requests from the processing device 210. An example of a stage process independent of the processing device 210 corresponds to a case where the control device 203 executes a prefetch process for a sequential process. Hereinafter, each case will be described.

The write-after process is a process of writing the write data 111 in the cache 206 to the unwritten disk device Ai. In the disk device group A, it is not necessary to execute the write-after process on the master disk A to which the write data 111 received from the processing device 210 is directly written. Therefore, write-after processing is sequentially performed on disks A1,..., And disk Ai except master disk A. The order of execution may be random.

When executing a stage process independent of the processing device 210 for a certain disk device group B, the control device 203 determines that any one of the disk devices in the disk device group B is free. Select In FIG. 1, the control device 203 has staged the stage data 116 in the cache 206 from the disk Bj.

The above is the description of the control device 203 in this embodiment.
Operation. The features are as follows.

For a write request that needs to access a disk device group received from the processing device 210, a master disk is selected to ensure reliability. On the other hand, when reading data from a disk device group,
Select an empty disk unit. As described above, high reliability and high performance are realized in a well-balanced manner.

Hereinafter, an example of the parallel operation will be described with reference to FIGS.

FIG. 3 shows an embodiment in which the control device 203 executes the following pattern of input / output processing in parallel.

The input / output processing of the first pattern is an input / output processing which needs to access the disk device group A received from the processing device 210.

The input / output processing of the second pattern is an input / output processing executed by the control unit 203 with the cache 206 independently of the processing unit 210.

For example, as shown in FIG.
3 performs stage processing independent of input / output processing from the processing device 210 with the disk A1, and write-after processing with the disk A2. At this time, it is assumed that the control device 203 further receives an I / O request that requires access to the disk device group A from the processing device 210. FIG. 3 shows an example in which a read request requiring access to the disk device group A is received. In this case, the control device 203 can start execution of the received I / O request by selecting an empty disk device Ai from the disk device group A.
However, the input / output request received from the processing device 210 is
In the case of a write request that requires access to the disk device group A, the same processing cannot be executed unless the master disk A is free.

In FIG. 3, each of the write after process and the stage process independent of the processing device 210 are executed one by one. However, if there is an empty disk device, the control device 203 can execute two or more multiplex write-after processes and a stage process independent of the processing device 210.

FIGS. 4 and 5 show the contents relating to the parallel operation of the input / output processing received from the processing device 210. FIG.

FIG. 4 shows a processing unit 210
, Specifically, the processing device 210 and the processing device 210
a is connected.

It is assumed that the control device 203 is executing a read request received from the processing device 210 and required to access the disk device group A, with the disk A1. At this time, it is assumed that the control device 203 has received a read request that requires access to the disk device group A from the processing device 210a. The control device 203 selects an empty disk device in the disk device group A, that is, a disk Ai, and starts processing of the received read request. Of course, even when a write request that needs to access the disk device group A is received from the processing device 210a, if there is an empty disk device, the process can be immediately started. However, due to contention of the master disk A, a parallel operation of write requests that need to access the disk device group A cannot be executed.

Further, three or more processing units are connected to the control unit 2.
In the case where it is connected to 03, if there is only an empty disk device, I / O requests that need to access three or more disk device groups A can be executed in parallel.

FIG. 5 shows a processing unit 210
Are connected. The processing device 210
It is assumed that the system has a function of issuing a new I / O request to the disk device group A before the processing for the I / O request to the disk device group A is completed.

In FIG. 5, the control unit 203 performs the processing of a read request received from the processing unit 210, which needs to access the disk unit group A, on the disk A1.
Suppose you are running between In this state, the control device 2
03 receives a read request from the processing device 210 that further needs to access the disk device group A. The control device 203 selects an empty disk device in the disk device group A, that is, a disk Ai, and starts processing of the received read request. Of course, even when a write request that needs to access the disk device group A is received from the processing device 210, if there is an empty disk device, the process can be immediately started. However, due to the contention of the master disk A, a parallel operation of write requests that need to access the disk device group A cannot be executed.

Further, even when the processing device 210 issues an I / O request of three or more multiplexes to the same disk device group A, the control device 203 is issued as long as there is an empty disk device. I / O requests can be executed in parallel.

The above is the outline of the first embodiment. Next, an outline of the second embodiment will be described.

FIG. 6 shows an outline of the second embodiment.

The second embodiment differs from the first embodiment in the operation of the control device 203 in the following points. For a read request that needs to access a disk device group, a disk device other than the master disk is preferentially selected. Similarly, for stage processing independent of the processing device 210, a disk device other than the master disk is preferentially selected. The reason for using the method described above is that
If you select a disk device other than the master disk,
This is because the speed can be further increased. I mean,
This is because when a write request that needs to access the disk device group is received, the probability that the master disk is free can be increased.

