Patent Publication Number: US-2015089129-A1

Title: Computer system and storage management method

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS 
     This application is a Continuation of U.S. application Ser. No. 13/263,285 (National Stage of PCT/JP2011/005355), filed Oct. 6, 2011, incorporated herein by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a computer system and a storage management method and is suited for use in, for example, a computer system and storage management method for dynamically allocating storage areas. 
     BACKGROUND ART 
     Recently, an amount of data dealt by a computer system has been increasing explosively. Along with an increase of the data amount, it is necessary to purchase new volumes as needed and add the volumes to a storage apparatus. The storage apparatus manages a plurality of hard disk drives (HDDs) by means of a RAID (Redundant Arrays of Independent/Inexpensive Disks) system. Then, the storage apparatus logicalizes physical storage areas of the plurality of hard disk drives and provides them as logical volumes to a host computer. The host computer accesses the provided logical volumes and requests reading/writing of data. 
     There is a function called Thin Provisioning as one of methods for providing logical volumes to a host computer. The thin provisioning function is a function providing virtualized logical volumes which do not have physical storage areas (hereinafter referred to as virtual volumes), to the host computer, and dynamically allocating the storage areas to the virtual volumes as triggered by write access by the host computer to the virtual volumes. The above-described thin provisioning function has the advantage that the virtual volumes of a larger capacity than that of storage areas, which can be actually provided, can be provided to the host computer and an inexpensive computer system can be configured by reducing the physical storage capacity, which should be prepared in advance, in a storage apparatus. 
     Furthermore, a method for managing each storage area provided by each of a plurality of kinds of storage media with different performance, which are mounted in a storage apparatus, as a plurality of kinds of different storage tiereds is suggested as a data management method for the storage apparatus equipped with the above-described thin provisioning function. Also, a technique called dynamic tiered control to migrate data in a storage tiered according to access frequency from the host computer is suggested. For example, storage areas are allocated from a high-speed and high-performance storage tier to an area where data with high access frequency is stored; and storage areas are allocated from a low-speed and low-performance storage tier to an area of the virtual volumes where data with low access frequency is stored. Furthermore, Patent Literature 1 discloses a technique of sorting data according to performance requirements and allocating storage areas of a high-performance storage tier to an area where data of a high performance requirement is stored. 
     If the above-described dynamic tiered control technique is used, cost performance for the storage apparatus can be enhanced. Accordingly, data stored in normal logical volumes are often managed by migrating such data to a storage tiered. Therefore, a sizing tool for calculating the structure of an appropriate storage tiered in accordance with a performance request from a user is provided. 
     CITATION LIST 
     Patent Literature 
     [PTL 1] 
     Japanese Patent Application Laid-Open (Kokai) Publication No. 2007-66259 
     SUMMARY OF INVENTION 
     Technical Problem 
     However, since Patent Literature 1 calculates the structure of a storage tiered by using a predefined combination of storage media, it sometimes results in a higher-cost structure than a case where storage media actually retained by the user are used. Furthermore, the structure of the storage tiered calculated by using the predefined combination of the storage media may sometimes include storage media, which are not actually retained by the user, or have a capacity shortage even if the storage media are retained by the user, so that the requested storage tiered cannot be created. In this case, it is necessary to purchase new storage media to replenish the storage media which are not retained by the user or to overcome the capacity shortage in order to realize the calculated structure of the storage tiered. So, the problem is that the storage media retained by the user cannot be utilized effectively. 
     The present invention was devised in consideration of the above-described circumstances and aims at suggesting a computer system and storage management method capable of recognizing the type and capacity of storage media of a storage apparatus, which are held by a user, and configuring a storage tiered that satisfies desired performance by using the storage media. 
     Solution to Problem 
     In order to solve the above-described problems, a computer system including a storage apparatus, a host computer requesting writing of data to the storage apparatus, and a management computer for managing the storage apparatus and the host computer, wherein the storage apparatus, the host computer, and the management computer are connected to each other via a network, is provided according to the present invention. The storage apparatus includes a plurality of kinds of storage media with different I/O performance, and a control unit for managing storage areas, which are provided by the plurality of kinds of storage media with the different I/O performance, as a storage tiered; wherein the control unit allocates a storage area from the storage tiered to a data storage area of a volume or volumes storing the data in response to a request from the host computer to write the data, obtains I/O frequency information of the data stored in the volume or volumes, and provides it to the management computer; wherein the management computer includes a storage unit for storing a pool structure information table for managing structure information of the storage tiered and a control unit for managing the structure of the storage tiered of the storage apparatus; and wherein the control unit obtains storage media information, including the I/O frequency of data stored in the volume or volumes, as well as structure information and the I/O performance of the storage media, from the storage apparatus, identifies a storage area of storage media with low I/O performance, which are not allocated to any of the volumes, from among the storage media with higher I/O performance than the I/O frequency of the data stored in the volume or volumes, on the basis of the structure information of the storage media, and issues an instruction to the storage apparatus to create the storage tiered by using a storage area of the identified storage media. 
     If the above-described configuration is used when adding a specified area of storage media to a storage tiered in response to a request from the host computer, the storage media information, including the I/O frequency of the data storage area of the volume(s) as well as the performance information and structure information of the storage media, can be obtained from the storage apparatus; one or more storage media which have not been allocated to the volume(s) with the I/O performance in excess of the I/O frequency can be identified based on the structure information of the storage media so that the data storage area of the volume(s), to which a specified storage area in the storage tiered is allocated, would achieve a specified I/O performance target; an instruction can be issued to the storage apparatus to create a storage tiered by using the identified storage media; and the storage apparatus can create the storage tiered that satisfies the desired performance, in accordance with the instruction. As a result, a low-cost storage tiered can be created by effectively utilizing the storage media in the storage apparatus. 
     Advantageous Effects of Invention 
     According to the present invention, storage media retained by a user can be utilized effectively and a low-cost storage tiered can be configured. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a block diagram showing a hardware configuration of a computer system according to a first embodiment of the present invention. 
         FIG. 2  is a block diagram showing the configuration of a management computer according to the first embodiment. 
         FIG. 3  is a block diagram showing the configuration of a host computer according to the first embodiment. 
         FIG. 4  is a block diagram showing the configuration of a storage apparatus according to the first embodiment. 
         FIG. 5  is a chart showing the content of a storage media information table according to the first embodiment. 
         FIG. 6  is a chart showing the content of an lops information table according to the first embodiment. 
         FIG. 7  is a chart showing the content of a structural ratio information table according to the first embodiment. 
         FIG. 8  is a graph showing IOPS distribution according to the first embodiment. 
         FIG. 9  is a flowchart illustrating a processing sequence for structural ratio calculation processing according to the first embodiment. 
         FIG. 10  is a flowchart illustrating a processing sequence for processing for calculating an allocated capacity of storage media according to the first embodiment. 
         FIG. 11  is a conceptual diagram showing a storage tiered creation instruction screen according to the first embodiment. 
         FIG. 12  is a conceptual diagram showing a display screen that presents the structure of a storage tiered according to the first embodiment. 
         FIG. 13  is a conceptual diagram showing a display screen that prompts a user to purchase storage media according to the first embodiment. 
         FIG. 14  is a conceptual diagram explaining data migration according to the first embodiment. 
         FIG. 15  is a block diagram showing a hardware configuration of a storage apparatus according to a second embodiment of the present invention. 
         FIG. 16  is a flowchart illustrating a processing sequence for structural ratio calculation processing according to the second embodiment. 
         FIG. 17  is a flowchart illustrating a processing sequence for the structural ratio calculation processing according to the second embodiment. 
         FIG. 18  is a conceptual diagram showing a storage tiered switching instruction screen according to the second embodiment. 
         FIG. 19  is a conceptual diagram explaining data migration according to the second embodiment. 
         FIG. 20  is a block diagram showing a hardware configuration of a storage apparatus according to a third embodiment of the present invention. 
         FIG. 21  is a chart showing the content of a storage tiered information table according to the third embodiment. 
         FIG. 22  is a flowchart illustrating a processing sequence for structural ratio calculation processing according to the third embodiment. 
         FIG. 23  is a flowchart illustrating a processing sequence for the structural ratio calculation processing according to the third embodiment. 
         FIG. 24  is a flowchart illustrating a processing sequence for the structural ratio calculation processing according to the third embodiment. 
         FIG. 25  is a conceptual diagram showing an input screen for advance settings according to the third embodiment. 
         FIG. 26  is a conceptual diagram showing a display screen that presents the structure of storage media to be added according to the third embodiment. 
         FIG. 27  is a conceptual diagram explaining a specific example of processing for calculating the structure of additional capacity according to the third embodiment. 
         FIG. 28  is a block diagram of a hardware configuration of a computer system according to a fourth embodiment of the present invention. 
         FIG. 29  is a block diagram showing the configuration of a storage apparatus according to the fourth embodiment. 
         FIG. 30  is a chart showing the content of an external connection volume information table according to the fourth embodiment. 
         FIG. 31  is a chart showing the content of a storage media information table according to the fourth embodiment. 
         FIG. 32  is a flowchart illustrating a processing sequence for structural ratio calculation processing according to the fourth embodiment. 
         FIG. 33  is a flowchart illustrating a processing sequence for structural ratio calculation processing according to the fourth embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     An embodiment of the present invention will be explained in detail with regard to the drawings. In this embodiment, an explanation will be given by taking a storage apparatus as an example of a storage control device. The storage control device can be distinguished by, for example, checking whether it contains physical storage devices or not. An example of a storage control device capable of containing physical storage devices is a storage apparatus. An example of a storage control device which does not contain physical storage devices is a switch device. The switch device can provide a host computer with physical storage devices belonging to an external storage apparatus as if they were storage devices in the switch device. 
     Incidentally, various kinds of information may sometimes be explained by using the expression “xxx table”; however, the various kinds of information may be expressed with a data structure other than a table. The expression “xxx information” can be also used instead of “xxx table” in order to indicate that the various kinds of information do not depend on the data structure. An ID (identifier) or number will be used to identify the relevant element in the following explanation, but other kinds of information (for example, a name) may be used as identification information. 
