Patent Publication Number: US-9411746-B2

Title: Computer system, computer and method for performing thin provisioning capacity management in coordination with virtual machines

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS 
     This application is a Continuation of U.S. application Ser. No. 14/157,029, filed Jan. 16, 2014 (now U.S. Pat. No. 9,058,125), incorporated herein by reference in its entirety, which is a Continuation of U.S. application Ser. No. 12/745,842 (National Stage of PCT/JP2010/000705), filed Jun. 2, 2010 (now U.S. Pat. No. 8,656,136), incorporated herein by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The present invention relates to management of a computer system which includes a storage system and a server computer. 
     BACKGROUND ART 
     Storage capacity virtualization technology called “Thin provisioning technology” is known. Thin provisioning technology is disclosed in Patent Literature 1. 
     CITATION LIST 
     Patent Literature 
     [PTL 1] 
     Japanese Patent Application Laid-open No. 7613896. 
     SUMMARY OF INVENTION 
     Technical Problem 
     When a server computer provides virtual machines by means of a server virtualization program, the virtual machines can be created and deleted more flexibly. However, if virtual volumes are provided using thin provisioning technology, then it is not possible readily to perform capacity management of thin provisioning in coordination with the creation and deletion of virtual machines. 
     Therefore, the object of the present invention is to carry out capacity management of thin provisioning in accordance with the creation and deletion of virtual machines. 
     Solution to Problem 
     In the computer system according to the present invention, a storage system provides storage level virtual volumes based on thin provisioning technology, to a physical server on which a virtual machine is defined. The storage system releases the area of the logical volume corresponding to the storage level virtual volume accessed by a virtual machine specified to be deleted, on the basis of storage level virtual volume conversion information which is managed by the storage system. 
     Advantageous Effects of Invention 
     According to the present invention, capacity management of thin provisioning can be carried out readily in accordance with the creation and deletion of virtual machines. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a diagram showing the configuration of a computer system according to a first embodiment of the present invention. 
         FIG. 2  is a diagram showing the details of information and programs stored in the memory  4050   c  of a management server  1000 . 
         FIG. 3  is a diagram showing the configuration of a storage control program  2500 . 
         FIG. 4  is a diagram illustrating thin provisioning carried out in a storage system  2000 . 
         FIG. 5  is a diagram illustrating thin provisioning carried out in a physical server  3000 . 
         FIG. 6  is a block diagram showing storage level pool configuration information  1400 . 
         FIG. 7  is a block diagram showing storage level virtual volume configuration information  1500 . 
         FIG. 8  is a block diagram showing port/LUN correspondence information  1600 . 
         FIG. 9  is a block diagram showing server level pool configuration information  1700 . 
         FIG. 10  is a block diagram showing storage level virtual volume configuration information  1800 . 
         FIG. 11  is a block diagram showing the end-to-end capacity leverage rate information  1900 . 
         FIG. 12  is a block diagram showing initial settings information  1910 . 
         FIG. 13  shows a display screen of the end-to-end capacity leverage ratio. 
         FIG. 14  is a flow diagram of processing carried out by the management program  1200  according to a first embodiment. 
         FIG. 15  is a flow diagram of the processing in step S 103  in  FIG. 14 . 
         FIG. 16  is a flow diagram of storage configuration change processing. 
         FIG. 17  is a flow diagram showing processing carried out by a management program using a callback interface. 
         FIG. 18  is a flow diagram of storage configuration change processing in a case where the management program  1200  is provided with a callback interface. 
         FIG. 19  is a flow diagram of a callback process. 
         FIG. 20  is a flow diagram of the processing in step S 503  in  FIG. 17 . 
         FIG. 21  is a flow diagram showing the processes of setting up and adding a storage level virtual volume  2230  to a server level pool  3210 . 
         FIG. 22  is a flow diagram of processing carried out when the server virtualization program has received a read request from a virtual machine to a server level virtual volume. 
         FIG. 23  is a flow diagram of processing carried out when the server virtualization program has received a write request from a virtual machine to a server level virtual volume. 
         FIG. 24  is a flow diagram of processing for reading data from the storage level virtual volume. 
         FIG. 25  is a portion of a flow diagram showing a process of writing data to a storage level virtual volume  2230 . 
         FIG. 26  is a flowchart showing a process of adding a volume  2210  to the storage level pool  2220 . 
         FIG. 27  is a flow diagram of cause location identification processing. 
         FIG. 28  is a diagram showing the details of information and programs stored in the memory  4050   a  of a storage controller  210 . 
         FIG. 29  is a diagram showing the details of information and programs stored in the memory  4050   b  of a physical server  3000 . 
         FIG. 30  is a block diagram showing storage level pool information  11000 . 
         FIG. 31  is a block diagram showing storage level virtual volume information  12000 . 
         FIG. 32  is a block diagram showing volume information  13000 . 
         FIG. 33  is a block diagram showing storage internal mapping information  14000 . 
         FIG. 34  is a block diagram showing server level pool information  15000 . 
         FIG. 35  is a block diagram showing server level virtual volume information  16000 . 
         FIG. 36  shows one example of a hierarchy relationship of storage areas. 
         FIG. 37  shows one example of a cause location display screen. 
         FIG. 38  shows one example of a screen where the end-to-end capacity leverage ratio and the free capacity ratio are displayed side by side. 
         FIG. 39  is the remainder of a flow diagram showing a process of writing data to a storage level virtual volume  2230 . 
         FIG. 40  is the remainder of a flow diagram showing a process of writing data to a server level virtual volume  3220 . 
         FIG. 41  is a first schematic diagram of the deletion of a virtual machine. 
         FIG. 42  is a second schematic diagram of the deletion of a virtual machine. 
         FIG. 43  is a third schematic diagram of the deletion of a virtual machine. 
         FIG. 44  is a flow diagram showing a process of deleting a virtual machine. 
         FIG. 45  is a diagram of a display screen showing the deletion of virtual machines and related capacities. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Below, embodiments of the present invention are described with respect to the accompanying drawings. The definitions of the terms used in the description of the embodiments are as indicated below. For other terms, generic definitions can be applied. Furthermore, in the following description, processes executed by a computer program are actually carried out by a processor which executes the computer program. 
     “Leverage ratio” is the ratio of the capacity of a virtual storage area corresponding to a physical storage area, with respect to the capacity of the physical storage area. In the present embodiment, there are leverage ratios of a plurality of types. For example, the leverage ratio of a first type is the ratio of the total capacity of one or more server level pools corresponding to a storage level pool, with respect to the capacity of the storage level pool. The leverage ratio of a second type is the ratio of the total capacity of one or more server level virtual volumes corresponding to a storage level pool, with respect to the capacity of the storage level pool. In the following description, the second type of leverage ratio, in particular, is called “end-to-end capacity leverage ratio”. 
     “Volume” means a logical storage area (logical volume) which is provided on the basis of one or more physical storage devices (for example, a hard disk drive or flash memory). A volume is provided on the basis of a storage space of a RAID (Redundant Array of Independent (or Inexpensive) Disks) group, for example. The RAID group contains a plurality of physical storage devices, and data is stored in accordance with prescribed RAID levels. 
     “Storage level virtual volume” means a virtual volume which is provided by the storage controller. The whole area of a storage level virtual volume (the area is also called a storage region and hereinafter, may be referred to as a storage level virtual volume address area or a low-level address area (LL-AA)), does not necessarily have to be allocated to the storage region of a storage device or volume (hereinafter, this storage region may be referred to as a low-level storage area (LL-SA)). More specifically, for instance, all or a portion of the area (LL-AA) of the storage level virtual volume is not initially allocated with the area (LL-SA) in one or more volumes belonging to a storage level pool. In other words, initially, for example, a portion of the area (LL-SA) of a storage level pool may be allocated to an area (LL-AA) of a portion of the storage level virtual volume. Here, “initially” means, for example, immediately after a storage level virtual volume has been defined, or immediately after a storage level virtual volume has been defined and has become accessible from a physical server. The storage system sends the capacity of the storage level virtual volume to the physical server on the basis of storage level virtual volume information which represents the capacity of the storage level virtual volume. The data format, such as the data structure, may differ, and may be different due to rounding down, or the like, between the capacity of the storage level virtual volume which is managed internally in the storage system and the capacity of the storage level virtual volume which is sent to the physical server by SCSI protocol, or the like. Of course, the capacity of the storage level virtual volume which is managed inside the storage system and the capacity of the storage level virtual volume which is sent to the physical server may be the same. 
     “Server virtualization program” is a program which constructs a virtual server system by virtualizing the physical resources of a physical server. The server virtualization program is, for example, a hypervisor. Furthermore, the physical resources are, for example, a processor (for instance, a microprocessor), a storage resource (for instance, a memory), and a communications interface apparatus (for instance, an HBA (Host Bus Adapter)). 
     A “virtual machine” is a virtual computer which is provided by a server virtualization program. By means of a server virtualization program, it is possible to construct a system in such a manner that a plurality of computers operate effectively on a single physical server. Each of these effective computers is a virtual machine (may be referred to as VM). In a virtual machine, for example, a computer program, such as an OS (Operating System), or the like, is carried out virtually. 
     “Server level pool” is a storage area constructed from one or more storage level virtual volumes allocated from the storage system by the server virtualization program. The server level pool is used from a virtual machine via a server level virtual volume. More specifically, if data is being written from a virtual machine to a server level virtual volume, then the area of a portion of the server level pool (more accurately, the volume or virtual machine provided by the storage system included in the server level pool) (this area may be referred to hereinafter as a high-level storage area (HL-SA)) is allocated to the area of the server level virtual volume specified as the write destination for that data (hereinafter, this area is referred to as a server level virtual volume area, or a high-level address area (HL-AA)). If the virtual volume is included in the server level pool, then HL-SA indicates the same object as LL-AA. However, the management units differ as described hereinafter. Thereupon, a write request indicating an area (HL-SA) inside the storage level virtual volume which corresponds to the area (HL-AA) of the allocated portion is sent to the storage system that provides that storage level virtual volume, from the physical server (for example, from the server virtualization program executed on the physical server). In response to this write request, the storage controller of the storage system allocates a portion of the area inside the storage level pool (LL-SA) to the area indicated in the write request (the area inside the storage level virtual volume (LL-AA)), and writes data to the allocated area (LL-AA). When reference is made below to “write data to the LL-AA”, in practice this means writing the data to the LL-SA which corresponds to the LL-AA. Furthermore, in the following description, reference to “the area of a volume or virtual volume provided by a storage system included in the server level pool” is abbreviated to the expression “area of the server level pool”. 
     “Server level virtual volume” is a virtual volume which is constructed by a server virtualization program. The whole of the storage area (HL-AA) of the server level virtual volume does not necessarily have to be allocated to a physical storage area (HL-SA). The storage area of the server level virtual volume is accessed by a virtual machine. 
     “Storage level pool” is a pool made up of one or more volumes. The area (LL-SA) of one portion of the storage level pool is allocated as a write destination area (LL-AA) from the physical server, in the storage level virtual volume. The storage level pool may be a group (a virtual pool) of a plurality of pools belonging to one or more volumes. In the description given below, reference to “area of a volume included in the storage level pool” is abbreviated to the expression “area of the storage level pool”. 
       FIG. 36  shows one example of a hierarchy relationship of storage areas. In  FIG. 36 , a virtual machine is represented as “VM”, a volume is represented as “VOL”, a storage level pool is represented as “LLP” which is an abbreviation of “low-level pool”, a storage level virtual volume is represented as “LL-VVOL” which is an abbreviation of “low-level virtual volume”, a server level pool is represented as “HLP” which is an abbreviation of “high-level pool”, and a server level virtual volume is represented as “HL-VVOL” which is an abbreviation of “high-level virtual volume”. This method of representation is also employed as appropriate in the other drawings. 
     According to this example, there are a plurality of storage level pools (for example, storage level pools  1 ,  2 ), and a storage area topology having a tree structure is constructed on the basis of these respective storage level pools. The constituent elements of the storage area topology are, stated in order from the lower level, storage level pools, storage level virtual volumes, server level pools and server level virtual volumes. According to this example, the following storage areas (A) to (D) correspond to the storage level pool  1 : 
     (A) storage level virtual volume  1  and  2 ; 
     (B) server level pools  1  and  2  which correspond respectively to the storage level virtual volumes  1  and  2 ; 
     (C) server level virtual volume  1  which corresponds to server level pool  1  (server level virtual volume  1  to which a portion of storage area is allocated from the server level pool  1 ); and 
     (D) server level virtual volumes  2  and  3  which correspond to the server level pool  2 . 
     In other words, according to this example, the server level virtual volumes  1  to  3  correspond to the storage level pool  1 , these server level virtual volumes  1  to  3  being constituent elements of the storage area topology based on the storage level pool  1 . 
     In the embodiment described below, it is possible to calculate the end-to-end capacity leverage ratio for each storage area topology, in other words, for each storage level pool. This is because, for each storage level pool, it is possible to identify the storage area topology forming the basis of that storage level pool, in other words, to identify the corresponding server level virtual volumes. 
     As shown in  FIG. 36 , a server level pool may share a plurality of physical servers, for example, physical servers  3  and  4 . In this case, even if a virtual machine  3  in the physical server  3  is migrated to the physical server  4  as indicated by the dotted line, for example, the end-to-end capacity leverage ratio of the storage level pool  2  does not change. This is because the migration of the virtual machine  3  means that the server level virtual volume  4  which was mounted on the virtual machine  3  is also migrated to the physical server  4 , but no actual change occurs in the capacity of that server level virtual volume  4 . In other words, the end-to-end capacity leverage ratio of the storage level pool  2  changes in cases where a configuration change which alters the total capacity of the server level virtual volumes  4  and  5  corresponding to the storage level pool  2  (or a configuration change which alters the capacity of the storage level pool  2 ) has been carried out. 
     A server level virtual volume includes a plurality of HL-AA, but the size of each HL-AA may be a common size corresponding to the server level virtual volume. The server level pool includes a plurality of HL-SA, but the sizes of each HL-SA may be a common size corresponding to the server level pool, or respectively different sizes. A storage level virtual volume includes a plurality of LL-AA, but the size of each HL-AA may be a common size corresponding to the storage level virtual volume. The storage level pool includes a plurality of LL-SA, but each LL-SA may have a common size corresponding to the storage level pool. In this configuration, the correspondences between pages may be managed by means of a table, or the like, or may be determined by calculation. 