Hereinafter, details of the embodiment will be described.

First, the first embodiment will be described in detail.

The configuration of the computer system shown in FIG.
The embodiment can be applied as it is. Hereinafter, each of them will be described in detail.

FIG. 8 shows the configuration of the disk device 204. The disk 801 is a medium for recording data, and is a plurality of rotating bodies in one disk device 204.
The read / write head 802 is a device that reads and writes data on the disk 801, and exists for the disk 308. The control device interface 803 is an interface with the control device 203.

A circular recording unit accessible by the read / write head 802 while the disk 801 makes one rotation is called a track 800. A plurality of tracks 800 exist on the disk 801.

FIG. 9 shows the configuration of the track 800. For the track 800, a track start 902 and a track end 903 are determined based on a certain position. One or more records 900 exist on the track 800. The record 900 includes the processing device 210 and the control device 20.
3 is the minimum input / output processing unit. Truck 80
The position of the record 900 on 0 is expressed in units of a fixed length byte called a cell 901. (The record 900 always starts to be stored from the beginning of the cell 901 and does not start to be stored in the middle of the cell 901.) The number of the cell 901 is assigned in ascending order by 1 with the beginning of the track 800 being 0.

FIG. 10 shows the configuration of the cache 206. The cache 206 includes a segment 1000. In this embodiment, one track 800 corresponds to one.
One segment 1000
It is assumed that data of the entire track 800 is stored in 0. However, in the present invention, the allocation unit of the segment 1000 does not need to be limited to the track 800, but may be a smaller unit, for example, the processing device 210 and the control device 203.
Is also effective as a record 900 which is a read / write unit between the two.

FIG. 11 shows the structure of the directory 208. The directory 208 stores the segment management information 110
0, a track slip 1101, and a free segment head pointer 1102. The segment management information 1100 exists in units of 1000 segments.
Track slip 1101 and empty segment pointer 11
02 exists in the control device 203.

FIG. 12 shows information required in this embodiment in the segment management information 1100. Hereinafter, each parameter and its contents are shown.

Empty segment pointer 1200: A pointer to segment management information 1100 corresponding to another segment 1000 not allocated to the track 800.

Cached track number 1201... Segment 400 corresponding to segment management information 500
Represents the number of the disk device group 211 and the number of the track 800 stored in the storage area.

Record bitmap 1202... Represents the start position of the record 900 on the track 800 stored in the segment 400 corresponding to the segment management information 500. Here, it is assumed that each bit exists in correspondence with the number of the cell 901. For example, if the n-th bit in the record bitmap 1202 is on,
The storage of the record 301 has been started from the n-th cell 901 corresponding to the segment management information 1100. If the n-th bit is off, there is no record 301 whose storage has been started from the n-th cell 901. FIG. 13 shows a storage format on the track 800 in the segment 1000 in this embodiment. The segment 1000 includes a record 90 from the track head 901 on the track 800.
0s are stored in order. Therefore, if the number of the cell 901 to be stored on the track of the record 900 is known, the storage start position in the segment 1000 of the record 301 can be known.

Update record bitmap 1203: segment 400 corresponding to the segment management information 500
Is a bitmap of a record 900 that is stored in the file and that needs the write-after processing 112. The record 900 requiring the write process 112 is hereinafter referred to as a write after record. Each bit exists in correspondence with the number of the cell 901 similarly to the record bitmap 1202. Specifically, if the n-th bit in the update record bitmap 1203 is ON, the record 301 whose storage is started from the n-th cell 901 corresponding to the segment management information 1100 is called a write-after record. Will be. Update record bitmap 120
No. 3 exists for one disk device 204. More specifically, the correspondence between the update bitmaps 1203 and the disk devices 204 will be described in the description of the configuration of the control memory 207. The area of the update record bitmap 1203 is prepared by the number of the definable disk devices 204 in one disk device group 211. However, the number of update record bitmaps 1203 used is the number of disk devices 204 that make up the disk device group.

Stored flag 1204: Indicates whether the record 900 on the allocated track 800 is stored in the segment 1000 corresponding to the segment management information.

In use flag 1205: Indicates that the input / output processing corresponding to the track 800 assigned to the segment management information 1100 is being executed.

Segment pointer 1206... A pointer to the segment 1000 corresponding to the segment management information.

FIG. 14 shows the configuration of the track slip 1101 and the free segment head pointer 1102.

The track slip 1101 indicates whether or not the segment 800 is assigned to the track 800 of all the disk device groups 211. If assigned, it indicates a pointer to the segment management information 1200 corresponding to the segment 1000 assigned to the track 800. In the track slip 1201, information on the tracks 800 on the same disk device group 211 is collectively stored in the track 800 number order.