     A “program” may be used as a subject in the following explanation in order to describe processing; however, since a program is executed by a processor (for example, CPU (Central Processing Unit)) to perform defined processing by using memory resources (for example, a memory) and/or communication interface device (for example, a communication port) as necessary, the subject of the processing may be the processor. Processing described by using a program as a subject may be processing executed by a storage apparatus, a controller for the storage apparatus, or a management computer. The processor may contain a hardware circuit for executing any part of or the entire processing executed by the processor. A computer program may be installed from a program source to each computer. The program source may be, for example, a program distribution server or storage media. 
     (1) First Embodiment 
     (1-1) Outline of this Embodiment 
     The outline of this embodiment will be explained. Recently, an amount of data dealt by a computer system has been increasing explosively. Along with an increase of the data amount, it is necessary to purchase new volumes as needed and add the volumes to a storage apparatus. The storage apparatus manages a plurality of hard disk drives by means of a RAID system. Then, the storage apparatus logicalizes physical storage areas of the plurality of hard disk drives and provides them as logical volumes to a host computer. The host computer accesses the provided logical volumes and requests reading/writing of data. 
     There is a function called Thin Provisioning as one of methods for providing logical volumes to a host computer. The thin provisioning function is a function providing virtualized logical volumes which do not have physical storage areas (hereinafter referred to as virtual volumes), to the host computer, and dynamically allocating the storage areas to the virtual volumes as triggered by write access by the host computer to the virtual volumes. The above-described thin provisioning function has the advantage that the virtual volumes of a larger capacity than that of storage areas, which can be actually provided, can be provided to the host computer and an inexpensive computer system can be configured by reducing the physical storage capacity, which should be prepared in advance, in a storage apparatus. 
     Furthermore, a method for managing each storage area provided by each of a plurality of kinds of storage media with different performance, which are mounted in a storage apparatus, as a plurality of kinds of different storage tiereds is suggested as a data management method for the storage apparatus equipped with the above-described thin provisioning function. Also, a technique called dynamic tiered control to migrate data in a storage tiered according to access frequency from the host computer is suggested. For example, storage areas are allocated from a high-speed and high-performance storage tier to an area where data with high access frequency is stored; and storage areas are allocated from a low-speed and low-performance storage tier to an area of the virtual volumes where data with low access frequency is stored. Furthermore, a technique of sorting data according to performance requirements and allocating storage areas of a high-performance storage tier to an area where data of a high performance requirement is stored is disclosed. 
     If the above-described dynamic tiered control technique is used, cost performance for the storage apparatus can be enhanced. Accordingly, data stored in normal logical volumes are often managed by migrating such data to a storage tiered. Therefore, a sizing tool for calculating the structure of an appropriate storage tiered in accordance with a performance request from a user is provided. This sizing tool estimates IOPS distribution by using a template of an IPO (I/O per Second) pattern of each application retained by the sizing tool in advance on the basis of the capacity of a storage tiered requested by the user and the types of applications used by the user. The IOPS herein used is a value indicative of I/O frequency of data, which is the number of I/O accesses per second to storage media. Furthermore, the IOPS distribution is information indicative of distribution of pages sorted in descending order of IOPS information. Then, an appropriate combination of storage media is selected from a list of combinations of storage media retained by the sizing tool in advance and the structure of a storage tiered that realizes appropriate performance and cost is calculated based on IPOS limit information of each storage media. 
     However, when the structure of the storage tiered is calculated by using a predefined combination of storage media, it sometimes results in a higher-cost structure than a case where storage media actually retained by the user are used. Furthermore, the structure of the storage tiered calculated by using the combination of the predefined storage media may sometimes include storage media, which are not actually retained by the user, or have a capacity shortage even if the storage media are retained by the user, so that the requested storage tiered cannot be created. In this case, it is necessary to purchase new storage media to replenish the storage media which are not retained by the user or to overcome the capacity shortage in order to realize the calculated structure of the storage tiered. So, the problem is that the storage media retained by the user cannot be utilized effectively. 
     So, in this embodiment, IOPS distribution of an existing logical volume and the type and capacity of storage media held by the user are obtained from the storage apparatus; storage media with the lowest performance is selected; the capacity requiring the performance of such storage media is calculated; and the calculated capacity is compared with the capacity of the storage media retained by the user. If the calculated capacity is equal to or less than the capacity of the storage media held by the user, storage media of the calculated capacity is allocated to a storage tiered from the capacity of the storage media held by the user. On the other hand, if the calculated capacity is more than the capacity of the storage media held by the user, the entire capacity of the storage media held by the user is allocated to a storage tiered; and regarding the remaining required capacity, storage media with the next lower performance is selected and the capacity of such storage media is allocated to the storage tiered. As a result, a storage tiered that satisfies the desired performance can be configured by recognizing the type and capacity of the storage media of the storage apparatus held by the user and using such storage media. 
     (1-2) Hardware Configuration of Computer System 
     Next, the hardware configuration of a computer system  100  will be explained. Referring to  FIG. 1 , the computer system  100  is constituted from a management computer  300 , a host computer  500 , and a storage apparatus  600 . 
     Incidentally, for ease of explanation,  FIG. 1  shows the configuration including one host computer  500  and one storage apparatus  600 ; however, the configuration is not limited to the above configuration and a plurality of host computers and a plurality of storage apparatuses may be included. 
     Furthermore, a management interface  670  for the storage apparatus  600 , a management interface  570  for the host computer  500 , and a management interface  499  for the management computer  300  are connected via a specified management network  190 . Consequently, the management computer  300  can communicate with the storage apparatus  600  and the host computer  500 . The management network  190  can be, for example, a LAN (Local Area Network)  190 ; and if the management network  190  is a LAN, the management interfaces  400 ,  570 ,  670  can be, for example, LAN cards. 
     Furthermore, a communication port  680  for the storage apparatus  600  and a data interface  580  for the host computer  500  are connected via a specified data communication network  200 . Consequently, the storage apparatus  600  can communicate with the host computer  500  each other. The data communication network  200  can be, for example, a SAN (Storage Area Network)  200 ; and if the data communication network  200  is a SAN, the data interface  580  can be, for example, an HBA (Host Bus Adapter). 
     The management computer  300  is a computer device for maintaining and managing the storage apparatus  600 . The host computer  500  sends a data read/write request to the storage apparatus  600  connected via the data communication network  200 . Also, the storage apparatus  600  interprets commands sent from the host computer  500  connected via the data communication network  200  and executes data reading from or data writing to storage media in the storage apparatus  600 . 
     A case where a storage tiered is created in the storage apparatus  600  by using the storage media retained in the storage apparatus  600  will be explained below. This embodiment can be used in a case where a new storage tiered is created or a case where an existing logical volume is migrated to a storage tiered. However, when a new storage tiered is created, a logical volume that is a target for obtaining necessary IOPS distribution to calculate the structure of the storage tiered does not exist. Therefore, it is necessary to calculate the structure of the storage tiered by estimating the IOPS distribution based on, for example, the capacity of the storage tiered requested by the user and IOPS pattern information defined in advance. 
     (1-2-1) Configuration of Management Computer 
     Next, the configuration of the management computer  300  will be explained. Referring to  FIG. 2 , the management computer  300  is constituted from, for example, an input device  310 , an output device  320 , a processor (indicated as CPU in the drawing)  330 , a disk device  340 , a memory  350 , and a management interface  400 . The management computer  300  is composed of, for example, a personal computer or a workstation. 
     The input device  310  is a device used by a user such as a system administrator to issue instructions to the management computer  300 . Examples of the input device  310  can include a keyboard, a pointing device, a switch, a touch panel, and a microphone. The output device  320  is a device used by the management computer  300  to output information to the user such as the system administrator. Examples of the output device  320  can include a monitor display, a speaker, and a printer. 
     The processor  330  realizes various functions described later by controlling the operation of the management computer  300  in accordance with, for example, programs and operation parameters stored in the memory  350 . The disk device  340  is a physical storage device and examples of the disk device  340  can include HDD and SSD (Solid State Drive). Regarding the HDD, there are HDD in accordance with SAS (hereinafter referred to as SAS) and HDD in accordance with SATA (hereinafter referred to as SATA). 
     The memory  350  stores, for example, a structural ratio calculation program  360 , a storage media information table  370 , an IOPS information table  380 , and a structural ratio information table  390 . The details of the storage media information table  370 , the IOPS information table  380 , and the structural ratio information table  390  will be explained later. 
     The structural ratio calculation program  360  is a computer program for calculating the structure of the storage media based on the IOPS distribution in response to a request entered by the user such as the system administrator to the input device  310 . Specifically speaking, the structural ratio calculation program  360  identifies the structure of the storage media allocated to a designated logical volume, compares the identified storage media with information of the storage media actually retained by the user, creates a storage tiered having the calculated structure, and issues an instruction to the device management program  630 , the storage media management program  640 , and the dynamic tiered tontrol program  660  for the storage apparatus  600  to execute processing such as migration of existing data. Processing of the structural ratio calculation program  360  will be explained later in detail. 
     The management interface  400  is a communication interface used by the management computer  300  to access the storage apparatus  600  via the management network  190 . 
     Incidentally, when the CPU executes processing based on the structural ratio calculation program  360 , an explanation will be given by referring to the structural ratio calculation program  360  as a subject. 
     (1-2-2) Configuration of Host Computer 
     Next, the configuration of the host computer  500  will be explained. Referring to  FIG. 3 , the host computer  500  is constituted from, for example, an input device  510 , an output device  520 , a processor (indicated as CPU in the drawing)  530 , a disk device  540 , a memory  550 , a management interface  570 , and a data interface  580 . The host computer  500  is a computer device issuing I/O commands. 