     When a program executed on a virtual machine has issued a write request indicating a certain HL-AA in a sever level virtual volume, then if an HL-SA is not allocated to that HL-AA, an unallocated HL-SA is duly allocated from the server level pool corresponding to that sever level virtual volume. A write request indicating the LL-AA corresponding to the allocated HL-SA is then sent to the storage system  2000  from the physical server  3000 . In the storage system  2000 , if an LL-SA has not be allocated to that LL-AA, then an unallocated LL-SA is allocated to the LL-AA, from the storage level pool corresponding to the storage level virtual volume having the LL-AA. Data corresponding to the write request is then written to the LL-SA. If the LL-SA is based on a plurality of PDEVs, for example, then data is stored in the plurality of PDEVs in accordance with a prescribed RAID level, for example. 
     First Embodiment 
     In the first embodiment, a management server gathers virtual volume information for the storage system and virtual volume information for the physical servers, analyzes the virtual volume information of the storage system and the virtual volume information of the physical server, and indicates the end-to-end capacity leverage ratio to the administrator (for example, storage administrator) on the basis of these analysis results. The details of this are described below. 
     1. Configuration of Computer System 
       FIG. 1  is a diagram showing the configuration of a computer system according to a first embodiment of the present invention. 
     The computer system comprises a storage system  2000 , a physical server  3000  and a management server  1000 . At least one of the storage system  2000 , the physical server  3000  and the management server  1000  may be provided in plural fashion. 
     The storage system  2000  and the physical server  3000  are mutually connected via a communications network, for example, a SAN  5000  or a LAN  5010 . The management server  1000  connects the storage system  2000  and the physical server  3000  via a communications network, for example, a LAN  5010  or a SAN  5000 . 
     &lt;1-1. Configuration of Storage System&gt; 
     The storage system  2000  comprises a plurality of PDEVs (physical storage devices)  2100   a  and a plurality of storage controllers (CTL)  2010 . The PDEVs  2100   a  and the storage controllers  2010  are connected to each other by means of an internal network or bus, for example. The storage controller  2010  stores data in a storage area on the basis of the PDEVs  2100   a.    
     The PDEVs  2100   a  are disk type storage media drives (for example, hard disk drives) and store data in accordance with write requests received by the storage system  2000  from the physical server  3000 . The PDEVs  2100   a  may also be flash memory drives, for instance. It is also possible to provide one PDEV  2100   a  only. 
     The storage controller  2010  is an apparatus which controls the operation of the storage system  1000 . The storage controller  2010  comprises an internal network. The internal network is connected, for example, to a storage port  4020   a , a processor  4010   a  (for example, CPU) and a memory  4050   a . Storage controllers  2010  are connected to each other via the internal network. Furthermore, the storage controllers  2010  and respective PDEVs  2100   a  are connected to each other by a plurality of back-end networks. It is also possible to provide one storage controller  2010  only. 
     The storage port  4020   a  is an interface which is connected to the storage system  2000  and the management server  7000  via a network, such as a SAN  5000 . 
     The processor  4010   a  carries out processing of various types by executing a program stored in the memory  4050   a.    
     The memory  4050   a  is formed by a RAM (Random Access Memory), for example, and stores programs to be executed by the processor  4010   a  and information required by the processor  4010   a , and the like. More specifically, for example, a storage control program  2500  is stored in the memory  4050   a  of the storage controller  2010 , and controls the storage controller  2010  on the basis of management operation requests received from the management server  1000 . A management operation request is a request for operating the storage system  2000 , for example, a volume construction request, storage level pool construction request, or the like. The memory  4050   a  may be employed as a cache memory in which data input to or output from the PDEVs  2100   a  is stored temporarily. 
     The internal networks in the physical server  3000  and the storage system  2000  desirably have broader bandwidth than the transmission bandwidth of the storage port  4020   a , and all or a portion thereof may be substituted by bus or switch type networks. Furthermore, in  FIG. 1 , one storage port  4020   a  is present in the storage controller  2010 , but in actual practice, a plurality of storage ports  4020   a  may be present in the storage controller  2010 . The storage controller  2010  may be formed by a plurality of components. Similarly, the memory  4050   a  may also be formed by a plurality of components. 
     As described below, the storage system  2000  forms one or more volumes which belong to a storage level pool, for example. The storage level pool may belong to the storage system  2000 , or may belong to a system other than the storage system  2000  (for example, a system interposed between the storage system  2000  and the physical server  3000  (for instance, a switching apparatus)). 
     A storage system may be one storage apparatus, or a group of a plurality of storage apparatuses. For example, a volume (VOL) managed by a certain storage apparatus may be a VOL based on a PDEV contained in another storage apparatus. 
     The whole area (LL-AA) of one or more volumes may have been allocated to the area (LL-SA) of a storage device included in a storage system, or a portion of the area (LL-AA) of one or more volumes may not have been allocated to the area (LL-SA) of the storage device. 
     &lt;1-2. Configuration of Physical Server&gt; 
     The physical server  3000  is one example of a server computer, and comprises a processor  4010   b , a memory  4050   b  and an HBA  4020   b . The processor  4010   b , the memory  4050   b  and the HBA  4020   b  are connected to each other via an internal network. 
     The processor  4010   b  carries out processing of various types by executing a program stored in the memory  4050   b . For example, the processor  4010   b  can input or output (write or read) data to or from one or more storage level virtual volumes  2230  provided by the storage system  2000 , by sending an I/O request (write request or read request) to the storage system  2000 . 
     The memory  4050   b  stores programs which are executed by the processor  4010   b  and information required by the processor  4010   b , and the like. The memory  4010   b  may be a semiconductor memory or storage device, or a combination of these. The memory  4050   b  stores a server virtualization program  3200 . 
     The HBA  4020   b  is an interface which is connected to the storage system  2000  via a network, such as a SAN  5000 , LAN  5010 , or the like. More specifically, for example, the HBA  4020   b  outputs I/O requests from the processor  4010   b  to the storage system  2000 . 
     The server virtualization program  3200  constructs a virtual server environment (virtual machine) from the physical resources belonging to the physical server  3000 . 
     &lt;1-3. Configuration of Management Server&gt; 
     The management server  1000  is a computer which comprises a processor  4010   c , a memory  4050   c , a management program  1200 , and a NIC (Network Interface Card)  4040   c . The processor  4010   c , the memory  4050   c , the PDEV  2100   c  and the NIC  4040   c  are connected to each other via an internal network. 
     The processor  4010   c  carries out processing of various types by executing a program stored in the memory  4050   c . For example, the processor  4010   c  controls the allocation of storage level virtual volumes  2230  to the physical server  3000  as executed by the storage system  2000 , by sending a management request to the storage system  2000 . The management request may include a remote transfer request or a copy control request, or the like. 
     The memory  4050   c  stores programs which are executed by the processor  4010   c  and information required by the processor  4010   c , and the like. For example, a management program  1200  is stored in the memory  4050   c . The memory  4050   c  may be a semiconductor memory or storage device, or a combination of these. 
     The NIC  4040   c  is an interface which is connected to the storage system  2000  via a network, such as a LAN  5010 , or the like. 
     The management server  1000  may comprise an input/output device  4060 . The input/output device  4060  inside the management server  1000  is also connected to the internal network. 
     Examples of an input/output device  4060  are a display, a keyboard and a pointer device, but devices other than these may also be used. Furthermore, as an alternative to an input/output device  4060 , a serial interface or Ethernet (registered trademark) interface may be used as an input/output device  4060 . Moreover, a display computer comprising a display, keyboard or pointer device may also be connected to this interface. Display information may be sent to a display computer and input information may be received from a display computer. By this means, a display can be provided on the display computer and by receiving an input, an input operation to the input/output device  4060  can be performed. 
     The management program  1200  manages the storage system  2000 . More specifically, for example, the management program  1200  performs operations, such as managing the volume configuration, managing the storage level pool configuration, managing the storage level virtual volume configuration, instructing volume allocations of various types, and so on. 
     The management server  1000  may be divided into a device which manages the storage system  2000  and a device which manages the physical servers  3000 . More specifically, for instance, the management server  1000  is one example of a management system. The management system comprises one or more computers, for example, a management computer, or a combination of a management computer and a display computer. More specifically, if the management computer shows display information, for example, then the management computer forms a management system. Furthermore, in order to increase the speed and reliability of processing, it is also possible to achieve functions similar to those of the management computer by means of a plurality of computers, and in this case, the plurality of computers (also including a display computer if display is performed by a display computer) form a management system. 
     2. Details of Storage 
       FIG. 28  is a diagram showing the details of information and programs stored in the memory  4050   a  of the storage controller  210 . 
     The memory  4050   a  stores, for example: storage level pool information  11000 , storage level virtual volume information  12000 , volume information  13000 , storage internal mapping information  14000  and a storage control program  2500 . 
     The storage level pool information  11000  is information relating to storage level pools. 
     The storage level virtual volume information  12000  is information relating to storage level virtual volumes. 
     The volume information  13000  is information relating to volumes. 
     The storage internal mapping information  14000  is information which indicates the mapping of storage areas of various types (volumes, storage level pools, storage level virtual volumes) which are managed by the storage system  2000 . 
     The storage control program  2500  is a program in which processing relating to the control of the storage system  2000  is defined. The storage control program  2500  comprises, for example, a storage virtualization module  2501 , a storage configuration management module  2502  and a command control module  2503 . The respective modules included in the storage control program  2500  do not necessarily have to be modules of a single program, and may respectively be separate program codes. 
     &lt;2-1. Description of Information Belonging to Storage System&gt; 
     &lt;2-1-1. Description of Storage Level Pool Information&gt; 
       FIG. 30  is a block diagram showing storage level pool information  11000 . 
     The storage level pool information  11000  includes, for example, for each storage level pool, information relating to the storage level pool, as well as information relating to the volumes belonging to the storage level pool and information relating to the storage level virtual volumes to which storage area is allocated from the storage level pool. More specifically, for example, the storage level pool information  11000  is a table, which contains, for each storage level pool, a record of the following attribute values: a storage level pool identifier  11001 , a storage level pool capacity  11002 , a storage level pool free capacity  11003 , volume identifiers  11004 , storage level virtual volume identifiers  11005 , a storage level virtual volume total capacity  11006 , an LL-SA size  11007  and an unallocated LL-SA identifier list  11008 . 
     The storage level pool identifier  11001  is an identifier which is allocated to the storage level pool  2220  by the storage virtualization module  2501 . 
     The storage level pool capacity  11002  is the capacity of the storage level pool. 
     The storage level pool allocated capacity  11003  is the total capacity of the area, out of the capacity of the storage level pool, which has been allocated to storage level virtual volumes  2230  by the storage control program  2500 . 
     The volume identifiers  11004  are identifiers of volumes belonging to the storage level pool. A volume belonging to the storage level pool means a volume which has been set so as to belong to the storage level pool by the storage virtualization module  2501 . 
     The storage level virtual volume total capacity  11005  is the sum value of the capacities of all of the storage level virtual volumes corresponding to the storage level pool. 
     The LL-SA size  11007  is a value indicating the management unit length (more specifically the unit length which is allocated or released) of the area (LL-SA) of a volume included in the storage level pool. 
     The unallocated LL-SA identifier list  11008  is a list of the identifiers of the areas (LL-SA) which are not allocated to a storage level virtual volume that has been associated with the storage level pool. In the examples of identifiers shown in the drawings, an offset number from a list stored in the volume identifier  11004  is stated before the colon “:”, and an offset number from the start of the area (LL-SA) of the volume indicated by the volume identifier  11004  and the offset number is stated after the colon. The areas (LL-SA) are created by dividing up the volume from the start, by the LL-SA size  11007 , and offset numbers 0, 1, . . . , are allocated to the areas in order from the start of the area (LL-SA). Taking as an example the identifier “01:002” of the unallocated LL-SA in the storage level pool “STPOOL- 1 ”, the “01” before the colon indicates the identifier of the next volume from the start, and therefore the volume identifier corresponds to “STLDEV- 2 ”, while the “002” after the colon indicates the third area (LL-SA) from the start of STLDEV- 2 . Incidentally, since the LL-SA size of the STPOOL- 1  is 100 MB (where 1 M is 1024 K, and 1 K is 1024), then supposing that data is addressed based on units of 512 byte blocks, this third area (LL-SA) from the start will range from the 400 k block to the (600 k−1) block. Below, unless expressly stated otherwise, block addresses are based on units of 512 byte blocks, 1 M is 1024 K, and 1 K is 1024. 
     Provided that the storage level pool information  11000  contains attribute values relating to a storage level pool, a data structure other than a table may be employed, and attribute values relating to a storage level pool other than the attribute values described above may also be included. Furthermore, the storage level pool information  11000  may omit a portion of the attribute values described above, apart from the storage level pool identifier. Furthermore,  FIG. 31  shows an example of values stated in byte units, but it is also possible to use other units (for example, SCSI block length or another area management unit length, etc.) This point is common to the information held by the computer system. 
     Furthermore, as can be seen from  FIG. 30 , the storage level pool capacity  11002  is not necessarily the same as the storage level virtual volume total capacity  11005 . This is because the storage level pool may be formed by an area of a portion of one or more volumes belonging to the storage level pool. 
     &lt;2-1-2. Storage Level Virtual Volume Information&gt; 
       FIG. 31  is a block diagram showing storage level virtual volume information  12000 . 
     The storage level virtual volume information  12000  includes, for each storage level virtual volume: information relating to the storage level virtual volume, and information relating to the storage level pool which is the allocation source of the area allocated to that storage level virtual volume. More specifically, for example, the storage level virtual volume information  12000  is a table which contains, for each storage level virtual volume, a record of the following attribute values: a storage level virtual volume identifier  12001 , a storage level virtual volume capacity  12002 , a storage level virtual volume allocated capacity  12003 , a storage level pool identifier  12004 , a storage level pool capacity  12005  and a port number/LUN (Logical Unit Number)  12006 . Moreover, the storage level virtual volume information  12000  also includes storage level area conversion information  12007  (expressed in the drawing as “LL-area conversion information”). 
     The storage level virtual volume identifier  12001  is an identifier which is allocated to the storage level virtual volume by the storage virtualization module  2501 . 
     The storage level virtual volume capacity  12002  is the capacity of the storage level virtual volume set by the storage virtualization module  2501 . 
     The storage level virtual volume allocated capacity  12003  is the total capacity of the area, out of the storage level virtual volume capacity  1502 , which has been allocated to the storage level virtual volume from the storage level pool by the storage control program  2500 . 