The segment management information 1100 corresponding to the segment 1000 to which the track 800 has not been allocated includes:
The free segment pointers 1200 are joined in order from the free segment head pointer 1102. A set of segment management information 1100 that is combined is referred to as an empty segment queue 1400.

FIG. 15 shows the configuration of the control information memory 207. The control information memory 207 includes disk device group information 1500 which is control information corresponding to each disk device group 211. The number of disk device group information 1500 is equal to the number of disk device groups 211 that can be defined in one control device 203.

FIG. 16 shows the disk device group information 15
00 configuration.

Disk device number 1600: The number of disk devices 204 currently defined in the disk device group 211.

Disk device information 1601... Information corresponding to each disk device 204 constituting the disk device group information 1500. Disk device information 16
00, only the disk devices 204 that can be defined in one disk device group 211 are prepared. However, valid information is stored from the first disk device information 1601 to the number of disk device information 1601 defined in the number 1600 of disk devices. Here, the head disk device information 1601 is information corresponding to the master disk.

Also, n in the segment management information 1200
The update record bitmap 1203 of the disk device 20 corresponding to the n-th disk device information 1601
4.

Processing device I / O wait bit 1602... This bit indicates that an input / output request received from the processing device 210 to the disk device group 211 is in a waiting state. The number of these bits can be expressed as follows: number of processing device I / O wait bits 1602 = control device 20
3 (here, I) × the number of I / O processing requests that one processor 210 can process in parallel for one disk device group 210 Here, the number of processing units is J.) Therefore, when each processing device 210 issues an input / output request to the control device 203, the processing device 210 notifies the control device 203 of the following two points. First, the first point is that the number of the processing device 210 from the first to the I-th is the processing device 210 that issues the input / output request. The second point is that the number of the I / O request from the first to the J-th is notified to the specified disk device group 211.

FIG. 17 shows the structure of the disk device information 1601.

Disk device number 1700: The number of the disk device 204 corresponding to the disk device information 1700.

Processing device I / O executing bit 1701... Disk device 2 corresponding to the disk device information 1700
04 indicates by 1 bit that the input / output request from the processing device 210 is being executed.

Write after execution bit 1702... Disk device 20 corresponding to the disk device information 1700
4 indicates that the write-after process 112 is being executed.
Expressed in bits.

Independent stage executing bit 1703: Disk device 20 corresponding to the disk device information 1700
4 is a stage process 115 independent of the processing device 210
Is indicated by 1 bit.

At most one of the processing device I / O execution bit 1701, write after execution bit 1702, and independent stage execution bit 1703 is turned on at the same time. Also, the processing device I / O execution bit 170
The disk device 204 in which the write-after-execution bit 1702 and the independent-stage-execution bit 1703 are all off is the disk device 204 in an empty state.

Segment management information pointer 1704... Disk device 2 corresponding to the disk device information 1700
Track 80 accessed by the input / output processing being executed in 04
Indicates a pointer to the segment management information 1100 assigned to “0”.

Since there is a problem if the information in the control information memory 207 is lost due to a power failure or the like, it is desirable that the control information memory 207 be nonvolatile.

The input / output processing to be executed by the control device 203 is actually executed by the respective directors 205 in the control device 203 in parallel.

FIG. 18 shows each director 205
However, each procedure used when executing this embodiment is shown.
Hereinafter, each function will be described.

Input / output request receiving unit 1800: Processes input / output requests received from the processing unit 210.

Write-after processing schedule section 1801
... Schedule the light-after processing.

Independent stage processing schedule section 1802
... Schedule stage processing independent of the processing device 210.

Disk device transfer section 1803: A portion for executing read / write transfer with the disk device 204.

FIG. 19 shows an input / output request receiving unit 1800.
It is a processing flow figure of. Input / output request receiving unit 1800
Is executed when a new input / output request is received from the processing device 210. Hereinafter, the processing flow will be described.

In step 1900, it is checked whether the received I / O request is an I / O request that needs to access the disk device 204. The details of what input / output requests need to access the disk device 204 are not directly related to the present invention, and thus the details are omitted. If the received input / output request does not require access to the disk device 204, the process jumps to step 1915.

The processing after step 1901 is a processing in the case where the received input / output request is an input / output request that needs to access the disk device 204.

In step 1901, the track 300 to be accessed by the input / output request is
Check if is being allocated. If you are allocating, step 1
Jump to 903.