     The input device  510  is a device used by the user to issue I/O commands via the host computer  500  to the storage apparatus  500  connected via the host computer  300  and the data interface  580 . Examples of the input device  510  can include a keyboard, a pointing device, a switch, a touch panel, and a microphone. The output device  520  is a device used by the management computer  300  to output information to the user. Examples of the output device  520  can include a monitor display, a speaker, and a printer. 
     The processor  530  controls the operation of the host computer  500  in accordance with, for example, programs and operation parameters stored in the memory  550 . The disk device  540  is a physical storage device and examples of the disk device  540  can include HDD and SSD. Regarding the HDD, there are HDD in accordance with SAS (hereinafter referred to as SAS) and HDD in accordance with SATA (hereinafter referred to as SATA). 
     The memory  550  stores, for example, an application  560 . The memory  550  may store a plurality of applications. 
     The management interface  570  is a communication interface for accessing the management computer  300  via the management network  190 . The data interface  580  is a communication interface for accessing the storage apparatus  600  via the data communication network  200 . 
     (1-2-3) Configuration of Storage Apparatus 
     Next, the configuration of the storage apparatus  600  will be explained. Referring to  FIG. 4 , the storage apparatus  600  is constituted from, for example, a disk controller  605 , an existing volume  700  and volumes  710 . 
     The disk controller  605  includes a processor (indicated as CPU in the drawing)  610 , a memory  620 , a management I/F  670 , communication ports  680 , and a disk interface  690 . 
     The processor  610  realizes various functions described later by controlling the operation of the storage apparatus  600  in accordance with, for example, programs and operation parameters stored in the memory  620 . The memory  620  stores, for example, a device management program  630 , a storage media management program  640 , an IOPS counter  650 , and a dynamic tiered tontrol program  660 . 
     This embodiment can be used in a case where a new storage tiered is created or a case where an existing logical volume  700  is migrated to a storage tiered. However, when a new storage tiered is created, a logical volume that is a target for obtaining necessary IOPS distribution to calculate the structure of the storage tiered does not exist. Therefore, the IOPS distribution is estimated based on, for example, the capacity of the storage tiered requested by the user and IOPS pattern information defined in advance. When estimating the IOPS distribution from the predefined information, it is unnecessary to provide the IOPS counter  650  in the memory  620  to store an I/O counter. 
     The device management program  630  is a computer program for managing the storage apparatus  600 . The device management program  630  accepts I/O from, for example, the host computer  500 , sets various settings to the storage apparatus  600 , and collects information from the storage apparatus  600 . 
     The storage media management program  640  is a computer program for managing logical volumes in the storage apparatus  600 . The storage media management program  640 , for example, creates or deletes the volumes  710  in the storage apparatus  600  and collects various information about the volumes. 
     The IOPS counter  650  is a computer program for managing the number of times of accesses to the existing volume  700  in the storage apparatus  600 . The IOPS counter  650 , for example, calculates an average of the number of times of accesses per second (IOPS) to the existing volume  700  in the storage apparatus  600 . Furthermore, the IOPS counter  650  increases or decreases the number of times of accesses to the existing volume  700  in the storage apparatus  600 . 
     The dynamic tiered tontrol program  660  is a computer program for managing the operation of the storage tiered. The dynamic tiered tontrol program  660 , for example, creates or deletes a storage tiered in the storage apparatus  600 . Furthermore, the dynamic tiered tontrol program  660  obtains the IOPS from the IOPS counter  650  and creates IOPS distribution by sorting the IOPS in descending order of the number of IOPS. The IOPS distribution will be explained later in detail. 
     The management interface  670  is a communication interface for accessing the management computer  300  and the host computer via the management network  190 . The communication port  680  is a communication interface for accepting access from the host computer  500  via the data communication network  200 . 
     The disk interface  690  is an interface used by the disk controller  605  to access the existing volume  700  or the volume  710 . The existing volume  700  is a volume, such as a physical volume or a logical volume or a pool, in which data is already stored. Examples of the physical volume can include various devices capable of reading/writing data, such as hard disk drives, semiconductor memory devices, optical disk devices, and magneto-optical disk devices. 
     If the hard disk devices are to be used, for example, FC (Fibre Channel) disks, SCSI (Small Computer System Interface) disks, SATA disks, ATA (Attachment) disks, and SAS (Serial Attached SCSI) disks can be used. Also, storage devices such as flash memory, FeRAM (Ferroelectric Random Access Memory), MRAM (Magnetoresistive Random Access Memory), phase change memory (Ovonic Unified Memory), and RRAM (Resistance RAM) may be used. 
     The volume  710  is a physical volume or a logical volume and is a volume that can be used for a storage tiered. Examples of the physical volume can be the same storage devices of the existing volume  700 . 
     (1-3) Structural Ratio Calculation Processing 
     Next, structural ratio calculation processing executed by the structural ratio calculation program  360  of the management computer  300  will be explained. Before explaining the details of the structural ratio calculation processing, various kinds of information stored in the memory  350  for the management computer  300  will be explained. 
     The storage media information table  370  is a table for managing various kinds of information of each storage media in the storage apparatus  600  and is constituted from a tier order column  3701 , a storage media type column  3702 , a capacity column  3703 , an IOPS limit column  3704 , and a use authority column  3705  as shown in  FIG. 5 . The tier order column  3701  stores information indicating the tier order of the storage media. Specifically speaking, the tier order according to the size of an IOPS limit for the storage media is stored. The storage media type column  3702  stores information indicating the type of the storage media and stores, for example, “SSD” or “SAS15K.” The capacity column  3703  stores information indicating the capacity of each storage media. The IOPS limit column  3704  stores information indicating the IOPS limit for each storage media. The IOPS limit is the maximum number of IOPS for each page that can be processed by each storage media. The information stored in the IOPS limit column  3704  may be a predefined value or a value counted by the IOPS counter  650  after actual transmission of test I/O by the device management program  630  of the storage apparatus  600  to the volume  710 . The use authority column  3705  stores information indicating the use authority of each user with respect to each storage media. 
     In the environment where the use authority is set to each storage media, for example, user A can select storage media to use only from an aggregate of storage media over which the user authority is granted to user A. For example, user A can select and use, for example, SSD with a capacity of 20 GB in the tier order 1 and SAS15 with a capacity of 30 GB in the tier order 2. However, user A cannot select storage media over which the use authority is granted to only user B (SAS15K with a capacity 20 of GB in the tier order 2 and SATA50GB in the tier order a) or storage media over which the use authority is not granted to any user at present (SAS15K with a capacity of 10 GB in the tier order 2). 
     The IOPS information table  380  is a table for managing the number of IOPS for each page of the existing volume  700  and is constituted from a page ID column  3801 , a number-of-TOPS column  3802 , and an allocation state column  3803  as shown in  FIG. 6 . The page ID column  3801  stores information for identifying a page of the existing volume  700 . The number-of-TOPS column  3802  stores the number of IOPS of data stored in each page. The allocation state column  3803  stores information indicating an allocation state of the storage media to each page. For example, if the storage media to be allocated to each page is calculated by the structural ratio calculation program  360 , OK is stored; and if the storage media to be allocated to each page is not calculated by the structural ratio calculation program  360 , the relevant field remains as a blank space. 
     The structural ratio information table  390  is a table for managing the structure of a storage tiered and is constituted from a tier column  3901 , a storage media type column  3902 , and a capacity column  3903  as shown in  FIG. 7 . The tier column  3901  stores information for identifying each tier of the storage tiered. The storage media type column  3902  stores information indicating the type of storage media constituting each tier. The capacity column  3903  stores information indicating the capacity of storage media to be allocated to each tier. Under this circumstance, the capacity of the storage media is calculated from a capacity area defined for an area corresponding to a page(s) storing data and the number of areas corresponding to a page(s) to which such storage media is to be allocated. Also, the capacity of the storage media may include a control area of the data besides a storage area of the data.  FIG. 7  shows that Tier 1 is composed of SSD storage media and the capacity of Tier 1 is 10 GB; and Tier 2 is composed of SAS15K storage media and the capacity of Tier 2 is 20 GB. 
     Next, the IOPS distribution will be explained.  FIG. 8  is a graph indicating IOPS distribution  1100  and the IOPS distribution is obtained by sorting pages in descending order of IOPS of data stored in each page on the basis of the information stored in the IOPS information table  380  and the storage media information table  370 . As shown in  FIG. 8 , the vertical axis  1110  of the IOPS distribution  1100  represents the number of I/O per second and the horizontal axis  1120  represents the page ID and each bar  1130  represents IOPS from the host computer  500  to data stored in the corresponding page ID. 
     As shown in  FIG. 8 , for example, an IOPS limit ( 1500 ) in a case where the storage media type is SATA is obtained from the storage media information table  370 ; a value of that IOPS limit is plotted on the vertical axis  1110 ; and a dashed line  1140  is drawn in the IOPS distribution  1100 . The dashed line  1140  makes it possible to realize the capacity of pages with the IOPS which requires the storage media having performance of SATA or higher performance and for which performance of SATA is sufficient. Furthermore, an IOPS limit ( 3500 ) in a case where the storage media type is SAS is obtained from the storage media information table  370 ; a value of that IOPS limit is plotted on the vertical axis  1110 ; and a dashed line  1150  is drawn in the IOPS distribution  1100 . The dashed line  1150  makes it possible to realize the capacity of pages with the IOPS which requires the storage media having performance of SAS or higher performance and for which performance of SAS is sufficient. Furthermore, an IOPS limit ( 5000 ) in a case where the storage media type is SSD is obtained from the storage media information table  370 ; a value of that IOPS limit is plotted on the vertical axis  1110 ; and a dashed line  1160  is drawn in the IOPS distribution  1100 . The dashed line  1160  makes it possible to realize the capacity of pages with the IOPS which requires the storage media having performance of SSD or higher performance and for which performance of SSD is sufficient. Therefore, the use of the IOPS distribution  1100  makes it possible to calculate the capacity of the IOPS, for which the performance of each storage media is sufficient, and identify an ideal structure of storage media corresponding to the IOPS distribution. 