     The storage level pool identifier  12004  is an identifier of the storage level pool  2220  which is the allocation source of the area allocated to the storage level virtual volume. 
     The storage level pool capacity  12005  is the capacity of the storage level pool. 
     The port number/LUN  12006  is the port number and LUN corresponding to the storage level virtual volume. 
     The storage level area conversion information  12007  is information that includes the identifiers of the areas (LL-SA) of the storage level pool which have been allocated to each area (LL-AA) of the storage level virtual volumes. An area (LL-AA) for which the area (LL-SA) is marked as “unallocated” means that an area (LL-SA) has not been allocated to the corresponding area (LL-AA). The storage level area conversion information  12007  is created with all (or a portion) of the LL-AA set to “unallocated” immediately after definition of the corresponding storage level virtual volume, and as described below, areas (LL-SA) are allocated in accordance with an initial write request which covers the range of a portion or all of the areas (LL-AA) and the write data of the write request is saved in the areas (LL-SA). 
     In the example illustrated, the storage level area conversion information  12007  is expressed in the form of a list, and identifiers which respectively indicate an area (LL-SA) allocated to an area (LL-AA) (or which indicate the value “unallocated”) are stored in sequence from the area (LL-AA) at the start of the storage level virtual volume. 
     If the block address specifying an area (LL-AA) is the [Y] block address, then the address of the 512 byte block of the corresponding area (LL-SA) is determined as follows. 
     [LL-SA offset]=value obtained by dividing [Y] by [LL-SA size  11007  of corresponding storage level pool] (rounded down to nearest integer). 
     [LL-SA offset internal address]=remainder obtained by dividing [Y] by [LL-SA size  11007  of corresponding storage level pool] 
     [Volume where corresponding LL-SA resides]=value before colon [:] in identifier of [LL-SA offset] in list  12007 . Reference to the “x offset value in the list” means the (x+1)th value from the top of the list. 
     [Address in volume where corresponding LL-SA resides]=(value after[:] in [LL-SA offset identifier] in list  11008 ])×[LL-SA size  11007  of corresponding storage level pool]+[LL-SA offset internal address]). 
     Therefore, when an I/O request specifying the 501 K block address of the storage level virtual volume STVVOL- 1  is received from the physical server  3000 , the following calculation is carried out. 
     LL-SA offset=2 
     LL-SA offset internal address=101 K block 
     Volume where corresponding LL-SA resides=02 (identified as STLDEV- 8  by referring to the volume identifier  11004  in  FIG. 30 ) 
     Address in volume where corresponding LL-SA resides=1701 K block 
     Provided that the storage level virtual volume information  12000  contains attribute values relating to a storage level virtual volume, a data structure other than a table may be employed, and attribute values relating to a storage level virtual volume other than the attribute values described above may also be included. Furthermore, the storage level virtual volume information  12000  may omit a portion of the attribute values described above, apart from the storage level virtual volume identifier  12001 . 
     &lt;2-1-3. Volume Information&gt; 
       FIG. 32  is a block diagram showing volume information  13000 . 
     The volume information  13000  contains, for each volume, information relating to a volume and information on the storage level pool to which the volume belongs. More specifically, for example, the volume information  13000  is a table which contains, for each volume, a record of the following attribute values: a volume identifier  13001 , a volume capacity  13002 , PDEV identifiers  13003 , and a storage level pool identifier  13004 . 
     The volume identifier  13001  is an identifier which is allocated to the volume by the storage virtualization module  2501 . 
     The volume capacity  13002  is the capacity of the volume. A volume is constructed, for example, by the storage virtualization module  2501  grouping together the storage area of one of more PDEVs  2100   a . The storage area of the volume is mapped and distributed to the storage area of one or more PDEVs  2100   a  under control implemented by the storage controller  4050 . 
     The PDEV identifier  13003  is an identifier that has been allocated to a PDEV  2100   a  based on the volume by the storage virtualization module  2501 . In other words, the PDEV identifiers  13003  are the identifiers of the PDEVs  2100   a  which form the basis of the volume. 
     The storage level pool identifier  13004  is an identifier of the storage level pool  0  to which the volume belongs. 
     Provided that the volume information  13000  contains attribute values relating to a volume, a data structure other than a table may be employed, and attribute values relating to a volume other than the attribute values described above may also be included. Furthermore, the volume information  13000  may omit a portion of the attribute values described above, apart from the volume identifier  13001 . 
     &lt;2-1-4. Storage Internal Mapping Information&gt; 
       FIG. 33  is a block diagram showing storage internal mapping information  14000 . 
     The storage internal mapping information  14000  is, for example, a table which contains, for each storage level pool, a record of the following attribute values: a storage level pool identifier  14001 , storage level virtual volume identifiers  14002 , volume allocated capacity  14003 , and PDEV identifiers  14004 . 
     The storage level pool capacity  14001  is an identifier of the storage level pool. 
     The storage level virtual volume identifiers  14002  are identifiers of the storage level virtual volumes to which a portion of storage area is allocated from the storage level pool. 
     The volume identifiers  14003  are identifiers of volumes belonging to the storage level pool. 
     The PDEV identifiers  14004  are identifiers of the PDEVs  2100   a  which form the basis of the volumes belonging to the storage level pool. 
     Provided that the storage internal mapping information  14000  contains attribute values relating to mapping of the devices included in the storage system  2000 , a data structure other than a table may be employed, and attribute values relating to mapping information other than the attribute values described above may also be included. Furthermore, the storage internal mapping information  14000  may omit a portion of the attribute values described above, apart from the storage level pool identifier  14001 . 
     &lt;2-2. Description of Program Belonging to Storage System&gt; 
       FIG. 3  is a diagram showing the configuration of a storage control program  2500 . 
     As shown in  FIG. 28  as well, the storage control program  2500  comprises, for example, a storage virtualization module  2501 , a storage configuration management module  2502  and a command control module  2503 . A process for controlling the storage system  2000  is written in the storage control program  2500 , which is stored in the memory of the storage controller  2010  and executed. 
     The storage configuration management module  2502  manages the configuration of the storage areas of various types included in the storage system  2000 . In specific terms, the management of the configuration of the storage area means, for example, management of the volumes which make up the storage level pools, management of the PDEVs  2100   a  which make up the volumes, and so on. 
     The command control module  2503  interprets a command (for example, an I/O request) from a physical server  3000  or management server  1000 , and executes processing as stipulated by that command. 
     The storage virtualization module  2501  constructs volumes on the basis of PDEVs  2100   a . The storage virtualization module  2501  also constructs storage level virtual volumes. The storage virtualization module  2501  maps one or more volumes and one or more storage level virtual modules to a storage level pool. 
     3. Details of Physical Server 
       FIG. 29  is a diagram showing the details of information and programs stored in the memory  4050   b  of a physical server  3000 . 
     The memory  4050   b  stores server level pool information  15000 , server level virtual volume information  16000  and a server virtualization program  3200 . 
     The server level pool information  15000  is information relating to a server level pool. 
     The server level virtual volume information  16000  is information relating to server level virtual volumes. 
     The server virtualization program  3200  constructs virtual machines  3201 , a server level pool  3210 , server level virtual volumes  3220 , and the like, using the resources of a physical server  3000 . 
     &lt;3-1. Description of Information Belonging to Physical Server&gt; 
     &lt;3-1-1. Server Level Pool Information&gt; 
       FIG. 34  is a block diagram showing server level pool information  15000 . 
     The server level pool information  15000  includes, for example, for each server level pool, information relating to the server level pool, as well as information relating to the storage level virtual volumes belonging to the server level pool, and information relating to the server level virtual volumes to which storage area is allocated form the server level pool. More specifically, for example, the server level pool information  15000  is a table which contains, for each server level pool, a record of the following attribute values: a server level pool identifier  15001 , a server level pool capacity  15002 , a server level pool free capacity  15003 , server level virtual volume identifiers  15004 , a server level virtual volume total capacity  15005 , a configuration storage port number/LUN (Logical Unit Number)  15006 , an HA-SA size  15007  and an unallocated HL-SA identifier list  15008 . 
     The server level pool identifier  15001  is an identifier which has been allocated to the server level pool  3210  by the server virtualization module  3200 . 
     The server level pool capacity  15002  is the capacity of the server level pool  3210 . 
     The server level pool allocated capacity  15003  is the total capacity of the area, out of the server level pool capacity  15002 , which has been allocated to server level virtual volumes  3220 . 
     The server level virtual volume identifiers  15004  are identifiers of the server level virtual volumes to which a portion of storage area is allocated from the server level pool. 
     The server level virtual volume total capacity  15005  is the sum total of the capacities of all of the server level virtual volumes to which storage area is allocated from the server level pool. 
     The configuration storage port number/LUN  15006  is the LUN and port number for identifying a storage level virtual volume belonging to the server level pool (the LUN and port number are used in I/O requests as a parameter indicating a storage level virtual volume). The port number/LUN may be another identifier, provided that it enables a storage level virtual volume provided by the storage system  2000  to be specified. 
     The HL-SA size  15007  is a value indicating the management unit length (more specifically, the unit length which is allocated or released) of the area (HL-SA) of a volume included in the server level pool. 
     The unallocated LL-SA identifier list  15008  is a list of the identifiers of the areas (HL-SA) which are not allocated to a server level virtual volume that has been associated with the server level pool. 
     In the examples of identifiers shown in the drawings, an offset number from a list stored in the configuration storage port number/LUN  15006  is stated before the colon “:”, and an offset number from the start of the area (HL-SA) of the storage level virtual volume indicated by the configuration storage port number/LUN  15006  and the offset number is stated after the colon. The areas (HL-SA) are created by dividing up the volume from the start, by the HL-SA size  15007 , and offset numbers 0, 1, . . . , are allocated to the areas in order from the start of the volume. Taking as an example the identifier “00:002” of the unallocated HL-SA in the server level pool “SVPOOL- 1 ”, the “00” before the colon indicates the identifier of the storage level virtual volume at the start of the pool, and therefore the volume identifier corresponds to the storage level virtual volume having a “LUN of 0 at PORT Number XXX.XXX”, while the “002” after the colon indicates the third area (HL-SA) from the start of that storage level virtual volume. Incidentally, since the HL-SA size of the SVPOOL- 1  is 50 MB, then the third area (HL-SA) from the start will range from the 200 k block to the (300 k−1) block. 
     Provided that the server level pool information  15000  contains attribute values relating to a server level pool, a data structure other than a table may be employed, and attribute values relating to the server level pool configuration other than the attribute values described above may also be included. Furthermore, the server level pool information  15000  may omit a portion of the attribute values described above, apart from the server level pool identifier  15001 . 
     &lt;3-1-2. Server Level Virtual Volume Information&gt; 
       FIG. 35  is a block diagram showing server level virtual volume information  16000 . 
     The server level virtual volume information  16000  includes, for example, for each server level virtual volume, information relating to the server level virtual volume, as well as information relating to the server level pool which is the allocation source of the area allocated to the server level virtual volume, and information relating to virtual machine which uses the server level virtual volume. More specifically, for example, the server level virtual volume information  16000  contains, for each server level virtual volume, a record of the following attribute values: a server level virtual volume identifier  16001 , a server level virtual volume capacity  16002 , a server level virtual volume allocated capacity  16003 , a server level pool identifier  16004 , a server level pool capacity  16005 , a corresponding virtual machine identifier  16006 , a device identifier for virtual machine recognition  16007  and server level area conversion information  16008  (indicated as HL-area conversion information in the figure). 
     The server level virtual volume identifier  16001  is an identifier which has been allocated to the server level virtual volume by the server virtualization program  3200 . 
     The server level virtual volume capacity  16002  is the capacity of the server level virtual volume. 
     The server level virtual volume allocated capacity  16003  is the total capacity of the area (virtual area), out of the server level virtual volume capacity, to which storage area has been allocated from the server level pool. 
     The server level pool identifier  16004  is an identifier of the server level pool which is the allocation source of the area allocated to the server level virtual volume. 
     The server level pool capacity  16005  is the capacity of the server level pool which is the allocation source of the area allocated to the server level virtual volume. 
     The corresponding virtual machine identifier  16006  is the identifier of the virtual machine which uses the server level virtual volume. 
     The device identifier for virtual machine recognition  16007  is an identifier whereby the virtual machine  3201  recognizes the server level virtual volume (a device identifier which indicates the server level virtual volume). 
     The server level area conversion information  16008  is information that includes the identifiers of the areas (HL-SA) of the server level pool which have been allocated to each area (HL-AA) of the server level virtual volumes. An area (HL-AA) for which (HL-SA) is marked as “unallocated” means that an area (HL-SA) has not been allocated to the corresponding area (HL-AA). The server level area conversion information  16008  is created with all (or a portion) of the HL-AAs set to “unallocated” immediately after definition of the corresponding server level virtual volume, and as described below, the areas (HL-SA) are allocated in accordance with an initial write request which covers the range of a portion or all of the areas (HL-AA) and the write data of the write request is saved in the areas (HL-SA). 
     In the example illustrated, the storage level area conversion information  160008  is expressed in the form of a list, and identifiers which respectively indicate an area (HL-SA) allocated to an area (HL-AA) (or which indicate the value “unallocated”) are stored in sequence from the area (HL-AA) at the start of the server level virtual volume. 
     If the block address specifying the area (HL-AA) is the [Z] block address, then the address of the 512 byte block of the corresponding area (HL-SA) is determined as follows. 
     [HL-SA offset]=value obtained by dividing [Z] by [HL-SA size  15007  of corresponding server level pool] (rounded down to nearest integer). 
     [HL-SA offset internal address]=remainder obtained by dividing [Z] by [HL-SA size  15007  of corresponding server level pool] 
     [Storage level virtual volume where corresponding HL-SA resides]=value before colon [:] in identifier of [HL-SA offset] in list  16008   
     [Address in volume where corresponding LL-SA resides]=(value after [:] in [HL-SA offset] identifier in list  16008 )×[HL-SA size  15007  of corresponding storage level pool]+[HL-SA offset internal address]) 
     Therefore, when an I/O request specifying the 151K block address of the HDD- 1  (in other words, SVVVOL- 1 ) is received from the virtual machine  1 , the following calculation is carried out. 
     HL-SA offset=1. 
     HL-SA offset internal address=51 K block 
     Volume where corresponding HL-SA resides=01 (identified as LUN=2 at port number ZZZ. KKK by referring to the configuration storage port number/LUN  150006  in  FIG. 34 ) 
     Address in volume where corresponding HL-SA resides=851 K block 
     Provided that the server level virtual volume information  16000  contains attribute values relating to a server level virtual volume  3220 , a data structure other than a table may be employed, and attribute values relating to a server level virtual volume  3220  other than the attribute values described above may also be included. Furthermore, the server level pool information  16000  may omit a portion of the attribute values described above, apart from the server level virtual volume identifier  16001 . 