In step 1902, the segment management information 1 is assigned to the track 300 to be accessed by the input / output request.
100 is assigned and linked to the corresponding area of the track slip 1101. Further, the allocated segment management information 11
The stored flag 1205 of 00 is turned off, and the in-use flag is turned on. At this time, the segment management information 1100 to be allocated includes an empty segment head queue 1102.
The segment management information 1100 which is in an empty state is selected. Segment management information 1100 in an empty state
If there is no segment management information, the currently allocated segment management information is selected by a known method. The specific selection method is not related to the present invention, and thus the description is omitted. Thereafter, the process jumps to step 1905.

In step 1903, it is checked whether the busy flag 1205 of the segment management information 1100 being allocated to the track 300 to be accessed by the input / output request is on. If it is on, it means that the track 300 to be accessed by another input / output process is currently being used. Therefore, the received input / output request is not immediately executed, so that the process jumps to step 1914.

If the in-use flag 1205 is off, the in-use flag 1205 is turned on in step 1904.

Next, at step 1905, it is checked whether the input / output request is a read request or a write request. In the present invention,
A write request that needs to access the disk device group 211 causes the master disk to be accessed. Therefore, if the input / output request is a read request, step 1
Branch to 908.

In the case of a write request, at step 1906,
Check if the master disk is free.
This check checks the following information in the disk device information 1601 corresponding to the master disk in the disk device group 211 to be input / output (that is, the first disk device information 1601 in the disk device group information 1500). To check. That is, the processing device I /
O executing bit 1701, write after executing bit 1
702, it is checked whether all bits of the independent stage execution bit 1703 are off (whether they are vacant). If the master disk is empty,
In step 1907, the master disk is selected as an access target. Specifically, the processing device I / O execution bit 1701 in the disk device information 1601 corresponding to the master disk is turned on. When the above process is completed, the process jumps to step 1910 and enters the same process as in the first embodiment.

If the master disk is not empty,
In order to put the input / output request in a waiting state, step 191 is executed.
Jump to 3.

In step 1908, the disk device 20
The disk device 204 is allocated to the read request that needs to access the disk device 204. In this embodiment, an arbitrary free disk device is assigned to a read request that needs to be accessed by the disk device 204. Therefore, the vacant disk device 20 is included in the disk device group 211 to be input / output.
Check if 4 is available. The specific processing contents are as follows. That is, the disk device information 1601 in which all bits of the processing device I / O execution bit 1701, the write after execution bit 1702, and the independent stage execution bit 1703 are turned off is found. If not found, there is no empty disk device 204,
The process jumps to step 1913 because it cannot enter the input / output processing.

If found, in step 1909, the disk unit number 17 in the disk unit information 1601 is displayed.
The disk device 204 corresponding to 00 is selected as an access target. Specifically, the found disk device information 1
A processing device I / O execution bit 1701 in the 601 is turned on.

Further, in step 1910, a pointer to the segment management information 1100 assigned to the track 800 to be accessed by the input / output request is set in the segment management information pointer 1704.

At step 1911, step 1909 is executed.
A positioning process request is issued to the disk device 204 selected in step.

In step 1912, the disk device 20
Until the positioning process of No. 4 is completed, once the processing device 21
The processing for disconnecting the connection relationship with 0 is executed with the processing device 210. Thereafter, the processing of the input / output request receiving unit 1800 is terminated.

If there is no empty disk device 204, the following processing is executed in and after step 1913.

At step 1913, the in-use flag 1205 of the corresponding segment management information 1100 is turned off.

Thereafter, in step 1914, it is checked whether the stored flag 1204 is on. If it is on, jump to step 1916. When off, the segment 100 corresponding to the segment management information 1100
In step 1915, this segment management information is registered in the empty segment queue 1400 in order to indicate that no data is contained in 0.

Further, at step 1916, the processing device 2
10, the processing request I / O wait bit 1602 in the disk device group information 1500 is set to indicate that the processing for the input / output request has not been executed for another input / output processing. Specifically, the position of the processing request I / O wait bit 1602 to be set is determined from the following two points, and the bit is set.

First, the first point is the number of the processing device 210 from the first to the I-th which has issued the input / output request.

Next, the second point is how many I / O requests from No. 1 to J to the specified disk device group 210.

When the segment management information 1100 of the track 800 to be accessed by the input / output request is used by another input / output processing, it is not necessary to operate the information in the segment management information 1100 in particular. Therefore, the process jumps to step 1916.

Finally, at step 1917, the processing device 2
10 reports that the process corresponding to the input / output request enters a wait state because it cannot be executed for another input / output process. Thereafter, the processing of the input / output request receiving unit 1800 is terminated.

In step 1918, the disk device 20
4 is executed for an input / output request that does not need to access the program. The specific processing content is
Since the present invention is not directly related, the description is omitted.

FIG. 20 is a processing flow of the write-after processing schedule section 1801. The write-after processing schedule unit 1801 executes the process using the time when the director 25 is idle.