     Next, the details of the structural ratio calculation processing executed by the structural ratio calculation program  360  will be explained. When a request for creation of a storage tiered is made in response to input by the user,  FIG. 9  shows a processing sequence executed by the structural ratio calculation program  360  for calculating the structure of the storage tiered with respect to the requested IOPS distribution. 
     The structural ratio calculation processing described below is executed when an instruction to create a storage tiered is issued by means of input by the user. The storage tiered creation instruction is issued via a storage tiered creation instruction screen  1200 . Now, the details of the storage tiered creation instruction screen  1200  will be explained. Referring to  FIG. 11 , the storage tiered creation instruction screen  1200  includes a radio button  1210  for selecting a method for obtaining the performance of the storage tiered to be created, a selection box  1220  for selecting an existing volume, an OK button  1230  for commanding the execution of the processing, and a cancel button  1240  for terminating the screen without executing the processing. 
     The radio button  1210  is mainly used when a storage tiered is created based on the IOPS distribution obtained from data of the existing volume  700 . If data which should be the basis of the IOPS distribution does not exist and a storage tiered is newly created, the IOPS distribution is estimated based on the performance of the application(s)  560  in the memory  550  for the host computer  500 . In this case, a text box for inputting the capacity of the storage tiered, a selection box for selecting a performance pattern of the application, and an add button for increasing input items when there are a plurality of applications may be included as necessary items for estimating the IOPS distribution. Furthermore, a screen by which the user directly creates the IOPS distribution may be displayed. 
     Referring back to  FIG. 9 , the structural ratio calculation program  360  firstly obtains the IOPS distribution  1100  of the existing volume  700  from the storage apparatus  600  (S 100 ). Specifically speaking, the structural ratio calculation program  360  issues an instruction to the dynamic tiered tontrol program  660  of the storage apparatus  600  to obtain the IOPS information of the existing volume  700  and create the IOPS distribution  1100  shown in  FIG. 8 . However, if a storage tiered is to be newly created, the logical volume  710  which is a target to obtain necessary IOPS distribution for calculating the structure of the storage tiered does not exists, so that the IOPS distribution is estimated based on, for example, the capacity of the storage tiered requested by the user and the predefined IOPS pattern information. 
     Subsequently, the structural ratio calculation program  360  refers to the storage media information table  370  and obtains information of the storage media in the storage apparatus  600  (S 110 ). 
     Then, the structural ratio calculation program  360  judges whether or not the user authority is set to the storage media obtained in step S 110  (S 120 ). If it is determined in step S 120  that the user authority is set to the storage media, the structural ratio calculation program  360  obtains only information of the storage media to which the user authority is set (S 130 ). Specifically speaking, the structural ratio calculation program  360  refers to the use authority column  3705  of the storage media, which is a target of the storage media information table  370 , and obtains only the storage media which can be used by the user as a storage tiered. On the other hand, if it is determined in step S 120  that the user authority is not set to the storage media, the structural ratio calculation program  360  executes processing in step S 140 . 
     Next, the structural ratio calculation program  360  identifies the IOPS in excess of the IOPS limit for the existing volume  700  in the storage apparatus  600  and increases the number of IOPS (S 140 ). Specifically speaking, the structural ratio calculation program  360  refers to the IOPS distribution of the existing volume  700  obtained in step S 100  and identifies the IOPS in excess of the IOPS limit. The IOPS in excess of the IOPS limit herein used means, for example, the IOPS in excess of the dashed line  1140 ,  1150 ,  1160  of the IOPS limit for each storage media or the IOPS in the vicinity of the dashed lines  1140  and so on as shown in  FIG. 8 . Then, the structural ratio calculation program  360  issues an instruction to the dynamic tiered tontrol program  660  of the storage apparatus  600  to increase the number of IOPS of the identified IOPS. 
     Next, the structural ratio calculation program  360  obtains the storage media with the lowest IOPS limit from among the information of the storage media obtained in step S 110  (S 150 ). This means that, on the basis that the performance of the storage media is proportional to the cost of the storage media, a storage tiered is created with the lowest-cost storage media from among the storage media in the storage apparatus  600  by selecting the storage media with the lowest IOPS limit. However, if the performance of the storage media is not proportional to the cost of the storage media, the storage media may be selected in accordance with characteristics of the storage media which satisfy the cost of the storage media and other requirements. 
     Next, the structural ratio calculation program  360  calculates the allocated capacity of the storage media selected in step S 150  (S 160 ). Processing for calculating the allocated capacity of the storage media in step S 160  will be explained later in detail. 
     Subsequently, the structural ratio calculation program  360  creates the storage tiered based on the calculation result in step S 160  (S 170 ). Specifically speaking, the structural ratio calculation program  360  refers to the structural ratio information table  390 , in which the calculation result in step S 160  is reflected, and issues an instruction to the device management program  630  of the storage apparatus  600  to create the storage tiered in accordance with structural ratio information of the structural ratio information table  390 . 
     The structural ratio calculation program  360  may present the structure of the storage tiered to the user before issuing the instruction to the device management program  630  of the storage apparatus  600  to create the storage tiered. For example, the structural ratio calculation program  360  displays a display screen  1300  shown in  FIG. 12  and presents the structure of the storage tiered to the user. The display screen  1300  includes a structure list  1310  of the storage tiered to be created, an OK button  1320  for executing the storage tiered creation instruction, and a cancel button  1330  for terminating the screen without executing the storage tiered creation instruction. 
     The content to be displayed on the display screen  1300  may be designed so that the structure of the storage tiered is presented based on the structural ratio information table  390  by, for example, integrating several tiers in accordance with a constraint(s) of the dynamic tiered control. 
     Referring back to  FIG. 9 , the structural ratio calculation program  360  copies data to the storage tiered created in step S 170  in descending order of the IOPS of the data, starting from the highest IOPS (S 180 ). Specifically speaking, the structural ratio calculation program  360  refers to the IOPS distribution obtained in step S 100  and issues an instruction to the device management program  630  of the storage apparatus  600  to migrate the data to the created storage tiered in descending order of the IOPS of the data, starting from the highest IOPS. 
     Next, the details of the processing for calculating the allocated capacity of the storage media in step S 160  will be explained. As shown in  FIG. 10 , the structural ratio calculation program  360  obtains the IOPS limit for the storage media selected in step S 150  (S 210 ). 
     Next, the structural ratio calculation program  360  calculates the capacity of pages for which the performance of the selected storage media sufficiently satisfies the IOPS (hereinafter referred to as the ideal capacity), on the basis of the information of the IOPS distribution obtained in step S 100  and the IOPS limit for the storage media obtained in step S 210  (S 220 ). For example, assuming that the structural ratio calculation program  360  selects SATA in step S 150 , it identifies the capacity of pages (the number of pages) which requires the storage media with the performance of SATA and higher performance and for which the performance of SATA is sufficient, on the basis of the IOPS distribution shown in  FIG. 8  and the IOPS limit for SATA as shown with the dashed line  1140 . 
     Next, the structural ratio calculation program  360  obtains the capacity of the storage media selected in step S 150  (hereinafter referred to as the retained capacity) from among the information of the storage media retained in the storage apparatus  600  obtained in step S 110  (S 230 ). 
     Then, the structural ratio calculation program  360  compares the ideal capacity calculated in step S 220  with the retained capacity obtained in step S 230  (S 240 ). 
     If it is determined in step S 240  that the ideal capacity is larger than the retained capacity, the structural ratio calculation program  360  sets the retained capacity as the allocated capacity of the selected storage media (S 250 ). The case where the ideal capacity is larger than the retained capacity means that the capacity of the target storage media in the storage apparatus  600  is less than the ideal capacity of the storage media derived from the IOPS distribution calculated in step S 220 . 
     If it is determined in step S 240  that the retained capacity is equal to or more than the ideal capacity, the structural ratio calculation program  360  sets the ideal capacity as the allocated capacity of the selected storage media (S 260 ). The case where the retained capacity is equal to or more than the ideal capacity means that the capacity of the target storage media in the storage apparatus  600  exceeds the ideal capacity of the storage media derived from the IOPS distribution calculated in step S 220 . 
     Next, the structural ratio calculation program  360  associates the allocated capacity of the storage media calculated in step S 250  or  260  with the selected storage media and stores them in the structural ratio information table  390  (S 270 ). 
     Then, the structural ratio calculation program  360  stores “OK,” which indicates that the storage media is allocated to the relevant page, in the allocation state column  3803  of the IOPS information table  380  with respect to the page to which the selected storage media is allocated (S 280 ). 
     Subsequently, the structural ratio calculation program  360  compares the capacity of the storage media written to the structural ratio information table  390 , that is, a total of the allocated capacity (hereinafter referred to as the total allocated capacity) with the desired capacity of the storage tiered (S 290 ). 
     If it is determined in step S 290  that the total allocated capacity is equal to or more than the desired capacity of the storage tiered, the structural ratio calculation program  360  terminates the allocated capacity calculation processing. 
     If it is determined in step S 290  that the total allocated capacity is less than the desired capacity of the storage tiered, the structural ratio calculation program  360  executes processing in step S 300 . 
     Subsequently, the structural ratio calculation program  360  judges whether the storage media with the next lower IOPS limit exists or not (S 300 ). If it is determined in step S 300  that the storage media with the next lower IOPS limit exists, the structural ratio calculation program  360  selects such storage media (S 320 ) and repeats the processing in step S 210  and subsequent steps. On the other hand, if it is determined in step S 300  that the storage media with the next lower IOPS limit does not exist, the structural ratio calculation program  360  presents a screen for prompting the user to purchase necessary storage media to the user (S 310 ). Specifically speaking, if there is no storage media with the next lower IOPS limit next, the structural ratio calculation program  360  identifies the type and capacity of necessary storage media to calculate the ideal structure, which satisfies the IOPS distribution, and presents the screen for prompting the user to purchase such storage media to the user. 