     &lt;3-2. Description of Program Belonging to Physical Server&gt; 
     The server virtualization program  3200  is now described. 
     The server virtualization program  3200  constructs virtual machines  3201 , a server level pool  3210 , server level virtual volumes  3220 , and the like, using the resources of a physical server  3000 . A more detailed description of the processing carried out by the server virtualization program  3200  is given in the section &lt;5-1. Thin provisioning in server&gt; below. 
     4. Details of Management Server 
       FIG. 2  is a diagram showing the details of information and programs stored in the memory  4050   c  of the management server  1000 . 
     The memory  4050   c  stores: storage level pool configuration information  1400 , storage level virtual volume configuration information  1500 , port/LUN correspondence information  1600 , server level pool configuration information  1700 , server level virtual volume configuration information  1800 , end-to-end capacity leverage ratio information  1900 , initial settings information  1910  and a management program  1200 . 
     The storage level pool configuration information  1400  is information relating to the configuration of storage level pools. Details of the storage level pool configuration information  1400  are given in &lt;4-1. Storage information&gt;. 
     The storage level virtual volume configuration information  1500  is information relating to the configuration of the storage level virtual volumes. Details of the storage level virtual volume configuration information  1500  are given in &lt;4-1. Storage information&gt;. 
     The port/LUN correspondence information  1600  is information relating to the port numbers and LUNs corresponding to the storage level virtual volumes which are provided by the storage system  2000  to the physical server  3000 . The port/LUN correspondence information  1600  is described in detail in &lt;4-1-3. Management server settings information&gt;. 
     The server level pool configuration information  1700  is information relating to the configuration of server level pools  3210 . Details of the server level pool configuration information  1700  are given in &lt;4-1-2. Physical server information&gt;. 
     The server level virtual volume configuration information  1800  is information relating to the configuration of the server level virtual volumes. Details of the storage level virtual volume configuration information  1800  are given in &lt;4-1-1. Server information&gt;. 
     The end-to-end capacity leverage ratio information  1900  is information relating to the end-to-end capacity leverage ratios of the storage level pools. The end-to-end capacity leverage ratio information  1900  is described in detail in &lt;4-1-3. Management server management information&gt;. 
     The initial settings information  1910  is information relating to the initial settings input by a storage administrator. The initial settings information  1910  is described in &lt;4-1-3. Management server management information&gt;. 
     The management program  1200  is a program which manages a storage system  2000  and physical servers  3000 . The management program  1200  contains a storage management module  1201 , a server management module  1202  and a leverage management module  1203 . 
     The storage management module  1201  is a module which manages a storage system  2000  by using the storage level pool configuration information  1400  and the storage level virtual volume configuration information  1500 . 
     The server management module  1202  is a module which manages a physical server  3000  by using the server level pool configuration information  1700  and the server level virtual volume configuration information  1800 . 
     The leverage management module  1203  is a module which manages the end-to-end capacity leverage ratio by using the port/LUN correspondence information  1600 , the end-to-end capacity leverage ratio information and the initial settings information  1910 . 
     The respective modules included in the storage control program  1200  do not necessarily have to be modules of a single program, and may respectively be separate program codes. 
     &lt;4-1. Information Managed by the Management Server&gt; 
     &lt;4-1-1. Storage Information&gt; 
     &lt;4-1-1a. Storage Level Pool Configuration Information&gt; 
       FIG. 6  is a block diagram showing storage level pool configuration information  1400 . 
     The storage level pool configuration information  1400  contains, for each storage level pool, information relating to the storage level pool and information relating to storage level virtual volumes corresponding to that storage level pool. More specifically, for example, the storage level pool configuration information  1400  is a table which contains, for each storage level pool, a record of the following attribute values: a storage level pool identifier  1401 , a storage level pool capacity  1402 , a storage level pool allocated capacity  1403 , corresponding storage virtual volume identifiers  1404 , a corresponding storage level virtual volume total capacity  1405 , pool configuration volume identifiers  1406 , and a storage apparatus identifier  1407 . 
     The storage level pool capacity  1401  is an identifier of the storage level pool. 
     The storage level pool capacity  1402  is the capacity of the storage level pool. 
     The storage level pool allocated capacity  1403  is the total capacity of the area, out of the storage level pool capacity, which has been allocated to the storage level virtual volume. 
     The corresponding storage level virtual volume identifier  1404  is the identifier of a storage level virtual volume which corresponds to the storage level pool. 
     The corresponding storage level virtual volume total capacity  1405  is the sum value of the capacities of all of the storage level virtual volumes corresponding to the storage level pool. 
     The pool configuration volume identifiers  1406  are identifiers of volumes belonging to the storage level pool. 
     The storage apparatus identifier  1407  is an identifier of the storage apparatus containing the volumes belonging to the storage level pool. 
     Provided that the storage level pool information  1400  contains attribute values relating to the composition of the storage level pool  2220 , a data structure other than a table may be employed, and attribute values relating to the configuration of a storage level pool  2220  other than the attribute values described above may also be included. Furthermore, the storage level pool information  1400  may omit a portion of the attribute values described above, apart from the storage level pool identifier  1401 . 
     The information elements  1401  to  1406  described above are obtained, for example, from the information elements  11001  to  11006  in the storage level pool information  11000  (see  FIG. 30 ) which is gathered by the management server  1000  from the storage apparatuses which make up the storage system. Furthermore, the information element  1407  is an information element which indicates which storage apparatus the storage level pool information  11000  has been gathered from. 
     &lt;4-1-1b. Storage Level Virtual Volume Configuration Information&gt; 
       FIG. 7  is a block diagram showing storage level virtual volume configuration information  1500 . 
     The storage level virtual volume configuration information  1500  includes, for each storage level virtual volume, information relating to the storage level virtual volume, and information relating to the storage level pool corresponding to that storage level virtual volume. More specifically, for example, the storage level virtual volume configuration information  1500  is a table which contains, for each storage level virtual volume, a record of the following attribute values: a storage level virtual volume identifier  1501 , a storage level virtual volume capacity  1502 , a storage level virtual volume allocated capacity  1503 , and a corresponding storage level pool identifier  1504 . 
     The storage level virtual volume identifier  1501  is an identifier of the storage level virtual volume. 
     The storage level virtual volume capacity  1502  is the capacity of the storage level virtual volume. 
     The storage level virtual volume allocated capacity  1503  is the total capacity of the area, out of the storage level virtual volume capacity, which has been allocated to the storage level virtual volume from the storage level pool. 
     The corresponding storage level pool identifier  1504  is an identifier of the storage level pool corresponding to the storage level virtual volume. 
     Provided that the storage level virtual volume configuration information  1500  contains attribute values relating to a storage level virtual volume  2230 , a data structure other than a table may be employed, and attribute values for a storage level virtual volume  2230  other than the attribute values described above may also be included. Furthermore, the storage level virtual volume  2230  information may omit a portion of the attribute values described above, apart from the storage level virtual volume identifier  1501 . 
     The information elements  1501  to  1504  described above are obtained, for example, from the information elements  12001  to  12004  in the storage level pool information  11000  (see  FIG. 31 ) which is gathered by the management server  1000  from the storage apparatuses which make up the storage system. 
     &lt;4-1-2. Physical Server Information&gt; 
     &lt;4-1-2a. Server Level Pool Configuration Information&gt; 
       FIG. 9  is a block diagram showing server level pool configuration information  1700 . 
     The server level pool configuration information  1700  contains, for each server level pool, information relating to the server level pool and information relating to server level virtual volumes corresponding to that server level pool. More specifically, for example, the server level pool information  1700  is a table which contains, for each server level pool, a record of the following attribute values: a server level pool identifier  1701 , a server level pool capacity  1702 , a server allocated capacity  1703 , corresponding server level virtual volumes  3220 , a corresponding server level virtual volume total capacity  1705 , volume source storage apparatuses, and a configuration storage port number/LUN  1707 . 
     The server level pool capacity  1701  is an identifier of the server level pool. 
     The server level pool capacity  1702  is the capacity of the server level pool. 
     The server level pool allocated capacity  1703  is the total capacity of the area, out of the server level pool capacity, which has been allocated to the server level virtual volumes. 
     The corresponding server level virtual volume identifiers  1704  are identifiers of server level virtual volumes which correspond to the storage level pool. 
     The corresponding server level virtual volume total capacity  1705  is the sum value of the capacities of all of the server level virtual volumes corresponding to the server level pool. 
     The volume source storage apparatus identifiers  1407  are identifiers of the storage apparatuses which provide the storage level virtual volumes corresponding to the server level pool, to the physical server  3000 . 
     The configuration storage volume port number/LUN  1707  is a port number which allows the physical server  3000  to access a storage level virtual volume corresponding to the server level pool and a LUN whereby the physical server  3000  can recognize the storage level virtual volume by SCSI. 
     Provided that the server level pool configuration information  1700  contains attribute values relating to a server level pool  3210 , a data structure other than a table may be employed, and attribute values relating to the server level pool  3210  other than the attribute values described above may also be included. Furthermore, the server level pool configuration information  1700  may omit a portion of the attribute values described above, apart from the server level pool identifier  1701 . 
     The information elements  1701  to  1706  described above are obtained, for example, from the information elements  15001  to  15006  in the server level pool information  15000  (see  FIG. 34 ) which is gathered by the management server  1000  from the physical servers. Furthermore, the information element  1507  is an information element that indicates which physical server the server level pool information  15000  has been gathered from. 
     &lt;4-1-2b. Server Level Virtual Volume Configuration Information&gt; 
       FIG. 10  is a block diagram showing server level virtual volume configuration information  1800 . 
     The server level virtual volume configuration information  1800  includes, for each server level virtual volume, information relating to the server level virtual volume, and information relating to the server level pool corresponding to that server level virtual volume. More specifically, for example, the server level virtual volume information  1800  is a table which contains, for each server level virtual volume, a record of the following attribute values: a server level virtual volume identifier  1801 , a server level virtual volume capacity  1802 , a server level virtual volume allocated capacity  1803 , a server level virtual volume unallocated capacity  1804 , a server level virtual volume used capacity  1805 , a corresponding server level pool identifier  1806 , a corresponding virtual machine identifier  1807  and a device identifier for virtual machine recognition  1808 . 
     The server level virtual volume identifier  1801  is an identifier of the server level virtual volume. 
     The server level virtual volume capacity  1802  is the capacity of the server level virtual volume. 
     The server level virtual volume allocated capacity  1803  is the total capacity of the area, out of the server level virtual volume capacity, which has been allocated to the server level virtual volume from the storage level pool. 
     The server level virtual volume unallocated capacity  1804  is the total capacity of the area (virtual area), out of the server level virtual volume capacity, to which storage area has not been allocated from the server level pool. 
     The server level virtual volume used capacity  1805  is the capacity to which data has been written by a virtual machine, out of the server level virtual volume capacity. 
     The corresponding server level pool identifier  1806  is an identifier of the server level pool corresponding to the server level virtual volume. 
     The corresponding virtual machine identifier  1807  is the identifier of the virtual machine which is the allocation destination of the server level virtual volume. 
     The device identifier for virtual machine recognition  1808  is an identifier whereby a virtual machine recognizes a server level virtual volume as a device (for example, as a hard disk drive). 
     Provided that the server level virtual volume configuration information  1800  contains attribute values relating to a server level virtual volume  3220 , a data structure other than a table may be employed, and attribute values for a server level virtual volume  3220  other than the attribute values described above may also be included. Furthermore, the server level virtual volume  3220  information may omit a portion of the attribute values described above, apart from the server level virtual volume identifier  1801 . 
     The information elements  1801  to  1804  and  1806  to  1808  described above are obtained, for example, from the information elements  16001  to  16001  in the server level virtual volume information  16000  (see  FIG. 35 ) which is gathered by the management server  1000  from the physical servers. Furthermore, the information element  1805  is an information element which is determined by calculating the data volume written to the server level virtual volume by the virtual machine. 
     &lt;4-1-3. Management Server Management Information&gt; 
     &lt;4-1-3a. Port-LUN Correspondence Information&gt; 
       FIG. 8  is a block diagram showing port/LUN correspondence information  1600 . 
     The port/LUN correspondence information  1600  is, for example, a table which contains, for each storage level virtual volume, a record of the attribute values: port # (port number)  1602 , LUN  1603  and internal volume ID  1601 . 
     The port # 1602  is the port number used by a physical server  3000  to access a provided storage level virtual volume  2230 , when the storage system  2000  has provided a storage level virtual volume  2230  to the physical server  3000 . 
     The LUN  1603  is an identification number which allows the physical server  3000  to recognize by SCSI a storage level virtual volume  2230  provided by the storage system  2000 . 
     The internal volume ID  1601  is an identifier for identifying a storage level virtual volume  2230  provided to a physical server  3000  by the storage system  2000 . 
     Provided that the port/LUN correspondence information  1600  includes attribute values relating to the correspondences between the port number  1602 , the LUN  1603  and the internal volume ID  1601 , a data structure other than a table may be employed and attribute values for the correspondence between the port number  1602 , LUN  1603  and internal volume ID  1601  other than the attribute values described above may also be included. Furthermore, the port/LUN correspondence information  1600  may omit a portion of the attribute values described above, apart from the internal volume ID  1601 . 
     The information elements  1601  to  1603  described above can be created in the following way, for example. The correspondence information  1600  shown in  FIG. 8  is constructed using the storage level virtual volume identifiers, port numbers and LUNs in the storage level virtual volume information  12000  (see  FIG. 31 ) gathered from the storage apparatuses by the management server. 
     &lt;4-1-3b. End-to-End Capacity Leverage Ratio Information&gt; 
       FIG. 11  is a block diagram showing the end-to-end capacity leverage ratio information  1900 . 
     The end-to-end capacity leverage ratio information  1900  is, for example, a table which contains, for each storage level pool, a storage level pool identifier  1901  and an end-to-end capacity leverage ratio  1902 . 
     The storage level pool capacity  1901  is an identifier of the storage level pool. 
     The end-to-end capacity leverage ratio  1902  is the end-to-end capacity leverage ratio corresponding to the storage level pool (100×(total capacity of all server level virtual volumes corresponding to storage level pool)/(capacity of storage level pool)) (%). 