In step 2000, a disk device group 210 to be written-after is determined. Since this determination method has no direct relation to the present invention, the description is omitted.

In step 2001, an empty disk device to be input / output is found in the determined disk device group other than the master disk. The specific processing contents are as follows. That is, other than the master disk, the processing device I / O execution bit 170
The disk device information 1601 in which all bits of the write-after-execution bit 1702 and the independent-stage execution bit 1703 are turned off is found. If not found, the write-after processing cannot be executed, so the processing of the write-after processing schedule section 1801 is terminated.

If found, in step 2002, the write-after-execution bit 1702 in the disk device information 1601 found in step 2001 is turned on.

At step 2003, step 2001
And write-after processing 11 to the disk device 204
2 checks whether there is a track 800 that can be executed. The specific check information is the track slip 1101
, The segment management information 1100 having an ON bit in the update record bitmap 1203 corresponding to the selected disk device 204 is searched. Further, since it is necessary that another processing request is not being used for the segment management information, the fact that the in-use flag 1205 in the segment management information 1100 is off is also a condition under which the write-after processing can be executed. If found, step 2
Jump to 005. If there is no track 800 on which the write-after process can be executed, the write-after-execution bit 1702 is turned off in step 2004. After this,
The processing of the write-after processing schedule unit 1801 ends.

In step 2005, a track 800 to be subjected to write-after processing is selected. When there are a plurality of tracks 800 on which the write-after process can be executed, which track 800 to select is not related to the present invention, and therefore, the description is omitted.

In step 2006, step 2005
Turns on the in-use flag 1205 in the segment management information 1100 corresponding to the track 800 selected in step.

In step 2007, the segment management information pointer 1704 stores the segment management information 1 assigned to the track 800 to be accessed by the input / output request.
Set a pointer to 100.

In step 2008, step 2001
A positioning process request is issued to the disk device 204 selected in step. Thereafter, the processing of the write-after processing schedule unit 1801 is terminated.

FIG. 21 is a processing flow of the independent stage processing schedule section 1802. The independent stage processing schedule unit 1802 also executes using the time when the director 25 is idle.

In step 2100, a disk device group 210 to execute the stage processing 115 independent of the processing device 210 is determined. This determination method is not directly related to the present invention, similarly to step 2000, and therefore, the description is omitted.

In step 2101, step 2100
In the disk device group 211 found in the above, the track 8 for which stage processing independent of the processing device 210 is to be executed
Check if there is 00. Since this checking method is not directly related to the present invention, the description is omitted. If there is no track 800 to be executed, the processing of the independent stage processing schedule section 1802 is terminated.

At step 2102, a track 800 to be subjected to stage processing independent of the processing device 210 is selected. When there are a plurality of tracks 800 capable of performing the stage processing independent of the processing device 210, which track 800 is selected is not relevant to the present invention. Therefore, the description is omitted.

In step 2103, step 2004
To the track 800, the segment management information 11
Assign 00. (The track 800 on which the stage processing 115 independent of the processing device 210 is to be executed is a track 800 that has not been staged in the cache 206.) This allocation method is as described in step 1902. Further, the allocated segment management information 11
In 00, the stored flag 1204 is turned off and the busy flag 1205 is turned on.

In step 2104, step 2100
In the disk device group determined in step 2, an empty disk device to be an input / output target is found. The specific processing content is the same as that of step 1908, and thus the description is omitted. If not found, the stage processing 115 independent of the processing device 210 cannot be executed. Therefore,
In step 2105, the assigned segment management information 1
100 to the free segment queue 1400. Thereafter, the processing of the independent stage processing schedule section 1802 is ended.

If found, in step 2106, the independent stage executing bit 1702 in the disk device information 1601 found in step 2103 is turned on.

In step 2107, the segment management information pointer 1704 stores the segment management information 1 assigned to the track 800 to be accessed by the input / output request.
Set a pointer to 100.

At step 2108, step 2001
A positioning process request is issued to the disk device 204 selected in step. Thereafter, the processing of the independent stage processing schedule section 1802 is terminated.

FIG. 22 is a processing flowchart of the disk device transfer unit 1803. The timing of execution of the disk device transfer unit 1803 is when the director 205 receives the positioning completion report of the disk device 204.

In step 2200, the segment management information 1100 pointed to by the segment management information pointer 1704 in the disk device information 1601 corresponding to the disk device 204 is selected as a processing target. Less than,
When simply describing the segment management information 1100, the segment management information 1100 selected in step 2200
Point to. Further, when the information in the segment management information 1100 is simply indicated, it indicates the information in the segment management information 1100 selected in step 2200.