     A method for identifying the necessary storage media in step  310  is to, for example, select the storage media with the lowest IOPS limit and calculate the ideal capacity, which sufficiently satisfies the IOPS, of the storage media selected based on the IOPS limit for such storage media. Next, the retained capacity of the selected storage media in the storage apparatus  600  is obtained and the retained capacity is subtracted from the ideal capacity, thereby calculating necessary capacity to be added. This calculation is repeated for all the types of storage media and the additional capacity of all the storage media is calculated. Then, the structural ratio calculation program  360  displays the additional capacity of all the storage media as a list of necessary storage media to be purchased on a display screen  1400  shown in  FIG. 13 . 
     The display screen  1400  shown in  FIG. 13  is a screen for prompting the user to purchase necessary storage media and displays a sentence stating “Please purchase the following storage media” together with the type and capacity of the necessary storage media to be purchased.  FIG. 13  shows that 5 GB of storage media whose type is SSD needs to be purchased. 
     Referring back to  FIG. 10 , after showing the screen for prompting the user to purchase the necessary storage media in step S 310 , the structural ratio calculation program  360  clears the content stored in the structural ratio information table  390  and terminates the processing because it cannot create the storage tiered which satisfies the IOPS distribution. 
     Next, migration from the existing volume  700  to the storage tiered will be explained.  FIG. 14  shows that data of an existing volume  1520  is migrated to a storage tiered  1510  created by the above-described structural ratio calculation processing. The storage tiered  1510  is composed of storage media such as SSD  1530 , SAS  1540 , and SATA  1550 . Data stored in the existing volume  1520  is indicated in IOPS distribution  1560  where the data is sorted in descending order of the IOPS. In this embodiment, data stored in the existing volume  1520  is migrated sequentially in descending order of the IOPS to the created storage tiered  1510 . The data is sequentially written to the storage tiered  1510 , starting from the SSD  1530  with the highest performance, by means of the storage tiered control function; and when the capacity of the SSD  1530  becomes filled with the data, the data is then written to the storage media of the SAS  1540  with the next higher performance. Furthermore, when the capacity of the SAS  1540  becomes filled with the data, the data is then written to the SATA  1550  with the next higher performance. 
     (1-4) Advantageous Effect of this Embodiment 
     According to this embodiment as described above, when adding a specified area of storage media to the existing volume  700  in response to a request from the host computer  500 , the management computer  300 : obtains the storage media information, including the I/O frequency of the data storage area (page) of the existing volume  700  as well as the performance information and structure information of the storage media, from the storage apparatus  600 ; identifies one or more storage media which have not been allocated to the existing volume  700  with the I/O performance in excess of the I/O frequency so that the data storage area of the existing volume  700  would achieve a specified I/O performance target; and issues an instruction to the storage apparatus to create a storage tiered by using the identified storage media. As a result, a storage tiered that satisfies the desired performance can be configured by recognizing the type and capacity of the storage media of the storage apparatus  600  held by the user and using such storage media. 
     (2) Second Embodiment 
     (2-1) Hardware Configuration of Computer System 
     Since the configuration of a computer system according to this embodiment is almost the same as that in the first embodiment, its detailed explanation has been omitted. Particularly, any difference in the configuration of this embodiment from that of the first embodiment will be explained below in detail. This embodiment describes a case where when switching from an existing virtual volume pool to a storage tiered, the structure of storage media to be added to the storage tiered is calculated. Since the configuration of the management computer  300  and the host computer  500  is almost the same as that in the first embodiment, its detailed explanation has been omitted. 
     (2-1-1) Configuration of Storage Apparatus 
     The difference between a storage apparatus  1600  according to this embodiment and the first embodiment is that the storage apparatus  1600  is equipped with a virtual volume pool  1700  as shown in  FIG. 15 . The thin provisioning function presents a virtual volume to the host computer  500  as described earlier; and if the host computer  500  makes write access to the virtual volume, a storage area is dynamically allocated to the virtual volume. The virtual volume pool  1700  is a storage area allocated to this virtual volume and is a pool for a virtual volume(s). Data has already been written to the virtual volume pool  1700 . Furthermore, the virtual volume pool  1700  is connected to a disk interface  1690 . Since the configuration other than the virtual volume pool  1700  is the same as that of the first embodiment, its detailed explanation has been omitted. 
     (2-2) Structural Ratio Calculation Processing 
     Next, processing for calculating the structure of storage media to be added to the storage tiered when switching from the existing virtual volume pool  1700  to a new storage tiered will be explained. The storage media structure calculation processing is executed by the structural ratio calculation program  360  of the management computer  300 . In the following explanation, the same step number is assigned to the processing of the same content as that of the structural ratio calculation processing according to the first embodiment and its detailed explanation has been omitted. 
     The structural ratio calculation processing according to this embodiment is executed by, for example, issuance of an instruction by the administrator to the structural ratio calculation program  360  of the management computer  300  to create a storage tiered based on the IOPS distribution of the virtual volume pool  1700 . 
     For example, the storage tiered switching instruction is issued via a storage tiered switching instruction screen  1800 . Now, the details of the storage tiered switching instruction screen  1800  will be explained. As shown in  FIG. 18 , the storage tiered switching instruction screen  1800  includes a radio button  1820  for selecting GROWING and a radio button  1830  for selecting GROWTH COMPLETED, which are radio buttons for selecting a capacity growth state of the virtual volume pool to be switched to the storage tiered, a selection box  1840  for selecting the virtual volume pool to be switched to the storage tiered, an OK button  1850  for commanding the execution of the processing, and a cancel button  1860  for terminating the screen without executing the processing. 
     The user checks if the capacity of the target virtual volume pool  1700  to be switched to the storage tiered is growing or not. If the capacity is growing, the user selects the radio button  1820  indicating that the capacity is growing; and if the growth is completed, the user selects the radio button  1830  indicating the growth completion. Furthermore, the user selects the target virtual volume pool to be switched to the storage tiered from the selection box  1840 . The storage tiered switching instruction screen  1800  is designed so that the virtual volume pool is selected from the selection box  1840 ; however, identification information indicating the virtual volume pool  1700  may be directly entered. 
     As shown in  FIG. 16 , the structural ratio calculation program  360  obtains the IOPS distribution of the virtual volume pool  1700  from the storage apparatus  1600  (S 400 ). Specifically speaking, the structural ratio calculation program  360  issues an instruction to the dynamic tiered tontrol program  660  of the storage apparatus  600  to obtain the IOPS information of the virtual volume pool  1700  and create the IOPS distribution. 
     Next, the structural ratio calculation program  360  obtains the information of the capacity growth state of the virtual volume pool  1700  from the host computer  500  (S 410 ). The information about the capacity growth state is information to be obtained in order to judge whether the structure of an appropriate storage tiered should be created in accordance with the capacity growth state of the virtual volume pool  1700  at the time of switching to the storage tiered, or the structure of an appropriate storage tiered should be configured in accordance with the operation status such as extension or deletion of the pool. 
     Next, the structural ratio calculation program  360  judges the growth state of the virtual volume pool  1700  as obtained in step S 410  (S 420 ). If it is determined in step S 420  that the capacity of the virtual volume pool  1700  is growing, the structural ratio calculation program  360  obtains only information of the storage media with the IOPS equal to or more than the IOPS limit for the storage media of the virtual volume pool  1700  (S 430 ). On the other hand, If it is determined in step S 420  that the capacity of the virtual volume pool  1700  is not growing, that is, the growth is completed, the structural ratio calculation program  360  obtains information of all the storage media in the storage apparatus  1600  (S 440 ). 
     Next, the structural ratio calculation program  360  issues an instruction to the dynamic tiered tontrol program  1660  of the storage apparatus  1600  to identify the IOPS in excess of the IOPS limit for the storage media of the virtual volume pool  1700  in the IOPS distribution obtained in step S 400  and increase the number of IOPS (S 450 ). 
     Then, the structural ratio calculation program  360  obtains the storage media with the lowest IOPS limit from among the information of the storage media obtained in step S 110  (S 150 ) and calculates the allocated capacity of the storage media selected in step S 150  (S 160 ). 
     Subsequently, as shown in  FIG. 17 , the structural ratio calculation program  360  gives an instruction to the device management program  1630  of the storage apparatus  1600  to refer to the structural ratio information table  390  and add storage media other than the storage media of the virtual volume pool  1700  to the virtual volume pool  1700 , thereby creating the storage tiered (S 500 ). 
     Next, the structural ratio calculation program  360  judges the growth state of the virtual volume pool  1700  obtained in step S 410  again (S 510 ). 
     If the growth state of the virtual volume pool  1700  indicates the growth completion in step S 510 , the structural ratio calculation program  360  sorts data according to the performance requirement and migrates the data by using the dynamic storage tiered control function that allocates pages of a high performance tier from data of high performance requirement (S 520 ). 
     On the other hand, if the growth state of the virtual volume pool  1700  indicates in step S 510  that the capacity is growing, the structural ratio calculation program  360  migrates data of the allocated capacity of the storage media with a higher IOPS limit than that of the storage media of the virtual volume pool  1700  to the highest-level tier in descending order of the IOPS of the data (S 530 ). 
     After the completion of step S 530 , the structural ratio calculation program  360  identifies data, to which the storage media with a lower IOPS limit than that of the storage media of the virtual volume pool  1700  is allocated, and designates migration destination storage media for such data, thereby migrating the data (S 540 ). 
     Next, in order to delete a storage area equivalent to the capacity of the added storage media, other than the storage media of the virtual volume pool  1700 , from the virtual volume pool  1700 , the structural ratio calculation program  360  migrates data stored in the storage media of the virtual volume pool  1700  to other volumes in the same storage media and deletes the emptied volume(s) (S 550 ). This is normally the processing executed when the growth state indicates the growth completion. However, even if the growth state indicates that the capacity is growing, the screen for checking whether the relevant volume(s) should be deleted or not may be presented to the user and then the volume(s) may be deleted. 