     Provided that the end-to-end capacity leverage ratio information  1900  includes attribute values relating to the capacity leverage ratio of the pool unit, a data structure other than a table may be employed and attribute values relating to the capacity leverage ratio of the pool unit other than the attribute values described above may also be included. Furthermore, the end-to-end capacity leverage ratio  1900  may omit a portion of the attribute values described above, apart from the storage level pool identifier  1901 . 
     &lt;4-1-3c. Initial Settings Information&gt; 
       FIG. 12  is a block diagram showing initial settings information  1910 . 
     The initial settings information  1910  is a table containing one or more records including the attribute values of end-to-end capacity leverage ratio threshold value  1911  and information gathering interval  1912 , for example. 
     The end-to-end capacity leverage ratio threshold value  1911  is a threshold value indicating the upper tolerance limit of the capacity leverage ratio relating to the storage level pool  2220 , which is input by the storage administrator via a setup screen of the management program  1200 . 
     The information gathering interval  1912  is the interval between the timings at which the end-to-end capacity leverage ratio  1902  is calculated, as input by the storage administrator via the setup screen of the management program  1200 . 
     Provided that the initial settings information  1910  contains attribute values relating to the initial settings input by the storage administrator, a data structure other than a table may be employed, and attribute values relating to the initial settings other than the attribute values described above may also be included. Furthermore, the initial settings information  1910  may omit a portion of the attribute values described above, apart from the information gathering interval  1912 . 
       FIG. 13  shows a display screen of the end-to-end capacity leverage ratio. 
     The leverage ratio display screen  1403  is a screen which is displayed by the management program  1200 . The reason why, for example, the end-to-end capacity leverage ratio of the storage level pool “STPOOL- 1 ” is 500% is as follows. 
     From the information  1400  in  FIG. 6 , the capacity “10000 MB” of the storage level pool corresponding to the identifier “STPOOL- 1 ” is specified. Furthermore, the corresponding storage level virtual volume identifiers “STVVOL- 1 ” and “STVVOL- 2 ” which correspond to the identifier “STPOOL- 1 ” are also specified. 
     The port number and LUN corresponding respectively to the identifiers “STVVOL- 1 ” and “STVVOL- 2 ” are specified from the information  1600  in  FIG. 8 . 
     Using these port numbers and LUNs, the server level pool identifier “SVPOOL- 1 ” is specified from the information in  FIG. 9 . 
     Using this identifier “SVPOOL- 1 ”, the server level virtual volume capacities “30000 MB” and “20000 MB”, in other words, a total capacity of “50000 MB”, are specified from the information  1800  in  FIG. 10 . 
     As a result of the foregoing, a total capacity of “50000 MB” in the server level virtual volumes which correspond to the storage level pool is identified in respect of the capacity “10000 MB” of the storage level pool “STPOOL- 1 ”, and consequently, an end-to-end capacity leverage ratio of 100×50000/10000=500%, is calculated. 
     The display format and display information shown in  FIG. 13  are one example and other information apart from that shown in  FIG. 13  may be displayed, provided that it relates to the end-to-end capacity leverage ratio. Furthermore, the GUI may also employ a different format. 
     5. Thin Provisioning 
     &lt;5-1. Thin Provisioning in Storage System&gt; 
       FIG. 4  is a diagram illustrating thin provisioning carried out in a storage system  2000 . 
     In the storage system  2000 , volumes  2210 , a storage level pool  2220  and storage level virtual volumes  2230  are constructed by a storage virtualization module  2501  of the storage control program  2500 . 
     The volumes  2210  are constructed by the storage virtualization module  2501  grouping together the storage area of one or more PDEVs  2100   a . The storage areas of the volumes  2210  are distributed and mapped to the storage area of one or more PDEVs  2100   a  which make up a volume  2210 , under control implemented by the storage controller  4050 . 
     The storage level pool  2220  is constructed by the storage virtualization module  2501 . The storage area of the storage level pool  2220  is distributed and mapped to the storage area of one or more volumes  2210  which correspond to the storage level pool  2220 , under control implemented by the storage controller  4050 . 
     The storage level virtual volumes  2230  are constructed by the storage virtualization module  2501 . The storage level virtual volumes  2230  have a virtual area (LL-AA). In contrast to the areas (LL-SA) of the volumes  2210 , immediately after the definition of the storage level virtual volumes  2230 , the areas (LL-AA) of the storage level virtual volume  2230  are not associated with the physical storage region of a PDEV  2100   a.    
     When a write request to a virtual area (LL-AA) of a storage level virtual volume  2230  has been issued, if a portion of the area (LL-SA) inside the pool  2220  has not been allocated to that area (LL-AA), then under the control of the storage controller  4050   a , the unallocated area (LL-SA) of the storage level pool  2220  is mapped dynamically. 
     The whole of the virtual storage area of the storage level virtual volumes  2230  does not have to correspond to a physical storage area, such as a storage area of a PDEV  2100   a , and therefore it is possible to set the virtual storage area (capacity) of the storage level virtual volumes  2230  to a value that is higher than the physical storage area of the storage system  2000  (for example, the capacity of the pool  2220 ). Furthermore, if the unallocated area (LL-SA) is insufficient immediately after starting access to the storage level virtual volume, then it is possible to prevent failure of the write request due to the insufficient unallocated area (LL-SA), by incorporating a new volume into the pool  2220 , without changing the settings of the computer which is accessing the storage level virtual volume. 
     The storage system  2000  provides the storage level virtual volumes  2230  to the physical server  3000 . The physical storage area of the PDEV  4050   a  is accessed by the physical server  3000  via the storage level virtual volumes  2230  and the volumes  2210  which form the storage level pool  2220 . 
     &lt;5-1-1. Addition of Volume to Storage Level Pool&gt; 
       FIG. 26  is a flow diagram showing processing for adding a volume  2210  to the storage level pool  2220 . 
     The setup of the storage level pool  2220  is implemented by the storage virtualization module  2501 . 
     (Step S 1101 ) Firstly, the storage administrator inputs information about the volumes  2210  to be set in the storage level pool  2220 , to the management program  1200 . The identifier of the storage level pool  2220 , the threshold value, the number of volumes  2210  and the volume identifiers are established. 
     (Step S 1102 ) The storage management module  1201  generates a command instructing set-up of the storage level pool  2220  including the input information, and sends this command to the storage system  2000  via the NIC. 
     (Step S 1103 ) In the storage system  2000 , the command sent from the physical server  1000  is received by the command control module  2503 , via the NIC. 
     The command control module  2503  recognizes the contents of the received command. If the contents of the command are invalid, then the module  2503  rejects the command (and returns an error, for example). 
     (Step S 1104 ) If the command instructs the setting up of a storage level pool  2220 , then the command control module  2503  passes on the received command to the storage virtualization module  2501 . The storage virtualization module  2501  receives the command and starts storage level pool setup processing. 
     (Step S 1105 ) The storage virtualization module  2501  firstly examines the storage level pool information  11000  and confirms that the storage level pool identifier  11001  relating to the command is valid. Furthermore, the storage virtualization module  2501  confirms whether the storage level pool identifier  11001  has not yet been defined. 
     (Step S 1106 ) Thereupon, the storage virtualization module  2501  confirms whether or not the volume  2210  relating to the command is usable. More specifically, if the volume  2210  relating to the command is being formatted, for example, then that volume  2210  cannot be used and therefore the storage virtualization module  2501  rejects the command (by returning an error, for example). Furthermore, if the volume  2210  relating to the command is already in use (for example, if the path to the volume  2210  has been defined, if the volume is in use by a copy function, or the like, or if the volume has been reserved as a copy destination), then the storage virtualization module  2501  rejects the command since the volume  2210  is not usable. 
     (Step S 1107 ) Thereupon, the storage virtualization module  2501  sets the storage level pool capacity  11002  and the volume identifier  11004  in the storage level pool information  11000 . By means of this processing carried out by the storage virtualization module  2501 , a volume  2210  is added to the storage level pool  2220 . The storage virtualization module  2501  adds all or a portion of the area of the registered volume to the unallocated LL-SA identifier list  11008 , as an LL-SA. 
     (Step S 1108 ) Next, the storage control program  2500  sends a reply indicating that the command was successful, to the management server  1000 . 
     Upon receiving a reply from the storage system  2000 , the storage configuration management module  2502  of the management server  1000  ends processing. 
     By means of the processing described above, a volume  2210  is added to the storage level pool  2220 . 
     &lt;5-1-2. Reading from Storage Level Virtual Volume&gt; 
       FIG. 24  is a flow diagram of processing for reading data from a storage level virtual volume. 
     The physical server sends an I/O request by specifying the LUN of a storage level virtual volume and the block address in the volume. This I/O request is a data read request. 
     (Step S 901 ) In the storage system  2000 , the command control module  2503  receives an I/O request from the physical server  3000 . If the content of the received I/O request is invalid, then this request is rejected (an error is returned, for example). If the content of the received I/O request is valid, then the command control module  2503  analyzes the content of the I/O request. As a result of this analysis, the command control module  2503  identifies that the I/O request is a data read request. 
     (Step S 902 ) Next, the command control module  2503  acquires the block address of the storage level virtual volume  2230  relating to the received request, which is to be read from. 
     (Step S 903 ) Thereupon, the command control module  2503  acquires the block address of the area (LL-SA) of the volume that has been mapped to the area (LL-AA) including the address of the area in the read request, from the storage level pool  2220  corresponding to the storage level virtual volume  2230  that is to be read. In this case, the address of the area of the storage level virtual volume  2230  in the read request may have been distributed and mapped to the addresses of a plurality of volumes  2210 . This processing is carried out by referencing the storage level pool information  11000  and the storage level virtual volume information  12000 , but the details of this processing have already been described in explaining the respective information. 
     (Step S 904 ) Thereupon, the command control module  2503  refers to the volume information  14000 , identifies the PDEV  2100   a  corresponding to the address of the area of the volume  2210 , and acquires the address of that PDEV  2100   a.    
     (Step S 905 ) Thereupon, the command control module  2503  reads out data relating to the request from the address of the PDEV  2100   a  and sends this data to the physical server  3000 . 
     (Step S 906 ) The command control module  2503  then sends a read request completion report to the physical server  3000  and ends processing. 
     If, at step S 903 , there is no volume area (LL-SA) allocated to the area (LL-AA) including the address of the region in the read request, then a clear value (for example, a string of zeros) can be sent to the physical server  3000 . 
     &lt;5-1-3. Writing to Storage Level Virtual Volume&gt; 
       FIG. 25  is a portion of a flow diagram showing a process of writing data to a storage level virtual volume  2230 , and  FIG. 39  is the continuation of this flow diagram. 
     The physical server  3000  sends an I/O request by specifying the LUN of a storage level virtual volume  2230  and the block address in the volume. This I/O request is a data write request. 
     (Step S 1001 ) In the storage system  2000 , the command control module  2503  receives an I/O request from the physical server  3000 . If the received I/O request is invalid, then this request is rejected (an error is returned, for example). The command control module  2503  then analyzes the content of this I/O request. As a result of this analysis, the command control module  2503  identifies that the I/O request is a data write request. 
     (Step S 1002 ) Next, the command control module  2503  acquires the block address of the storage level virtual volume  2230  relating to the received write request. 
     (Step S 1003 ) Thereupon, the command control module  2503  refers to the storage level virtual volume information  12000 , identifies the storage level pool  2220  corresponding to the storage level virtual volume  2230  and acquires the status of the pool. 
     (Step S 1004 ) The command control module  2503  refers to the storage level pool information  11000 , identifies the volume  2210  corresponding to the storage level pool  2220 , and judges whether or not the volume  2210  is usable. 
     (Step S 1005 ) If the volume  2210  is not usable, then access to the volume  2210  is not possible, and therefore the command control module  2503  sends an I/O error to the physical server  3000 . 
     (Step S 1006 ) If it is judged that the volume  2210  is usable, then the command control module  2503  sends a notification that the transfer of write data is possible, to the physical server  3000  which sent the request. The physical server  3000  receives this and sends write data to the storage system  2000 . 
     (Step S 1007 ) The command control module  2503  receives the write data sent by the physical server  3000 . 
     (Step S 1010 ) Firstly, the storage virtualization module  2501  refers to the storage level virtual volume information  12000  and the storage level pool information  11000  and checks whether an area (LL-SA) of the storage level pool  2220  has been allocated to the area (LL-AA) which includes the block address of the write request. 
     (Step S 1011 ) If it is judged at step S 1010  that an area has been allocated, then the storage virtualization module  2501  refers to the storage level virtual volume information  12000  and the storage level pool information  11000  and acquires the volume allocated to the area (LL-AA) which includes the specified block address, and the block address of the area (LL-SA) of that volume. 
     (Step S 1012 ) Thereupon, the storage virtualization module  2501  refers to the volume information  13000 , identifies the PDEV  2100   a  corresponding to the volume  1011  and the block address acquired at step S 1011 , acquires the address of the region of the PDEV  2100   a  and writes the write data (the data appended to the write request). 
     (Step S 1013 ) Upon completing the writing of the write data, the storage virtualization module  2501  reports the end of writing to the command control module  2503 . The command control module  2503  receives this report, sends a write request completion report to the physical server  3000  and ends processing. 
     (Step S 1014 ) On the other hand, if it is judged at step S 1010  that an area has not been allocated, then the storage virtualization module  2501  refers to the storage level pool information  11000  and confirms whether there is an unallocated area (LL-SA) in the corresponding storage level pool  2220 . This step can be achieved by referring to the unallocated LL-SA identifier list  11008 . 
     (Step S 1015 ) If it is judged at step S 1014  that there is an unallocated area (LL-SA), then the storage virtualization module  2501  selects the unallocated area (LL-SA) of the storage level pool  2220 , acquires the volume and block address of the selected area (LL-SA), and allocates same to the area (LL-AA) judged to be unallocated at step S 1010 . The process of selecting the area (LL-SA) in this step can be made, for example, by extracting an unallocated area (LL-SA) from the start of the unallocated LL-SA identifier list  11008 . Furthermore, in the method described in  FIG. 30  and  FIG. 31 , it is possible to specify the identifier and the block address of the volume of the selected area (LL-SA). 
     (Step S 1016 ) The module  2501  then updates the storage level pool information  11000  and the storage level virtual volume information  12000 . More specifically, the module  2501  increases the allocated capacity  11003  of the storage level pool and the allocated capacity  12003  of the storage level virtual volume by the capacity of the selected area (LL-SA). Furthermore, the value in the storage level area conversion information  12007  which corresponds to the area (LL-AA) from step S 1010  is changed from unallocated to the volume and block address just acquired. 