In step 2201, it is checked whether the processing device I / O execution bit 1701 in the disk device information 1601 corresponding to the disk device 204 is on. If it is off, the process jumps to step 2212 to indicate that the currently executing input / output process is not a process for the input / output request received from the processing device 210.

When the processing device I / O execution bit 1701 is on, the input / output processing being executed
Indicates that this is a process for the input / output request received from. Therefore, in step 2202, the processing device 210
Reports that the positioning process has been completed, and returns to the connected state.

In step 2203, it is determined whether the input / output request received from the processing device is a read request or a write request. In the case of a read request, the process jumps to step 2209.

In the case of a write request, in step 2204,
The data received from the processing device 204 is divided into the disk device 204 and the segment management information 1 selected as the processing target.
Write to the segment 1000 corresponding to 100. At this time, it is necessary to recognize the number of the cell 901 of the record 800 on the disk device 204 to which the data has actually been written, and perform the following processing. First, data to be written in the segment 1000 is also written to a position corresponding to the recognized cell 901. Further, the following processing is performed on the update record bitmap 1203 corresponding to all the disk devices 204 other than the master disk in the segment management information 1100 selected as the processing target. That is, the bit corresponding to the number of the cell 901 recognized in the update record bitmap 1203 is turned on. Further, the completion of the input / output processing is reported to the post-processing device 210.

In step 2205, the stored flag 120 in the segment management information 1100 to be processed is set.
Check if 4 is on. If it is ON, the record 900 on the track 300 to be processed is staged in the segment 1000.
Jump to 15.

If the stored flag 1204 is off, the record 900 on the track 300 to be processed is
It will not be staged in segment 1000. Therefore, the following processing is performed after step 2206. In step 2206, the bit position of the record bitmap 1202 corresponding to the number of the cell 901 recognized in step 2204 is turned on.

Next, at step 2207, the remaining records 900 of the track 800 being processed are
The processing to be staged in 00 is executed. Also in this case, it is necessary to recognize the number of the cell 901 of the record 900 to be staged and perform the following processing. First, the record 900 to be staged in the segment 1000 is also written at a position corresponding to the recognized cell 901. Further, the bit position of the record bitmap 1202 corresponding to the number of the recognized cell 901 is turned on. Thereafter, in step 2208, the stored flag 1204 is turned on, and the process jumps to step 2215.

In step 2209 and subsequent steps, the processing device 21
Processing of the read request accepted from 0 is performed.

In step 2209, it is checked whether the stored flag 1204 in the segment management information 1100 to be processed is on. When the stored flag 1204 is ON, the record 900 has already been stored in the segment 1000. Therefore, the record 900 requested in step 2210 is sent from the disk device 204 to the processing device 210. Thereafter, the completion of the input / output processing is reported to the processing device 210. Next, step 221
Jump to 5.

When the stored flag 1204 is off, the record 900 on the track 300 to be processed during processing is not staged in the segment 1000. Therefore, the following processing is performed after step 2211. First, in step 2210, the requested record 900 is sent from the disk device 204 to the processing device 210, and is also staged in the segment 1000. Also in this case, the cell 9 of the record 900 targeted for the stage
It is necessary to recognize the number 01 and perform the following processing. First, a record 90 to be staged in the segment 1000
0 is also written to the position corresponding to the recognized cell 901. Further, in the record bitmap 1202 in the segment management information 1100 selected as the processing target,
The bit corresponding to the number of the recognized cell 901 is turned on. Thereafter, the completion of the input / output request is reported to the processing device 210. Next, the track 30 to be processed
Jump to step 2207 to stage the remaining records 900 on 0.

In step 2212, it is checked whether the write-after-execution bit 1702 in the disk device information 1601 corresponding to the disk device 204 is on. If it is off, the process jumps to step 2214 to execute the stage processing 115 independent of the processing device 210.

At step 2213, all write-after records are recognized by the update record bitmap 1203 in the segment management information 1100 to be processed. Further, all recognized write-after records are written on the disk device 204. Thereafter, the update record bitmap 1203 corresponding to the disk device 204 is all cleared to zero. Next, step 22
Jump to 15.

In step 2214, a stage process independent of the processing device 210 is executed. Specifically, all records 90 on the track 800 to be processed
Stage 0 in segment 1000. Also in this case, it is necessary to recognize the number of the cell 901 of the record 900 to be staged and perform the following processing. First, the record 900 to be staged in the segment 1000 is also written at a position corresponding to the recognized cell 901. Further, the following processing is performed on the record bitmap 1202 in the segment management information 1100 to be processed. That is, the bit position of the record bitmap 1202 corresponding to the number of the recognized cell 901 is turned on. In addition, the stored flag 1204 is turned on.