     Next, migration executed when switching from the virtual volume pool  1700  to the storage tiered will be explained.  FIG. 19  shows that data of a virtual volume pool  1910  is migrated to a storage tiered  1920  created by the above-described structural ratio calculation processing. Furthermore,  FIG. 19  shows that the capacity growth of the virtual volume pool  1910  is completed and, for example, the storage tiered  1920  constituted from SSD, SAS and SATA is created by adding SSD and SATA to the virtual volume pool  1910  which is SAS. Then, the data of the virtual volume pool  1910  is migrated to the SSD and SATA of the created storage tiered  1920 . 
     The data of the virtual volume pool  1910  is sorted in descending order of the IOPS of the data as described above, which results in IOPS distribution  1940 . Then, the data equivalent to the allocated capacity of the SSD which is the storage media with a higher IOPS limit than that of the SAS, that is, the storage media of the virtual volume pool  1910 , is migrated. After the data migration to the SSD is completed, data to which the SATA (which is the storage media with a lower IOPS limit than that of the SAS, that is, the storage media of the virtual volume pool  1910 ) is allocated is identified, the storage media which is a data migration destination is designated for such data, and then the data is migrated to the SATA. Furthermore, after the completion of the migration to the SATA, the data stored in the SAS is migrated to other volumes in the same SAS in order to delete the capacity of the added SSD and SATA which are the storage media other than the SAS, that is, the storage media of the virtual volume pool  1910 . Then, a storage tiered  1930  from which the emptied volume(s) has been deleted is created and switching from the virtual volume pool  1910  to the storage tiered  1930  is completed. 
     (2-3) Advantageous Effect of this Embodiment 
     In this embodiment as described above, when a request is made by the host computer  500  to switch from a virtual volume pool to a storage tiered, data can be migrated to that storage tiered by creating a low-cost storage tiered using the storage media retained by the user on the basis of the IOPS distribution of the virtual volume pool. 
     (3) Third Embodiment 
     (3-1) Hardware Configuration of Computer System 
     Since the configuration of a computer system according to this embodiment is almost the same as that in the first and second embodiments, its detailed explanation has been omitted. Particularly, any difference in the configuration of this embodiment from that of the first and second embodiments will be explained below in detail. This embodiment describes a case where as triggered by the receipt of notice of the capacity depletion of a storage tiered, the management computer  300  obtains the capacity to be added to the storage tiered and calculates the structure of storage media with respect to the additional capacity. Since the configuration of the management computer  300  and the host computer  500  are almost the same as that in the first and second embodiments, its detailed explanation has been omitted. 
     The difference between a storage apparatus  2000  according to this embodiment and the first embodiment is that the storage apparatus  2000  is already equipped with a storage tiered  2100  as shown in  FIG. 20 . Data has already written to the storage tiered  2100 . The storage tiered  2100  is also connected to a disk interface  2000 . In a case of the capacity depletion of the storage tiered  2100 , the storage apparatus  2000  notifies the management computer  300  of the depletion. Since the configuration other than the storage tiered  2100  is the same as that of the first embodiment, its detailed explanation has been omitted. 
     The management computer  300  obtains the capacity of the storage media of the storage tiered  2100  obtained by a dynamic tiered tontrol program  2060  of the storage apparatus  2000 . The capacity of the storage media of the storage tiered  2100  is stored in storage tiered information  2200 . The storage tiered information table  2200  may be created by the management computer  300  based on information sent from the storage apparatus  2000  or the storage apparatus  2000  may create the storage tiered  2100  based on information of the capacity of the storage media and information of the storage tiered  2100  may be sent to the management computer  300 . 
     The storage tiered information table  2200  is a table for managing the capacity of storage media of the storage tiered  2200  and is constituted from a tier column  2210 , a storage media type column  2220 , and a capacity column  2230  as shown in  FIG. 21 . The tier column  2210  stores information for identifying each tier. The storage media type column  2220  stores information of the type of storage media corresponding to each tier. Each tier capacity column  2230  stores information of the capacity of the storage media corresponding to each tier. Furthermore, a total capacity field  2240  stores the capacity of the entire storage tiered  2100 . 
     (3-2) Structural Ratio Calculation Processing 
     Next, processing for calculating the structure of storage media of the capacity to be added to the existing storage tiered  2200  will be explained. The storage media structure calculation processing is executed by the structural ratio calculation program  360  of the management computer  300 . In the following explanation, the same step number is assigned to the processing of the same content as that of the structural ratio calculation processing according to the first embodiment and its detailed explanation has been omitted. 
     The structural ratio calculation processing according to this embodiment is executed by, for example, the dynamic tiered tontrol program  2060  of the storage apparatus  2000  as triggered by detection of depletion of the capacity of the storage tiered  2100  during monitoring such capacity and transmission of the detected content to the management computer  300 . 
     Firstly, the structural ratio calculation program  360  receives the notice from the dynamic tiered tontrol program  2060  of the storage apparatus  2000 , reporting that the capacity of the storage tiered  2100  has exceeded a specified capacity threshold, which results in the capacity depletion (S 560 ). Then, the structural ratio calculation program  360  obtains the additional capacity of the entire storage tiered from the storage tiered information table  2200  (S 565 ). 
     The specified capacity threshold in step S 560  or the additional capacity to be added to the storage tiered  2100  may be set in advance by input by the user. For example, the structural ratio calculation program  360  presents an input screen for the advance setting of the extension of the storage tiered  2100  to the user. The user can set the advance setting of the extension of the storage tiered  2100  via, for example, an input screen  2300  shown in  FIG. 25 . The input screen  2300  is used to directly enter a threshold for the capacity of the storage tiered  2100  or set the threshold for the capacity by means of another function, so that whether the capacity of the pool has been depleted or not is detected on the basis of the threshold and the used capacity. A policy for the capacity extension may be set in advance and the structure of storage media with respect to the additional capacity may be calculated according to the policy. 
     As shown in  FIG. 25 , the input screen  2300  includes a setting item  2310  for setting a threshold for the capacity of the storage tiered, a text box  2320  for inputting a threshold value, a setting item  2330  for setting the capacity extension policy, and various radio buttons. Examples of the radio buttons include a radio button  2340  for manually selecting the setting content of the capacity extension policy, a radio button  2350  for selecting a structural ratio of the same storage media as that of the storage tiered in operation, and a radio button  2360  for selecting a method for designating an application(s) in use and adjusting to the characteristics of the application(s). The input screen  2300  also includes, for example, a selection box  2370  for selecting the application(s), an OK button  1850  for commanding the execution of the processing, and a cancel button  1860  for terminating the screen without executing the processing. 
     The user can set the threshold for the capacity of the storage tiered by inputting the threshold to the setting item  2320  on the input screen  2300 . Furthermore, the user selects the capacity extension policy setting method by selecting various radio buttons. Also, when setting the capacity extension policy according to the characteristics of the application, the application to be used is selected from the selection box  2370 . The structural ratio calculation program  360  obtains, for example, the threshold and the capacity extension policy setting method, which are entered via the input screen  2300 , and calculates the structure of the capacity to be added to the storage tiered  2100  on the basis of the threshold and the setting method. 
     Referring back to  FIG. 22 , the structural ratio calculation program  360  obtains the IOPS information and IOPS distribution of the storage tiered  2100  from the storage apparatus  2000  (S 570 ). Specifically speaking, the structural ratio calculation program  360  issues an instruction to the dynamic tiered tontrol program  2060  of the storage apparatus  2000  to obtain the IOPS information of the storage tiered  2100  and create the IOPS distribution. 
     Subsequently, the structural ratio calculation program  360  refers to the storage media information table  370  and obtains information of the storage media in the storage apparatus  2000  (S 110 ). 
     The structural ratio calculation program  360  then judges whether or not the user authority is set to the storage media obtained in step S 110  (S 120 ). If it is determined in step S 120  that the user authority is set to the storage media, the structural ratio calculation program  360  obtains only information of the storage media to which the user authority is set (S 130 ). On the other hand, if it is determined in step S 120  that the user authority is not set to the storage media, the structural ratio calculation program  360  executes processing in step S 140 . 
     Then, the structural ratio calculation program  360  identifies the IOPS in excess of the IOPS limit for the existing volume  700  in the storage apparatus  600  and increases the number of IOPS (S 140 ). Next, the structural ratio calculation program  360  obtains the storage media with the lowest IOPS limit from among the information of the storage media obtained in step S 110  (S 150 ). 
     Next, the structural ratio calculation program  360  calculates the allocated capacity of the storage media selected in step S 150  (S 575 ). The processing for calculating the allocated capacity of the storage media in step S 575  will be explained later in detail. 
     Subsequently, the structural ratio calculation program  360  issues an instruction to a device management program  2030  of the storage apparatus  2000  to add the additional capacity of the storage media calculated in step S 575  to the storage tiered  2100  (S 580 ). 
     The structural ratio calculation program  360  may present the structure of the storage media to be added to the user before issuing the instruction to the storage apparatus  2000  to add the capacity to the storage tiered  2100 . For example, the structural ratio calculation program  360  displays a display screen  2400  shown in  FIG. 26  and presents the structure of the additional capacity of the storage tiered to the user. The display screen  2400  is a screen for presenting the storage media to be added to the storage tiered  2100  and the structure of the storage tiered  2100  after the addition to the user. The display screen  2400  includes a structure list  2410  of the storage media to be added to the storage tiered and a structure list  2420  of a storage tiered to be created after the addition. The display screen  2400  also includes an OK button  2430  for executing addition of the capacity to the storage tiered and a cancel button  2440  for terminating the screen without executing the addition of the capacity to the storage tiered. 
     The content to be displayed on the display screen  2400  may be designed so that the structure of the storage tiered is presented based on the structural ratio information table  390  by, for example, integrating several tiers in accordance with a constraint(s) of the dynamic tiered control. 