     (Step S 1017 ) On the other hand, if it is judged that there is no (or insufficient) unallocated area (LL-SA) at step S 1014 , then the storage virtualization module  2501  changes the status of the management information of the storage level pool  2220  to “pool capacity insufficient”. 
     (Step S 1018 ) The module  2501  then reports the pool capacity insufficiency to the physical server  3000  that issued the I/O request and the storage system  2000 . 
     By means of the processing described above, processing of a data write request by the physical server  3000  is completed. 
     &lt;5-1. Thin Provisioning in Server&gt; 
       FIG. 5  is a diagram illustrating thin provisioning carried out in a physical server  3000 . 
     In the physical server  3000 , a server level pool  3210 , server level virtual volumes  3220  and virtual machines  3201  are constructed by the server virtualization program  3200 . The server level pool  3210  is a pool which enables a storage region including a plurality of areas (LL-AA) of a plurality of storage level virtual volumes  2230  which are provided by the storage system  2000  to be used as an area (HL-SA). The server level pool  3210  is constructed from one or more storage level virtual volumes  2230  allocated from the storage system  2000  by the server virtualization program  3200 . The server level pool  3210  principally uses a file system format, and stores image files of the virtual machines  3201  and image files of the server level virtual volumes  3220 , and the like. Furthermore, when a virtual machine is temporarily halted, the data stored virtually in the memory of the virtual machine is also stored as an image file. In other words, from the perspective of the physical server, it appears as if the various data which has been stored in the image file, memory image and server level virtual volume  3220  relating to the virtual machine is stored in a storage level virtual volume. A management area for the server level virtual volumes  3220  is reserved inside the server level pool  3210 . This management area stores address information for the virtual storage areas of the server level virtual volumes  3220 , mapping information on mapping to the storage level virtual volumes  2230  provided by the storage system  2000 , and the like. 
     The server level virtual volumes  3220  are constructed by the server virtualization program  3200 . The server level virtual volumes  3220  each have a virtual storage area. In response to a write request from a virtual machine  3201 , the server virtualization program  3200  dynamically maps an area of the required capacity from the virtual storage area of a server level virtual volume  3220  to the storage area of the server level pool  3210 . 
     The virtual machines  3201  are virtual computers which are constructed by the server virtualization program  3200 . In the virtual server environment, a plurality of virtual machines  3201  operate by sharing the physical resources of a physical server. Similarly to a physical server, a virtual machine  3201  can be installed with an OS  3230 , and can be used as an independent server machine. The virtual machine  3201  accesses the storage area of the server level pool  3210  (actually the storage level virtual volume) via a server level virtual volume  3220 . 
     Access from a virtual machine  3201  to the server level virtual volume  3220  is controlled by the server virtualization program  3200 . By this means, the server level virtual volume  3220  is recognized in the same way as a storage device having a physical storage area, by the OS  3230  of the virtual machine  3201 . The control performed by the server virtualization program  3200  includes the processes of reading, writing and capacity inquiry, with respect to the server level virtual volumes  3220 , and these processes are described hereinafter. A capacity inquiry request issued by the OS  3230  running on the virtual machine  3201  is a request for acquiring the capacity of a server level virtual volume  3220  which is necessary when the OS  3230  is to use that volume. 
     In the description given below, SCSI is used as an example of the I/O protocol issued to the server level virtual volume  3220  by the OS  3230  executed on the virtual machine  3201 . However, as an alternative to a SCSI protocol, it is also possible to employ other block access type protocols, such as IDE or SAS, for example. 
     &lt;5-1-1. Setting Up Server Level Pool&gt; 
       FIG. 21  is a flow diagram showing the processes of setting up and adding a storage level virtual volume  2230  to the server level pool  3210 . 
     (Step S 1201 ) Firstly, the storage administrator inputs information about the volumes to be set in the server level pool  3210 , to the server virtualization program  3200 . Storage level virtual volumes provided from the storage system  2000  are used as the volumes set in the server level pool  3210 . The identifier and threshold value of the server level pool  3210 , and the number and LUN  1603  of the storage level virtual volumes  2230  are established. 
     (Step S 1202 ) The server virtualization program  3200  confirms whether or not the command instructing the setup of the server level pool  3210  and containing the input information is valid. If the command is invalid, then the program  3200  rejects the command (and returns an error, for example). 
     (Step S 1203 ) The server virtualization program  3200  firstly refers to the server level pool information  15000  and confirms that the server level pool identifier  1801  relating to the command is valid. 
     (Step S 1204 ) Thereupon, the server virtualization module  3200  confirms whether or not the storage level virtual volume  2230  relating to the command is usable. More specifically, if the storage level volume  2230  relating to the command is being formatted, for example, then that storage level virtual volume  2230  cannot be used and therefore the program  3200  rejects the command (by returning an error, for example). Furthermore, if the storage level virtual volume  2230  relating to the command is already in use (for example, if the path to the storage level virtual volume  2230  has been defined), then that storage level virtual volume  2230  is not usable and the program  3200  rejects the command. 
     (Step S 1205 ) Next, the server virtualization program  3200  sets the server level pool capacity  15002  and the configuration storage port number/LUN  15006  in the server level pool information  15000 . By means of this processing performed by the server virtualization program  3200 , a storage level virtual volume  2230  is set in the server level pool  3210 . The server virtualization program  3200  then adds all or a portion of the areas of the registered storage level virtual volume to the unallocated HL-SA identifier list  15008 , as an HL-SA. 
     &lt;5-1-2. I/O to Server Level Virtual Volume&gt; 
     &lt;5-1-2a. Processing of Capacity Inquiry Request in Relation to Server Level Virtual Volume&gt; 
     This process is described with respect to a case where the OS  3230  running on the virtual machine  3201  has issued a capacity inquiry request. Normally, the OS  3230  subsequently issues a write request or read request, and executes file system format processing for the server level virtual volumes  3220 . 
     The OS  3230  on the virtual machine  3201  specifies a device identifier for virtual machine recognition  1808  and issues a capacity inquiry request. In response to this request, the server virtualization program  3200  returns the capacity of the server level virtual volume  3220  to the OS  3230  on the virtual machine  3201 , by carrying out the processing described below. By this means, the OS  3230  on the virtual machine  3201  is able to ascertain the capacity of the server level virtual volume  3220 . 
     (Step A) The server virtualization program  3200  receives a capacity inquiry request sent by the OS of the virtual machine  3201 . 
     (Step B) The server virtualization program  3200  analyzes the content of the request. The program then refers to the server level virtual volume information  16000  and specifies the server level virtual volume identifier  16001  corresponding to the device identifier for virtual machine recognition  16007  which is the destination of the inquiry. 
     (Step C) The server virtualization program  3200  acquires the server level virtual volume capacity  16002  of the identifier specified at step B, from the server level virtual volume information  16000 . 
     (Step D) The server virtualization program  3200  reports the capacity acquired at step C to the OS  3230  on the virtual machine  3201 , as the disk size of the storage device recognized by the OS  3230  on the virtual machine  3201 , and then terminates processing. 
     By means of the processing described above, the OS  3230  on the virtual machine  3201  is able to ascertain the capacity of the server level virtual volume  3220 . 
     &lt;5-1-2b. Processing of Read Request to Server Level Virtual Volume&gt; 
       FIG. 22  is a flow diagram of processing carried out when the server virtualization program has received a read request from a virtual machine to a server level virtual volume. 
     This process is started when the server virtualization program  3200  detects the issue of a read request in which the OS  3230  on the virtual machine  3201  specifies the device identifier for virtual machine recognition of the server level virtual volume  3220  that is to be read from, and a block address and block length. 
     (Step S 1301 ) The server virtualization program  3200  receives an I/O request from the virtual machine  3201 . If the content of the received I/O request is invalid, then the program  3200  rejects the request (by returning an error, for example). If the content of the received I/O request is valid, then the program  3200  analyzes the content of the I/O request. As a result of this analysis, the server virtualization program  3200  identifies that the I/O request is a data read request. 
     (Step S 1302 ) Next, the server virtualization program  3200  acquires the server level virtual volume  3220  relating to the received request, which is to be read from, and the block address in the object server level virtual volume. 
     (Step S 1303 ) Next, the server virtualization program  3200  refers to the server level virtual volume information  16000 , and acquires the identifier of the storage level virtual volume  2230  which has been mapped to the area (HL-AA) that includes the address of the region in the read request, and the address of the area (HL-SA) of the storage level virtual volume, from the server level pool  3210  corresponding to the server level virtual volume  3220  that is to be read from. In this case, the address of the region in the read request to the storage level virtual volume  3220  may have been distributed and mapped to the addresses of a plurality of storage level virtual volumes  2230 . This processing is carried out by referring to the server level pool information  15000  and the server level virtual volume information  16000 , but the details of this processing have already been described in explaining the respective information. 
     (Step S 1304 ) Next, the server virtualization program  3200  sends the identifier of the storage level virtual volume  2230  acquired at step S 1303  and a read request which specifies the address of the corresponding area (HL-SA) of the area (HL-SA) storage level virtual volume  2230 , to the storage system  2000 . Data relating to the read request is received from the server virtualization program  3200  and the data is sent to the virtual machine  3201 . 
     (Step S 1305 ) A read request completion report is then notified to the virtual machine  3201  and processing is terminated. 
     If, at step S 1303 , there is no volume area (HL-SA) allocated to the area (HL-AA) including the address of the region in the read request, then a clear value (for example, a string of zeros) can be sent to the virtual machine  3201 . 
     &lt;5-1-2c. Processing of Write Request to Server Level Virtual Volume&gt; 
       FIG. 23  and  FIG. 40  are flow diagrams of processing carried out when the server virtualization program has received a write request from a virtual machine to a server level virtual volume. 
     This process is started when the server virtualization program  3200  detects the issuing of a write request in which the OS  3230  on the virtual machine  3201  specifies the device identifier for virtual machine recognition of the server level virtual volume  3220  that is to be written to, and a block address and block length. 
     (Step S 1401 ) In the physical server  3000 , the server virtualization program  3200  receives an I/O request from the virtual machine  3201 . If the received I/O request is invalid, the program  3200  rejects that I/O request. If the received I/O request is valid, then the program  3200  analyzes the content of the I/O request. As a result of this analysis, the server virtualization program  3200  identifies that the I/O request is a data write request. 
     (Step S 1402 ) Thereupon, the server virtualization program  3200  acquires the identifier of the server level virtual volume  3220  relating to the received write request, and the block address in that server level virtual volume. 
     (Step S 1403 ) Next, the server virtualization program  3200  refers to the server level virtual volume information  16000 , identifies the server level pool  3210  corresponding to the server level virtual volume  2230  and acquires the status thereof. 
     (Step S 1404 ) The server virtualization program  3200  refers to the server level pool information  15000 , identifies the storage level virtual volume  2230  corresponding to the server level pool  3210 , and judges whether or not that storage level virtual volume  2230  is usable. 
     (Step S 1405 ) If the storage level virtual volume  2230  is not usable, then that storage level virtual volume  2230  cannot be accessed and therefore the server virtualization program  3200  reports an I/O error to the virtual machine which sent the request. 
     (Step S 1406 ) If it is judged that the storage level virtual volume  2230  is usable, then the server virtualization program  3200  sends a notification that the transfer of write data is possible, to the virtual machine which sent the request. Upon receiving this notification, the virtual machine sends write data to the server virtualization program  3200 . 
     (Step S 1407 ) The server virtualization program  3200  receives write data sent by the physical server  3000 . 
     (Step S 1410 ) Firstly, the server virtualization program  3200  refers to the server level virtual volume information  16000  and the storage level pool information  15000  and checks whether an area (HL-SA) of the server level pool  3210  has been allocated to the area (HL-AA) which includes the block address of the write request. [0h] 
     (Step S 1411 ) If it is judged at step S 1410  that an area has been allocated, then the server virtualization program  3200  refers to the server level virtual volume information  16000  and the server level pool information  15000  and acquires the identifier (for example, the port number and LUN) of the storage level virtual volume allocated to the area (HL-AA) which includes the specified block address, and the block address of the area (HL-SA) of that volume. 
     (Step S 1412 ) Thereupon, the server virtualization program  3200  sends the write data together with the identifier of the storage level virtual volume acquired at step S 1411  and a write request specifying the block address of the storage level virtual volume. 
     (Step S 1413 ) Upon receiving the writing completion report of the write data from the storage system  2000 , the server virtualization program  3200  sends a write request completion report to the virtual machine that issued the request and then ends processing. 
     (Step S 1414 ) On the other hand, if it is judged at step S 1410  that an area has not been allocated, then the server virtualization program  3200  refers to the server level pool information  15000  and confirms whether there is an unallocated area (HL-SA) in the corresponding server level pool  3210 . This step can be achieved by referring to the unallocated HL-SA identifier list  15008 . 
     (Step S 1415 ) If it is judged at step S 1414  that there is an unallocated area (HL-SA), then the server virtualization program  3200  selects the unallocated area (HL-SA) of the storage level pool  2220 , acquires the volume and block address of the selected area (HL-SA), and allocates same to the area (HL-AA) judged to be unallocated at step S 1410 . The process of selecting the area (HL-SA) in this step can be made, for example, by extracting an unallocated area (HL-SA) from the top of the unallocated HL-SA identifier list  15008 . Furthermore, in the method described in  FIG. 34  and  FIG. 35 , it is possible to specify the identifier and the block address of the volume of the selected area (HL-SA). 
     (Step S 1416 ) The sever virtualization program  3200  then updates the server level pool information  15000  and the server level virtual volume information  16000 . More specifically, the program  3200  increases the allocated capacity  15003  of the server level pool and the allocated capacity  16003  of the server level virtual volume by the capacity of the selected area (HL-SA). Furthermore, the value in the server level area conversion information  16007  which corresponds to the area (HL-AA) from step S 1410  is changed from unallocated to the volume and block address just acquired. 
     (Step S 1417 ) On the other hand, if it is judged that there is no (or insufficient) unallocated area (HL-SA) at step S 1414 , then the server virtualization program  3200  changes the status of the management information of the server level pool  3210  to “pool capacity insufficient”. 
     (Step S 1418 ) The server virtualization program  3200  then reports the pool capacity insufficiency to the virtual machine that issued the I/O request and the physical sever  3000 . 
     By means of the processing described above, processing of a data write request by the physical server  3000  is completed. 