In step 2215 and subsequent steps, the following processing is performed as termination processing.

First, in step 2215, the in-use flag 1 in the segment management information 1100 is to be processed.
Turn off 205. Next, in step 2216, the disk device information 16 corresponding to the disk device 204
01, all bits of the processing device I / O execution bit 1701, the write after execution bit 1702, and the independent stage execution bit 1703 are turned off.

Finally, in step 2217, the following processing is performed to release the waiting state of the I / O request for which the processing request I / O waiting bit 1602 corresponding to the disk device group 211 to be processed is on. I do. That is, the waiting state of all the input / output requests determined by the processing devices 210 from No. 1 to I and the input / output numbers from No. 1 to J are released from the ON bit. Specifically, the respective processing devices are again notified to issue those input / output requests. Thereafter, the processing of the disk device transfer unit 1802 ends.

Next, a second embodiment will be described. The differences between the second embodiment and the first embodiment are as follows.

A read request that needs to access the disk device group 211 and a stage process independent of the processing device 210 are performed by the disk device 20 other than the master disk.
4 is selected with priority.

In the first embodiment, the respective data structures shown in FIGS. 8 to 17 can be used as they are in the second embodiment.

The configuration of the modules required to execute the first embodiment in the director 205 shown in FIG. 18 can be applied to the third embodiment as it is. However, regarding the processing flow of each module, the input / output request receiving unit 1800 and the independent stage processing scheduling unit 1802 are slightly different from those in the first embodiment. However, the processing flow of the first embodiment can be applied as it is to the processing flows of other modules.

FIG. 23 is a processing flow of the input / output request receiving unit 1800 in the third embodiment. The timing of execution of the input / output request receiving unit 1800 is the same as in the first embodiment.

Hereinafter, differences between the processing flow of the first embodiment shown in FIG. 19 and the processing flow of FIG. 23 will be described. In the processing flow of FIG. 23, the steps having the same processing contents as those of the processing flow of FIG. 19 have the same step numbers. The difference between FIG. 23 and the processing flow of FIG. 19 is that step 2300 is included instead of step 1908 of FIG.

At step 2300, it is preferentially selected whether a disk device 204 other than the master disk is empty. This is because the second embodiment preferentially selects a disk device 204 other than a read request and a master disk that needs to access the disk device group 211. Specifically, the following information in the disk device information 1601 of the disk device 204 other than the master disk is checked. That is, the processing device I / O execution bit 1701, the write after execution bit 1702,
It is checked whether all bits of the independent stage executing bit 1703 are off.

If there is an empty disk device 204, the process jumps to step 1909 to select the disk device 204 as an access target, and enters the same processing as the processing flow of FIG. If there is no free disk drive 204, check the free space of the master disk.
The process jumps to step 1906 and enters the same processing as the processing flow of FIG.

Except for the following points, the processing flow of FIG. 23 and the nineteenth processing flow are exactly the same, and therefore description thereof will be omitted.

FIG. 7 is a processing flow of the independent stage processing schedule section 1802 in the second embodiment. The execution timing of the independent stage processing schedule unit 1802 is:
This is the same as in the first embodiment.

Hereinafter, differences between the processing flow of the first embodiment shown in FIG. 21 and the processing flow of FIG. 7 will be described. Note that, in the processing flow of FIG. 7, the steps having the same processing contents as those of the processing flow of FIG. 21 have the same step numbers.

The processing flow shown in FIG. 7 is different from the processing flow shown in FIG.
The point different from the processing flow in the embodiment is as follows.

First, after finding the empty disk device 204 after step 2102, the second embodiment differs from the second embodiment in that an empty disk device 204 other than the master disk is found in step 2400. This is because the second embodiment preferentially selects a disk device 204 other than the master disk 120 in the stage processing independent of the processing device 210. The specific processing content is the same as that of step 2300, and thus the description is omitted.

If there is an empty disk device 204, the process jumps to step 2104 to select the disk device 204 as a disk to be accessed, and enters the same processing as in the first embodiment.

Disk device 204 other than master disk
If is not empty, it is checked in step 2401 whether the master disk is empty. The above processing is the same as the processing in step 1906, and thus the description is omitted. If the master disk is free, in step 2402, the master disk is selected as an access target. Specifically, the processing device I / O execution bit 17 in the disk device information 1601 corresponding to the master disk
Turn on 01. Thereafter, the process jumps to step 2107 and enters the same processing as in the first embodiment.

When the master disk is not empty, stage processing independent of the processing device 210 cannot be executed.
Therefore, the process jumps to step 2105 and enters the same processing as in the first embodiment. Except for the points described above, the processing flow of FIG. 7 and the twenty-first processing flow are completely the same, and thus the description is omitted.