     Referring back to  FIG. 22 , the capacity growth state may be detected with respect to the capacity of the storage tiered  2100  and a judgment may be made according to the growth state in step  580  in the same manner as in the second embodiment. When the capacity growth state of the storage tiered  2100  indicates the growth completion, the migration processing shown in  FIG. 16  and  FIG. 17  is executed after step S 580  and excessively allocated storage media in light of the ideal IOPS distribution are deleted. 
     Next, the details of the processing for calculating the allocated capacity of the storage media in step S 575  will be explained. As shown in  FIG. 23 , the structural ratio calculation program  360  obtains the IOPS limit for the storage media selected in step S 150  from the storage media information obtained in step S 110  (S 600 ). 
     Next, the structural ratio calculation program  360  calculates the ideal capacity of pages that sufficiently satisfies the IOPS of the storage media selected in step S 150  on the basis of the IOPS distribution obtained in step S 570  and the TOPS limit for the storage media obtained in step S 610  (hereinafter referred to as the capacity (A)) (S 610 ). 
     Next, the structural ratio calculation program  360  calculates a ratio of the ideal capacity of the selected storage media to the data capacity of the storage tiered (hereinafter referred to as the ratio (B)) (S 620 ). 
     Then, the structural ratio calculation program  360  calculates the total capacity of the storage tiered and the additional capacity (hereinafter referred to as the total capacity (C)) (S 630 ). 
     Subsequently, the structural ratio calculation program  360  calculates the ideal capacity of the selected storage media in the storage tiered  2100  after addition of the capacity (hereinafter referred to as the ideal capacity (D)) on the basis of the ratio of the appropriate capacity of the selected storage media to the total capacity (C) (S 640 ). 
     Next, the structural ratio calculation program  360  subtracts the actual capacity of the storage tiered (hereinafter referred to as the actual capacity (DE)) from the ideal capacity (D), thereby calculating an ideal additional capacity (hereinafter referred to as the ideal additional capacity (F)) (S 650 ). 
     Then, the structural ratio calculation program  360  calculates the capacity by adding carry-over capacity to the ideal additional capacity (F) calculated in step S 650  (hereinafter referred to as the capacity (G)) (S 660 ). The carry-over capacity herein used means the capacity calculated in step S 720  described later; and when the retained capacity actually retained in the storage apparatus  2000  is insufficient as compared to the ideal additional capacity, such shortage is managed as the carry-over capacity to a lower-level tier. 
     Next, the structural ratio calculation program  360  obtains the retained capacity of the storage media selected in step S 150  (hereinafter referred to as the retained capacity (H)) (S 670 ). 
     Subsequently, as shown in  FIG. 24 , the structural ratio calculation program  360  compares the capacity (G) calculated in step S 660  and obtained by adding the carry-over capacity with the retained capacity (H) obtained in step S 670  (S 700 ). 
     If it is determined in step S 700  that the capacity (G) obtained by adding the carry-over capacity to the ideal additional capacity (F) is equal to or more than the retained capacity (F) of the storage media, the structural ratio calculation program  360  sets the retained capacity (H) of the storage media as the allocated capacity (S 710 ). Then, the capacity obtained by subtracting the retained capacity (H) of the storage media from the capacity (G) obtained by adding the carry-over capacity to the ideal additional capacity (F) is set as the carry-over capacity (hereinafter referred to as the carry-over capacity (I)) (S 720 ). 
     On the other hand, if it is determined in step S 700  that the retained capacity (H) of the storage media is larger than the capacity (G) to which the carry-over capacity is added, the capacity (G) obtained by adding the carry-over capacity to the ideal additional capacity (F) is set as the allocated capacity (S 730 ). 
     Next, the structural ratio calculation program  360  associates the allocated capacity of the storage media calculated in step S 720  or step S 730  with the selected storage media and stores them in the structural ratio information table  390  (S 740 ). 
     Then, the structural ratio calculation program  360  compares the capacity of the storage media which is written to the structural ratio information table  390  with respect to a page(s) to which the selected storage media is allocated, that is, a total of the allocated capacity (total allocated capacity), with the additional capacity requested for the storage tiered  2100  (S 750 ); and if the total allocated capacity is equal to or more than the requested additional capacity, the structural ratio calculation program  360  terminates the processing in step S 575  and executes the processing in step S 580  in  FIG. 22 . On the other hand, if it is determined in step S 750  that the total allocated capacity is less than the requested additional capacity, the structural ratio calculation program  360  executes processing in step S 760 . 
     Subsequently, the structural ratio calculation program  360  checks if the storage media with the next lower IOPS limit exists or not (S 760 ). If it is determined in step S 760  that the storage media with the next lower IOPS does not limit exist, the structural ratio calculation program  360  identifies the type and capacity of necessary storage media to satisfy the IOPS distribution, presents the screen for prompting the user to purchase the storage media ( FIG. 13 ) to the user (S 310 ), clears the content stored in the structural ratio information table  390 , and terminates the processing. On the other hand, if it is determined in step S 760  that the storage media with the next lower IOPS limit exists, the structural ratio calculation program  360  selects the storage media with the next lower IOPS (S 770 ) and repeats the processing in step S 600  and subsequent steps. 
     Regarding the method for calculating the ideal structure of the additional capacity, a calculation method on the basis that the IOPS distribution after adding the capacity to the storage tiered  2100  is similar to the IOPS distribution of the storage tiered in operation is used as described above from step S 610  to step S 650  for calculating the additional capacity of each storage media; however, the calculation method is not limited to such an example. For example, the ideal structure of the additional capacity may be calculated in accordance with the characteristics of the application(s) in use; and the processing step S 610  to step S 650  may not be executed as long as the ideal structure of the additional capacity can be calculated. Furthermore, the order of processing in step S 575  may be different from the order described earlier by adopting another method. 
     Next, a specific example of the above-described processing for calculating the structure of the additional capacity of the storage media will be explained. Like the aforementioned structural ratio calculation processing, the specific example shown in  FIG. 27  is also indicated on the basis that the IOPS distribution after addition of the additional capacity to the storage tiered  2100  is similar to the IOPS distribution of the storage tiered  2100  in operation. 
     An explanatory diagram  2500  in  FIG. 27  describes a case where, for example, the capacity of SSD is 15 GB, the capacity of SAS is 55 GB, and the capacity of SATA is 30 GB; and the structural ratio calculation program  360  receives an instruction to add the capacity of 50 GB to a storage tiered with a total capacity of 100 GB. In this case, it is assumed that information of the storage media obtained from the storage apparatus  2000  is also SSD, SAS, and SATA. The specific example of the structural ratio calculation processing in a case of calculation of the structure of additional storage media which is SAS will be explained. 
     Firstly, 50 GB of SAS is calculated as the ideal capacity (A) from the IOPS distribution of the storage tiered  2100  in step S 610  ( 2510 ). Next, in step S 620 , 50% of SAS is calculated as the ideal capacity ratio (B) ( 2520 ). Then, in step S 630 , 150 GB is calculated as the total capacity (C) of the storage tiered and the additional capacity ( 2530 ). 
     Subsequently, in step S 640 , 75 GB is calculated as the ideal capacity (D) of the SAS in the storage tiered  2100  after addition of the capacity on the basis of the appropriate capacity ratio of the SAS to the total capacity (C) ( 2540 ). 
     Next, 55 GB of the SAS is obtained as the actual capacity (E) of the storage tiered  2100  to be subtracted from the ideal capacity (D) calculated in step S 640  ( 2550 ) and 20 GB of the SAS is calculated as the ideal additional capacity (F) ( 2560 ). 
     Then, 25 GB of the SAS is calculated as the capacity (G) obtained by adding 5 GB of the carry-over capacity from the SATA to the ideal additional capacity (F) calculated in step S 650  ( 2570 ). 
     Next, 23 GB of the SAS is obtained as the retained capacity (H) of the selected storage media ( 2580 ). Then, the capacity (G) which is 25 GB of the SAS is compared with the retained capacity (H) which is 23 GB of the SAS; and since the capacity (G) is equal to or more than the retained capacity (H), the retained capacity (G) is set as the allocated capacity 23 GB of the SAS ( 2590 ). 
     Finally, if the capacity (G) is equal to or more than the retained capacity (H), a value 2 GB obtained by subtracting the retained capacity (H) from the capacity (G) is calculated as the capacity (I) to be carried over to the SSD ( 2600 ). 
     (3-3) Advantageous Effect of this Embodiment 
     In this embodiment as described above, as triggered by the reception of the notice of the capacity depletion of the storage tiered  2100  from the dynamic tiered tontrol program  2060  of the storage apparatus  2000 , the capacity to be added to the storage tiered  2100  can be obtained and the low-cost structure using the storage media held by the user can be calculated with respect to the additional capacity. 
     (4) Fourth Embodiment 
     (4-1) Hardware Configuration of Computer System 
     In this embodiment, a storage tiered is newly created based on the IOPS distribution of an existing logical volume in a storage apparatus in the same manner as in the first embodiment. In this embodiment, an externally connected storage apparatus exists besides storage media in the storage apparatus; and the structure of the storage tiered is calculated by externally connecting a logical volume in this external storage apparatus and using storage media information of the externally connected volume. The external connection herein used means a function that associates a logical volume, which is provided by another storage apparatus (external storage apparatus) connected to one storage apparatus, with a logical volume or a virtual volume provided by the one storage apparatus. In the following explanation, associating a logical volume of another storage apparatus with a logical volume of its own storage apparatus may be sometimes explained simply as external connection. 
     As shown in  FIG. 28 , a computer system  2700  according to this embodiment is constituted from, for example, a first storage apparatus  2730 , a second storage apparatus  2740 , a management computer  300 , and a host computer  500 . 
     A management interface  2780  for the second storage apparatus  2740  is connected to the management computer via a specified management network (for example, LAN)  190 . Consequently, the management computer  300  can communicate with the second storage apparatus  2740 . Incidentally, if the management network  190  is a LAN, each management interface  2780  can be, for example, a LAN card. 