     If failure of the write request is reported by the storage system  2000  at step S 1412 , then a write failure report is returned to the virtual machine that issued the I/O request. 
     6. Processing Steps in First Embodiment 
     If too large a virtual volume capacity is set in respect of a limited physical storage capacity (for instance, the capacity of a storage level pool), then it is difficult to predict the rate of consumption of the physical storage capacity and the possibility of depletion of the physical storage capacity increases. Therefore, it is necessary to keep the ratio of the virtual volume capacity with respect to the physical storage capacity (the leverage ratio) at or below a set level. 
     In the processing according to a first embodiment, the storage administrator sets a threshold value for the end-to-end capacity leverage ratio, in the management server  1000 . If the end-to-end capacity leverage ratio exceeds the threshold value, the management server  1000  detects this and indicates that the end-to-end capacity leverage ratio has exceeded the threshold value. By this means, the storage administrator is able to identify sharp rise in the end-to-end capacity leverage ratio. 
     The processing carried out by the management program in the first embodiment is now described with reference to  FIG. 14  and  FIG. 15 . 
     &lt;6-1. Processing for Calculating and Displaying End-to-End Capacity Leverage Ratio as Performed by Management Program&gt; 
       FIG. 14  is a flow diagram of processing carried out by the management program  1200 . The details of the individual steps are described below. 
     (Step S 101 ) The management program  1200  receives initial settings information  1910  which has been input by the storage administrator via the setup screen of the management program  1200 . The threshold value of the capacity leverage ratio and the interval for gathering capacity information are included in the initial settings information  1910 . The threshold value of the capacity leverage ratio is a value which indicates the tolerable upper limit of the virtual volume capacity corresponding to the physical storage capacity, and the storage administrator sets this threshold value on the basis of a capacity schedule. Furthermore, the interval between gathering capacity information is the interval between the times at which the management program  1200  carries out the processing described below. Moreover, the storage management module  1201  receives information specifying the storage level pool  2220  from the storage administrator, and on the basis of this information, determines the storage level pool identifier  1401  for which the end-to-end capacity leverage ratio is to be calculated. The management program  1200  then stores the input threshold value for the capacity leverage ratio as the end-to-end capacity leverage ratio threshold value  1911  in the initial settings information  1910 , and stores the interval for gathering capacity information as the information gathering interval  1912  in same. Furthermore, the storage management module  1201  stores an identifier of the storage level pool determined as the object of end-to-end capacity leverage ratio calculation as the storage level pool identifier  1901  in the end-to-end capacity leverage ratio information  1900 . 
     (Step S 102 ) The management program  1200  gathers the capacity information for the storage system  2000  and the capacity information for the physical server  3000 , after the information gathering interval  1912  set by the storage administrator has elapsed, in other words, when the time for gathering capacity information arrives. More specifically, for example, the storage management module  1201  of the management program  1200  acquires the capacity information of the storage system  2000  from the storage system  2000 , and the server management module  1202  of the management program  1200  gathers capacity information for the physical server  3000 . The specific method of gathering capacity information is described below. 
     (Step S 103 ) A leverage management module  1203  of the management program  1200  carries out processing for calculating the end-to-end capacity leverage ratio on the basis of the acquired capacity information of the physical server  3000  and the capacity information of the storage level pool  2220  specified by the storage administrator. The details of the processing of the end-to-end capacity leverage ratio are described later with reference to  FIG. 20 . 
     (Step S 104 ) The leverage management module  1203  judges whether the end-to-end capacity leverage ratio value  1902  in the end-to-end capacity leverage ratio information  1900  is higher than the end-to-end capacity leverage ratio threshold value  1911  in the initial settings information  1910 . If the value  1902  is judged to be higher than the threshold value  1911 , then step S 105  is executed, whereas if it is not higher, then step S 102  is executed. 
     (Step S 105 ) The leverage management module  1203  displays an alert which announces that the end-to-end capacity leverage ratio  1902  has risen sharply and the possibility of depletion of the physical storage capacity has increased. Moreover, the leverage management module  1203  displays a chart of the value of the end-to-end capacity leverage ratio  1902 , the storage level pool capacity  1402 , the storage level virtual volume identifier  1501  and the storage level virtual volume capacity  1502 , on the capacity leverage ratio display screen  1403  of the management program  1200 . The information reported on the display screen of the management program  1200  may be information other than that stated above, provided that the information is able to convey to the storage administrator the fact that the possibility of depletion of the physical capacity of the storage level pool  2220  has increased. 
     (Step S 106 ) On the other hand, if the result of the comparison shows that the end-to-end capacity leverage ratio  1902  has not exceeded the end-to-end capacity leverage ratio threshold value  1911 , then after the information gathering interval  1912  has elapsed, the procedure returns to step S 102 . 
     In the example described above, the storage level pool capacity  1402  and the server level virtual volume capacity  1802  were used in calculating the end-to-end capacity leverage ratio  1902 , but it is also possible to use other values from the tables to which these respective columns belong. 
     &lt;6-1-1. Capacity Information Gathering Process&gt; 
     Below, the details of the capacity information gathering process which is mentioned in overview in step S 102  in  FIG. 14  will be described. 
     (Step A) The storage management module  1201  gathers the identifier of the storage level virtual volume corresponding to the specified storage level pool identifier  1401 , from the storage level pool information  11000  held by the storage system  2000 , and stores the gathered identifier as the corresponding storage level virtual volume identifier  1404  in the storage level pool configuration information  1400 . 
     (Step B) The storage management module  1201  refers to the port/LUN correspondence information  1600  and acquires the port number  1601  and LUN  1602  allocated to the corresponding storage level virtual volume identifier  1404  which was gathered at step A. 
     (Step C) The server management module  1202  gathers the identifier of the server level pool  3210  corresponding to the storage level virtual volume  2230  allocated with the port number  1601  and LUN  1602  acquired by the storage management module  1201  at step B, from the server level pool information  15000  in the physical server  3000 , and stores this identifier as the server level pool identifier  1701  in the server level pool configuration information  1700 . The server level pool  3210  corresponding to the storage level virtual volume  2230  means the server level pool  3210  which has been set up so that the storage level virtual volume  2230  belongs thereto. 
     (Step D) The server management module  1202  gathers the identifiers and capacities of all of the server level virtual volumes  3220  corresponding to the gather server level pool identifier  1701 , from the server level pool information  15000  in the physical server  3000 . The server management module  1202  stores the identifiers of the server level virtual volumes  3220  as the corresponding server level virtual volume identifiers  1704  in the server level pool configuration information  1700  and as the server level virtual volume identifiers  1801  in the server level virtual volume configuration information  1800 . Furthermore, the respective server level virtual volume capacities are stored as the server level virtual volume capacity  1802  in the server level virtual volume configuration information  1800 . 
     &lt;6-1-2. Details of Processing for Calculating End-to-End Capacity Leverage Ratio&gt; 
       FIG. 15  is a flow diagram of the processing in step S 103  in  FIG. 14 . This processing is described below on the basis of the flow diagram. 
     (Step S 201 ) The leverage management module  1203  sends an inquiry to the storage system  2000  about the capacity of the storage level pool corresponding to the storage level pool identifier  1401  specified in (step A) of step S 102  under &lt;6-1-1. Capacity information gathering process&gt;. The storage system  2000  returns the data in the column, storage level pool capacity  11002 , of the storage level pool information  11000 , to the management server. The leverage management module stores the storage level pool capacity  11002  thus received as the storage level pool capacity  1402  in the storage level pool configuration information  1400 . 
     (Step S 202 ) The leverage management module  1203  adds up the server level virtual volume capacities  1802  gathered by the server management module  1202  in step D of step S 102  and stores the result as the corresponding server level virtual volume total capacity  1705  of the server level pool configuration information  1700 . 
     (Step S 203 ) The leverage management module  1203  calculates the ratio of the storage level pool capacity  1402  acquired at step S 201  to the value of the corresponding server level virtual volume total capacity  1705  calculated at step S 202  and stores the result of this calculation as the end-to-end capacity leverage ratio  1902  in the end-to-end capacity leverage ratio information  1900 . 
     The processing described above is premised on gathering capacity and displaying a leverage ratio in respect of a storage level pool indicated by the administrator, but it is also possible to display the leverage ratio in respect of a plurality of storage level pools which are managed by a management server. The processing in this case involves repeating the processes shown in  FIG. 15  and  FIG. 16  while the management server  1000  successively designates each one of a plurality of storage level pools  2220 , as the “specified storage level pool identifier  1401 ”. 
     Second Embodiment 
     7. Overview of Second Embodiment 
     In the computer system relating to a second embodiment of the present invention, in addition to the computer system of the first embodiment, if the end-to-end capacity leverage ratio  1902  exceeds an end-to-end capacity leverage ratio threshold value  1911  set by the storage administrator and it is judged that the risk of depletion of the physical storage capacity has increased, then the location which is the cause of the sudden rise in the end-to-end capacity leverage ratio  1902  is identified and information on the identified location is displayed to the storage administrator via a management screen of the management program. 
     Furthermore, in order to prevent depletion of the physical storage capacity, the management program  1200  implements processing for automatically changing the configuration of the storage system  2000 , thereby restricting the leverage ratio to a normal value which does not exceed the end-to-end capacity leverage ratio threshold value  1911 . 
     Furthermore, if a setup operation is accepted by a server virtualization program  3200  which includes a callback object, then that operation is interrupted (the storage control program  2500  may also include a callback object, described hereinafter, instead of or in addition to the server virtualization program  3200 ). The end-to-end capacity leverage ratio  1902  after execution of the accepted operation is simulated, and if it is judged that the end-to-end capacity leverage ratio  1902  would exceed the end-to-end capacity leverage ratio threshold value  1911  set by the storage administrator, then the management program  1200  automatically carries out configuration change processing for the storage system  2000 . By this means, it is possible to achieve a structure where the end-to-end capacity leverage ratio  1902  does not exceed the end-to-end capacity leverage ratio threshold value  1911  set by the storage administrator, even after the server virtualization program  3200  has executed the setup operation. When the processing described above has been carried out successfully by the management program  1200 , a success notification is sent to the server virtualization program  3200 , and upon receiving this notification, the server virtualization program  3200  restarts the accepted setup operation. On the other hand, if it is judged that the end-to-end capacity leverage ratio  1902  will not be restricted to the end-to-end capacity leverage ratio threshold value  1911  or lower even after the configuration change processing in the storage system  2000  is performed by the management program  1200 , then a notification is sent to the management program  1200  indicating that there is a high risk of depletion of the physical storage capacity by the setup operation, and a recommendation to halt the setup operation is issued. 
     &lt;7-1. Cause Location Identification Processing&gt; 
       FIG. 27  is a flow diagram of cause location identification processing. 
     If the end-to-end capacity leverage ratio  1902  calculated at step S 105  in &lt;6-1. Processing for calculating end-to-end capacity leverage ratio  1902 &gt; according to the first embodiment exceeds the end-to-end capacity leverage ratio threshold value  1911  set by the storage administrator and if it is judged that there is a high possibility of depletion of the physical storage capacity, then information indicating the location that is the cause of the steep rise in the end-to-end capacity leverage ratio  1902  is reported to the storage administrator via the display screen. 
     (Step S 401 ) The management program  1200  sends an inquiry to the storage system  2000  about the identifier of the storage level virtual volumes corresponding to the storage level pool  2220  in which the end-to-end capacity leverage ratio shows a sharp rise. Upon receiving this inquiry, the storage system  2000  returns the storage level virtual volume identifiers  11005  in the storage level pool information  11000 . The management program  1200  stores the received list of the identifiers of storage level virtual volumes  2230 , as the corresponding storage level virtual volume identifiers  1404 . 
     (Step S 402 ) The management program  1200  acquires the server level pool identifier  1701  corresponding to the respective storage level virtual volumes  2230  having the acquired storage level virtual volume identifiers  1404 . More specifically, for example, the management program  1200  refers to the port/LUN correspondence information  1600  and identifies the LUN  1603  corresponding to the identifier of the storage level virtual volume  2230 , which has been registered as an internal volume ID. The management program  1200  sends an inquiry to the physical server  3000  about the identifier of the server level pool  3210  corresponding to the LUN  1603 . Upon receiving this, the server virtualization program  3200  of the physical server  3000  identifies the LUN  1603  for which the inquiry has been made, from the configuration storage port number/LUN  1707 , and returns the corresponding server level pool identifier  15001  from the server level pool information  15000 , to the management server  1000 . The management program  1200  of the management server  1000  stores the received server level pool identifier  15001  as the server level pool identifier  1701  of the server level pool configuration information  1700 . 
     (Step S 403 ) The management program  1200  sends an inquiry to the physical server  3000  about the identifiers of the server level virtual volumes  3210  corresponding to the server level pool identifier  1701  acquired at step S 402 . Upon receiving this, the server virtualization program  3200  of the physical server  3000  returns the server level virtual volume identifiers  15004  corresponding to the server level pool identifier  1701  in the server level pool information  15000 , to the management server  1000 . The management program  1200  of the management server  1000  stores the received server level pool identifiers  15004  as the corresponding server level virtual volume identifiers  1704  in the server level pool configuration information  1700 . 
     (Step S 404 ) In respect of each of the server level virtual volumes  3220  having the respective corresponding server level virtual volume identifiers  1704  acquired at step S 403 , the management program  1200  sends an inquiry to the physical server  3000  about the capacity which has been mapped to the storage area of the server level pool  3210 , out of the server level virtual volume capacity  1802 . Upon receiving this, the server virtualization program  3200  of the physical server  3000  refers to the server level virtual volume information  16000  and returns the server level virtual volume allocated capacity  16003  corresponding to the server level virtual volume identifier  1704 , to the management server  1000 . The management program  1200  of the management server  1000  stores the received server level virtual volume allocated capacity  16003  as the server level virtual volume allocated capacity  1803  in the server level virtual volume configuration information  1800 . Moreover, the management program  1200  subtracts the value of the server level virtual volume allocated capacity  1803  from the server level virtual volume capacity  1802 , and stores the result as the server level virtual volume unallocated capacity  1804 . 
     (Step S 405 ) The management program  1200  compares the respective server level virtual volume unallocated capacities  1804  corresponding to the respective server level virtual volume identifiers  1801  calculated in step S 404 , and identifies the server level virtual volume  3220  having the highest value of the compared server level virtual volume unallocated capacities  1804  as a location causing sudden rise in the end-to-end capacity leverage ratio  1902 . The management program  1200  displays a screen showing information such as the identifier, capacity and unallocated capacity of this server level virtual volume  3220 .  FIG. 37  shows one example of this screen. According to the example in  FIG. 37 , the server level virtual volume mounted on the virtual machine (VM 4 ) is highlighted (for example, surrounded by a thick oval line) as a cause location. The method of indicating the cause location is not limited to the example shown in  FIG. 37 , and another method of indicating same may be used. 