[0192]

According to the present invention, a high performance / high reliability of a control device having a cache having a function of writing the same data to a disk device group including one or more disk devices can be realized in a well-balanced manner. This is because, according to the present invention, the input / output processing can be distributed among the disk devices within a range that does not impair the reliability, and the parallelism of the input / output processing that can be executed by the control device can be improved.

[Brief description of the drawings]

FIG. 1 shows a control device 203 according to a first embodiment of the present invention.
This is the basic operation of.

FIG. 2 is a configuration of a computer system to which the present invention is applied.

FIG. 3 shows an input / output request received from a processing device 210;
The input / output request from the processing device 210 means the control device 203
Represents the parallel operation of the input / output processing executed independently.

FIG. 4 illustrates a parallel operation of a plurality of input / output requests received from a plurality of processing devices 210.

FIG. 5 illustrates a parallel operation of a plurality of input / output requests received from one processing device 210.

FIG. 6 illustrates a control device 203 according to a second embodiment of the present invention.
This is the basic operation of.

FIG. 7 shows a processing flow chart of an independent stage schedule processing unit 1802 in the second embodiment.

FIG. 8 shows a configuration of a disk device 24.

FIG. 9 shows a configuration of a track 800.

FIG. 10 shows a configuration of a cache 206.

FIG. 11 shows information necessary for the present invention in a directory 208.

FIG. 12 shows information necessary for the present invention in the segment management information 1100.

FIG. 13 shows a configuration of a track slip 1101 and a free segment queue head pointer 1102.

FIG. 14 shows a storage format of a record 901 on a track 800 in a segment 1000.

FIG. 15 shows information stored on a control memory 207.

FIG. 16 shows a configuration of disk device group information 1500.

FIG. 17 shows a configuration of disk device information 1601.

FIG. 18 illustrates modules within director 205 related to the present invention.

FIG. 19 shows a processing flowchart of the input / output request receiving unit 1800.

FIG. 20 shows a processing flowchart of the write-after-schedule processing unit 1801.

FIG. 21 shows a processing flowchart of the independent stage schedule processing unit 1802.

FIG. 22 shows a processing flowchart of the disk device read / write processing unit 1803.

FIG. 23 illustrates a processing flowchart of an input / output request receiving unit 1800 in the second embodiment.

[Explanation of symbols]

203: control device, 210: processing device, 211: disk device group, 110: write request, 113: read request, 112: write after process, 115: stage process, 120: master disk.

──────────────────────────────────────────────────の Continued on the front page (72) Inventor Yoshihiro Azumi 2880 Kozu, Kozuhara, Odawara City, Kanagawa Prefecture Inside the Hitachi, Ltd.Odawara Plant (72) Inventor Yoshiyoshi Kuwahara 2880 Kozu, Kozu, Odawara, Kanagawa Prefecture Inside the Hitachi Ltd.Odawara Plant (72) Inventor Hiroyuki Kitajima 1099 Ozenji Temple, Aso-ku, Kawasaki City, Kanagawa Prefecture, Hitachi Systems Development Laboratory Co., Ltd. (56) References JP-A-58-219656 (JP, A) U) Tokuho Sho 61-28128 (JP, B2) (58) Fields investigated (Int. Cl. ⁶ , DB name) G06F 3/06-3/08

Claims (3)

(57) [Claims] 1. A control device having a plurality of external connection points, a storage device group composed of a plurality of storage devices, and write data being written to each storage device, each of which is connected to the storage device group and the control device. A disk storage system comprising a plurality of paths to be executed, wherein the control device receives first and second read requests for the storage device group, and stores data requested by the first read request. First reading from any one storage device connected by any one of the plurality of paths in the storage device group
And a second read operation for reading data requested by the second read request from another storage device connected by another one of the plurality of paths in the storage device group. A first transfer operation of transferring the data read in the first read operation to any one of the plurality of external connection points;
Performing a second transfer operation of transferring the data read by the read operation to another one of the plurality of external connection points. 2. The method according to claim 1, wherein the first and second read requests are issued from a processing device to the storage device group, and wherein the control device reads the data read in the first read operation. Transferring the data read by the second read operation to the processing device via the one external connection point, and transferring the data read by the second read operation to the processing device via the another external connection point. Item 2. The disk storage system according to item 1. 3. The control device includes a first external connection point connectable to a first processing device, and a second external connection point connectable to a second processing device. Receiving the first read request issued from the first processing device and the second read request issued from the second processing device, wherein the processing device performs the first read operation Is transferred to the first processing device via the first external connection point, and the data read in the second read operation is transferred to the second processing device in the second processing device. 2. The disk storage system according to claim 1, wherein the data is transferred via an external connection point.