     Furthermore, a communication port  2810  of the second storage apparatus  2740  is connected to the host computer  500  via a specified data communication network (for example, SAN)  200 . Consequently, the second storage apparatus  2740  can communicate with the host computer  500 . 
     Since the configuration of the management computer  300  and the host computer  500  according to this embodiment is the same as that of the management computer  300  and the host computer  500  according to the first embodiment, its detailed explanation has been omitted. 
     (4-2) Configuration of Storage Apparatus 
     Next, the configuration of the first storage apparatus  2730  and the second storage apparatus  2740  will be explained. Since the first storage apparatus  2730  and the second storage apparatus  2740  have almost the same configuration, only the configuration of the first storage apparatus  2730  will be explained. 
     As shown in  FIG. 29 , the first storage apparatus  2730  is constituted from, for example, a disk controller  2905 , volumes  3030 , an existing volume  3040 , and an external connection volume  3050 . In the following explanation, particularly the difference in the configuration from the storage apparatus  600  according to the first embodiment will be explained in detail. 
     A memory  2920  for the disk controller  2905  stores, for example, a device management program  2930 , a storage media management program  2940 , an external connection program  2950 , an IOPS counter  2960 , a dynamic tiered tontrol program  2970 , and an external connection volume information table  2980 . 
     Since the device management program  2930 , the device management program  2930 , the storage media management program  2940 , the IOPS counter  2960 , and the dynamic tiered tontrol program  2970  have almost the same functions as those of the device management program  630 , the storage media management program  640 , the IOPS counter  650 , and the dynamic tiered tontrol program  660  according to the first embodiment, its detailed explanation has been omitted. 
     After receiving an instruction from the structural ratio calculation program  360  of the management computer  300 , the external connection program  2950  detects a storage apparatus which can be externally connected to the first storage apparatus  2730 , obtains volume information of the detected storage apparatus, and externally connects that storage apparatus to the first storage apparatus  2730 . 
     The external connection volume information table  2980  is a table for managing information of an externally connected logical volume(s) and is constituted from a storage column  2981 , a storage media type column  2982 , a capacity column  2983 , and an laps limit column  2984  as shown in  FIG. 30 . The storage column  2981  stores an identifier or name of a storage apparatus which can be externally connected to the first storage apparatus  2730  and in which a logical volume that can be externally connected exists. The storage media type column  2982  stores information indicating the type of storage media of logical volumes which can be externally connected and belongs to each storage apparatus. However, there may be a case where the storage media type cannot be identified, depending on a storage apparatus to be externally connected. So, if the storage media type cannot be recognized, a hyphen is stored in the storage media type column  2982 . 
     Furthermore, the capacity column  2983  stores the capacity of each storage media. The IOPS limit column  2984  stores the maximum number of IOPS per page that can be processed by each storage media. The IOPS limit may be a predefined value or a value counted by the IOPS counter  2960  after actual transmission of test I/O by the device management program  2930  to the external connection volume  3050 . Furthermore, external connection volume information  3100  may be information of logical volumes existing in the storage apparatus which can be externally connected when extending the capacity, or information of an external connection volume(s) already mapped in the first storage apparatus. However, if the external connection volume information  3100  is the information of the logical volume(s) existing in the storage apparatus which can be externally connected, the information of the already mapped external connection volume(s) can be obtained at the same time when obtaining the storage media information in the storage apparatus. 
     Next, a storage media information table  3200  of the management computer  300  will be explained. The storage media information table  3200  is almost the same as the storage media information table  370  shown in  FIG. 1 , but the difference between them is that the storage media information table  3200  also stores information about externally connected volumes. In other words, the storage media information table  3200  is information obtained by integrating the external connection volume information table  3100  of the above-described first storage apparatus  2730  with the storage media information of the first storage apparatus  2730 . 
     The storage media information table  3200  is constituted from a tier order column  3210 , a storage media type column  3220 , a capacity column  3230 , an IOPS limit column  3240 , an externally connected storage media type column  3250 , and a use authority column  3260  as shown in  FIG. 31 . 
     The tier order column  3210  stores information indicating the tier order of storage media. The storage media type column  3220  stores information indicating the type of the storage media, for example, “SSD” or “SAS15K.” The capacity column  3230  stores information indicating the capacity of each storage media. The IOPS limit column  3240  stores information indicating the IOPS limit for each storage media. The IOPS limit is the maximum number of IOPS per page which can be processed by each storage media. The information stored in the IOPS limit column  3704  may be a predefined value or a value counted by the IOPS counter  2960  after actual transmission of test I/O by the device management program  2930  of the first storage apparatus  2730  to the existing volume  3040 . The externally connected storage media type column  3250  stores the type of storage media of the externally connected volume. However, there may be a case where the storage media type cannot be identified, depending on a storage apparatus to be externally connected. So, if the storage media type cannot be recognized, a hyphen is stored in the externally connected storage media type column  3250 . The use authority column  3705  stores information indicating the use authority of each user over each storage media. In the environment where the use authority is set to each storage media, for example, user A can select storage media to use only from an aggregate of storage media over which the user authority is granted to user A. Regarding an external connection volume, it is mapped to the first storage apparatus  2730  and the use authority is then set to that external connection volume. 
     (4-3) Structural Ratio Calculation Processing 
     Next, processing for calculating the structure of the storage tiered based on the IOPS distribution when the storage media information including a volume(s) which can be externally connected is included. The storage media structure calculation processing is executed by the structural ratio calculation program  360  of the management computer  300 . In the following explanation, the same step number is assigned to the processing of the same content as that of the structural ratio calculation processing according to the first embodiment and its detailed explanation has been omitted. 
     The structural ratio calculation processing according to this embodiment is executed by, for example, the administrator giving an instruction to the structural ratio calculation program  360  of the management computer  300  to create a storage tiered based on the IOPS distribution of the existing volume  3040 . 
     As shown in  FIG. 32 , the structural ratio calculation program  360  firstly obtains the IOPS distribution of the existing volume  3040  from the first storage apparatus  2730  (S 100 ). Next, the structural ratio calculation program  360  refers to the storage media information table  3200  and obtains the storage media information of the first storage apparatus  2730  (S 110 ). 
     Next, the structural ratio calculation program  360  checks with the external connection program  2950  of the first storage apparatus  2730  if any volume that can be externally connected exists in the second storage apparatus  2740  which can be externally connected (S 810 ). 
     If it is determined in step S 810  that a volume which can be externally connected exists in the second storage apparatus  2740 , the structural ratio calculation program  360  obtains information of the storage media which can be externally connected (S 820 ). Then, the structural ratio calculation program  360  stores the information obtained in step S 820  in the storage media information table of the first storage apparatus  2730  (S 830 ). On the other hand, if it is determined in step S 810  that a volume which can be externally connected does not exist in the second storage apparatus  2740 , the structural ratio calculation program  360  executes the processing in step S 120 . 
     Then, the structural ratio calculation program  360  judges whether the user authority is set to the storage media obtained in step S 110  and step S 810  (S 120 ). If it is determined in step S 120  that the user authority is set to the storage media, the structural ratio calculation program  360  obtains only information of the storage media to which the user authority is set (S 130 ). On the other hand, if it is determined in step S 120  that the user authority is not set to the storage media, the structural ratio calculation program  360  executes the processing in step S 140 . 
     Next, the structural ratio calculation program  360  identifies the IOPS in excess of the IOPS limit for the existing volume  700  in the storage apparatus  600  and increases the number of IOPS (S 140 ). Then, the structural ratio calculation program  360  obtains the storage media with the lowest IOPS limit from among the information of the storage media obtained in step S 110  (S 150 ). Subsequently, the structural ratio calculation program  360  calculates the allocated capacity of the storage media selected in step S 150  (S 160 ). 
     Then, the structural ratio calculation program  360  judges whether an external connection volume is included in the structural ratio information table  390  or not (S 900 ). If it is determined in step S 900  that an external connection volume is included in the structural ratio information table  390 , the volume which can be externally connected is externally connected to the first storage apparatus  2730  (S 910 ). If it is determined in step S 900  that an external connection volume is not included in the structural ratio information table  390 , the structural ratio calculation program  360  executes the processing in step S 170 . 
     Next, the structural ratio calculation program  360  creates a storage tiered based on the calculation result in step S 160  (S 170 ). Then, the structural ratio calculation program  360  copies data in descending order of the IOPS of the data, starting from the highest IOPS, to the storage tiered created in step S 170  (S 180 ). Incidentally, if there is a specified constraint(s) on the tier number representing the performance of the relevant tier in the storage tiered for the processing for creating the storage tiered which satisfies the above-described I/O frequency distribution, the structural ratio calculation program  360  may construct a tier with the performance equivalent to or higher than that of the tier number corresponding to the relevant constraint. Furthermore, If there is a specified constraint(s) on the number of storage media constituting a storage tier with respect to the processing for creating the storage tiered which satisfies the above-described I/O frequency distribution, the structural ratio calculation program  360  may select the storage media as many as or less than the number of storage media corresponding to the constraint. 
     (4-4) Advantageous Effect of this Embodiment 
     If the host computer  500  issues a request to create a storage tiered and a volume which can be externally connected is included in the storage media held by the user, a low-cost storage tiered can be created according to this embodiment as described above. 
     INDUSTRIAL APPLICABILITY 
     The present invention can be applied to a wide variety of computer systems that configure a storage tiered by using storage media held by a user. 
     REFERENCE SIGNS LIST 
     
         
           100  Computer system 
           190  Management network 
           200  Data communication network 
           300  Host computer 
           310  Input device 
           320  Output device 
           330  Processor 
           340  Disk device 
           350  Memory 
           360  Structural ratio calculation program 
           370  Storage media information table 
           380  IOPS information table 
           390  Structural ratio information table 
           600  Storage apparatus 
           605  Disk controller 
           610  Processor 
           620  Memory 
           630  Device management program 
           640  Storage media management program 
           650  Counter 
           660  Dynamic tiered control program