     &lt;7-2. Normal Storage Configuration Change Processing&gt; 
       FIG. 16  is a flow diagram of storage configuration change processing. This processing is performed after carrying out the cause location identification processing. Each of the steps involved is described below. 
     (Step S 301 ) The management program  1200  checks whether or not there is a volume  2210  that has not been registered in the pool configuration volume identifiers  1406  of the storage level pool configuration information  1400 , in other words, whether there is a surplus volume  2210  which does not belong to a storage level pool  2220 , in the storage system  2000 . 
     (Step S 302 ) If there is a surplus volume  2210  in the storage system  2000  which does not belong to a storage level pool  2220 , then the management program  1200  automatically adds capacity to the storage level pool  2220  by newly setting the surplus volume  2210  to belong to the storage level pool  2220  having the storage level pool identifier  1401  specified in (step A) of step S 102  in &lt;6-1-1. Capacity information gathering process&gt; of the first embodiment. The capacity added to the storage level pool  2220  is set by the management program  1200  to a value whereby the end-to-end capacity leverage ratio  1902  is kept equal to or lower than the end-to-end capacity leverage ratio threshold value  1911 . The capacity added to the storage level pool  2220  may be set by the storage administrator on the management screen of the physical server  3000 . 
     (Step S 303 ) If, as a result of performing step S 302 , the end-to-end capacity leverage ratio  1902  is kept at or below the end-to-end capacity leverage ratio threshold value  1911  set by the storage administrator, then the procedure advances to step S 308 . If, on the other hand, the end-to-end capacity leverage ratio  1902  has exceeded the end-to-end capacity leverage ratio threshold value  1911 , then the procedure advance to step S 304 . 
     (Step S 304 ) If the end-to-end capacity leverage ratio  1902  has exceeded the end-to-end capacity leverage ratio threshold value  1911  in step S 303 , then the management program  1200  sends an inquiry to the storage system  2000  about whether there is a storage level pool  2220  other than the storage level pool  2220  in question, in the storage system  2000 . If there is another storage level pool, then the management program  1200  sends the storage system  2000  an inquiry with regard to the identifier of the storage level pool  2220  other than the storage level pool  2220  in question, which is the subject of the inquiry. The command control module  2503  of the storage system  2000  refers to the storage level pool information  11000  and returns a storage level pool identifier  11001  other than the identifier of the storage level pool  2220  in question, to the management server  1000 . The management program  1200  of the management server  1000  stores the received storage level pool identifier  11001  as a storage level pool identifier  1401  in the storage level pool configuration information  1400 , and then proceeds to step S 305 . If there is no other storage level pool, then the procedure advances to step S 308 . 
     (Step S 305 ) The management program  1200  refers to the end-to-end capacity leverage ratio information  1900  and specifies a storage level pool identifier  1401  having a low (for example, the lowest) end-to-end capacity leverage ratio  1902 . Image files in the server level virtual volume  3220  are migrated between the storage level pool  2220  in question and the storage level pool  2220  selected at step S 305 , in such a manner that the end-to-end capacity leverage ratio  1902  of the storage level pool  2220  in question becomes equal to or lower than the end-to-end capacity leverage ratio threshold value  1911 . In this case, the server level virtual volume  3220  to be migrated is specified as the server level virtual volume  3220  identified as a cause location of sudden rise in the end-to-end capacity leverage ratio at step S 405  in &lt;7-1. Cause location identification processing&gt;. This cause location may be specified automatically as an object for migration. Provided that the server level virtual volume  3220  forming the cause location is migrated to a server level virtual volume corresponding to another storage level pool, then the total capacity of the server level virtual volumes corresponding to the storage level pool which is the migration source decreases, and therefore the end-to-end capacity leverage ratio falls. In this case, desirably, the end-to-end capacity leverage ratio relating to the other storage level pool described above does not exceed the threshold value, even when the server level virtual volume  3220  forming the migration object is migrated. More specifically, for example, it is judged whether or not the end-to-end capacity leverage ratio relating to the other storage level pool exceeds the threshold value if the capacity of the server level virtual volume which is the migration object is added to the total capacity of the server level virtual volumes corresponding to the other storage level pool, and if it is judged that the threshold value is not exceeded, then the other storage level pool can be set as a migration destination. 
     (Step S 306 ) If, as a result of carrying out step S 305 , the end-to-end capacity leverage ratio  1902  of the storage level pool  2220  is kept at or below the end-to-end capacity leverage ratio threshold value  1911 , then the procedure advances to step S 308 . On the other hand, if the end-to-end capacity leverage ratio  1902  of the storage level pool  2220  has exceeded the end-to-end capacity leverage ratio threshold value  1911 , then the procedure advances to step S 307 . 
     (Step S 307 ) A notification is issued indicating that the end-to-end capacity leverage ratio  1902  has exceeded the end-to-end capacity leverage ratio threshold value  1911  set by the storage administrator, even after carrying out step S 302  and step S 305 . 
     (Step S 308 ) If the end-to-end capacity leverage ratio  1902  has been kept at or below the end-to-end capacity leverage ratio threshold value  1911  in step S 302  or step S 305 , then this fact is reported to the storage administrator. 
     &lt;7-3. Processing Carried Out by Management Program Using Callback Interface&gt; 
       FIG. 17  is a flow diagram showing processing carried out by a management program using a callback interface. 
     (Step S 501 ) The management program  1200  receives initial settings information  1910  which has been input by the storage administrator via the setup screen of the management program  1200 . The threshold value of the end-to-end capacity leverage ratio is input to the initial settings information  1910 . The management program  1200  stores the input threshold value as the end-to-end capacity leverage ratio threshold value  1911  in the initial settings information  1910 . 
     (Step S 502 ) Next, a callback process is carried out. The details of the callback process are described here with reference to  FIG. 19 . 
       FIG. 19  is a flow diagram of a callback process. 
     (Step S 601 ) The server virtualization program  3200  registers the address of the management program  1200 . 
     (Step S 602 ) Upon accepting a setup operation event, the server virtualization program  3200  sends a callback object to the management program  1200 . The callback object includes the total capacity of the server level virtual volumes  3220  before the execution of the setup operation, and the contents of the setup operation. 
     (Step S 603 ) The management program  1200  waits for a callback object to be sent from the server virtualization program  3200 , and when a callback object arrives from the server virtualization program  3200 , the management program  1200  receives this object. 
     (Step S 604 ) The management program  1200  calculates the total capacity of the server level virtual volumes  3220  after executing the operation accepted by the server virtualization program  3200 , by simulation on the basis of the information included in the received callback object. 
     (Step S 605 ) The management program  1200  identifies the storage level pool  2220  corresponding to the server level virtual volumes  3220  relating to the setup operation. The concrete steps are as follows. 
     (Step A) The server management module  1202  sends an inquiry to the physical server  3000  about the identifier of the server level pool  3210  which corresponds to the identifier  1801  of the server level virtual volumes relating to the setup operation. Upon receiving this, the server virtualization program  3200  of the physical server  3000  refers to the server level virtual volume information  16000  and returns a server level pool identifier  16004 . The management program  1200  stores the server level pool identifier  16004  thus received as the corresponding server level virtual volume identifier  1806  in the server level virtual volume configuration information  1800 . 
     (Step B) Thereupon, the management program  1200  refers to the server level pool configuration information  1700  and identifies a server level pool identifier  1701  which is the same as the corresponding server level pool identifier  1806  in step A. The management program  1200  then sends an inquiry to the physical server  3000  in respect of the storage port number/LUN  1707  corresponding to the identified server level pool  3210 . Upon receiving this, the server virtualization program  3200  of the physical server  3000  refers to the server level pool information  15000  and returns a configuration storage port number/LUN  15006  to the management server  1000 . The management program  1200  of the management server  1000  stores the received configuration storage port number/LUN  15006  as the configuration storage port number/LUN  1707  of the server level pool configuration information  1700 . 
     (Step C) Thereupon, the management program  1200  refers to the port/LUN correspondence information  1600  and acquires the internal volume ID  1601  corresponding to the configuration storage port number/LUN  1707  acquired in step B. 
     (Step D) Thereupon, the management program  1200  refers to the storage level virtual volume configuration information  1500  and identifies a storage level virtual volume  2230  having the same identifier as the internal volume ID  1601 . The management program  1200  then acquires the corresponding storage level pool identifier  1504  which corresponds to the identified storage level virtual volume  2230 . 
     The description now returns to  FIG. 17 . 
     (Step S 503 ) The leverage management module  1203  of the management program  1200  carries out processing for calculating the end-to-end capacity leverage ratio by using the total capacity of the server level virtual volumes  3220  obtained by the callback process, and the capacity information relating to the identified storage level pool  2220 . The details of the process for calculating the end-to-end capacity leverage ratio are described later with reference to  FIG. 20 . 
     (Step S 504 ) The leverage management module  1203  judges whether the value of the end-to-end capacity leverage ratio  1902  in the end-to-end capacity leverage ratio information  1900  is higher than the end-to-end capacity leverage ratio threshold value  1911  in the initial settings information  1910 . If the value  1902  is judged to be higher than the threshold value  1911 , then step S 505  is executed, whereas if it is not higher, then step S 502  is executed. 
     (Step S 505 ) The leverage management module  1203  displays an alert which announces that the end-to-end capacity leverage ratio  1902  has risen sharply and the possibility of depletion of the physical storage capacity has increased. Moreover, the leverage management module  1203  displays a chart of the value of the end-to-end capacity leverage ratio  1902 , the storage level pool capacity  1402 , the storage level virtual volume identifier  1501  and the storage level virtual volume capacity  1502 , to the storage administrator, on the capacity leverage ratio display screen  1403  of the management program  1200 . The information reported on the display screen of the management program  1200  may be information other than that stated above, provided that the information is able to convey to the storage administrator the fact that the possibility of depletion of the physical capacity of the storage level pool  2220  has increased. 
     In the example described above, the storage level pool capacity  1402  and the server level virtual volume capacity  1802  were used in calculating the end-to-end capacity leverage ratio  1902 , but it is also possible to use other values from the tables to which these respective columns belong. 
     &lt;7-3-1. Details of Processing for Calculating End-to-End Capacity Leverage Ratio in Callback Process&gt; 
       FIG. 20  is a flow diagram of the processing in step S 503  in  FIG. 17 . 
     (Step S 801 ) The leverage management module  1203  refers to the storage level pool configuration information  1400  and acquires the storage level pool capacity  1402  corresponding to the storage level pool identifier  1401  specified in step S 605 . 
     (Step S 802 ) The leverage management module  1203  calculates the ratio of the storage level pool capacity  1402  acquired at step S 201  under &lt;7-3. Processing performed by management program using callback interface&gt; to the value of the corresponding server level virtual volume total capacity  3220  calculated at step S 604 , and stores the result of this calculation as the end-to-end capacity leverage ratio  1902  in the end-to-end capacity leverage ratio information  1900 . 
     The processing described above is premised on gathering capacity and displaying an end-to-end leverage ratio in respect of a storage level pool  2220  indicated by the storage administrator, but it is also possible to display the leverage ratio in respect of a plurality of storage level pools  2220  which are managed by a management server  1000 . The processing in this case involves repeating the processes shown in  FIG. 19  and  FIG. 20  while the management server  1000  successively designates each one of a plurality of storage level pools  2220 , as the “specified storage level pool identifier  1401 ”. 
     &lt;7-4. Storage Configuration Change Processing in Callback Process&gt; 
       FIG. 18  is a flow diagram of storage configuration change processing in a case where the management program  1200  is provided with a callback interface. This flow is executed from the steps in  FIG. 14 . 
     (Step S 701 ) The management program  1200  checks whether or not there is a volume  2210  that has not been registered in the pool configuration volume identifiers  1406  in the storage level pool configuration information  1400 , in other words, a surplus volume  2210  which does not belong to a storage level pool  2220 , in the storage system  2000 . 
     (Step S 702 ) If there is a surplus volume  2210  in the storage system  2000  which does not belong to a storage level pool  2220 , then the management program  1200  automatically adds capacity to the storage level pool  2220  by newly setting the surplus volume  2210  to belong to the storage level pool  2220  having the storage level pool identifier  1401  acquired in step S 201  in &lt;7-3. Processing performed by management program using callback interface&gt;. The capacity added to the storage level pool  2220  is set by the management program  1200  to a value whereby the end-to-end capacity leverage ratio  1902  is kept at or below the end-to-end capacity leverage ratio threshold value  1911 . The capacity added to the storage level pool  2220  may be set by the storage administrator on the management screen of the physical server  3000 . 
     (Step S 704 ) If the end-to-end capacity leverage ratio  1902  has exceeded the end-to-end capacity leverage ratio threshold value  1911  in step S 703 , then the management program  1200  refers to the storage level pool configuration information  1400  and checks whether there is a storage level pool  2220  other than the storage level pool  2220  in question, in the storage system  2000 . If there is another storage level pool, then the procedure advances to step S 705 . If there is no other storage level pool, then the procedure advances to step S 708 . 
     (Step S 705 ) The management program  1200  refers to the end-to-end capacity leverage ratio information  1900  and specifies a storage level pool identifier  1401  having a low (for example, the lowest) end-to-end capacity leverage ratio  1902 . Image files in the server level virtual volume  3220  are migrated between the storage level pool  2220  in question and the storage level pool  2220  selected at step S 705 , in such a manner that the end-to-end capacity leverage ratio  1902  of the storage level pool  2220  in question becomes equal to or lower than the end-to-end capacity leverage ratio threshold value  1911 . The server level virtual volume  3220  migrated in this case is specified by the management program  1200  referring to the server level virtual volume configuration information  1800  and setting the volume having the highest server level virtual volume unallocated capacity  1804 . 
     (Step S 706 ) If, as a result of carrying out step S 305 , the end-to-end capacity leverage ratio  1902  of the storage level pool  2220  is kept at or below the end-to-end capacity leverage ratio threshold value  1911 , then the procedure advances to step S 708 . On the other hand, if the end-to-end capacity leverage ratio  1902  of the storage level pool  2220  exceeds the end-to-end capacity leverage ratio threshold value  1911 , then the procedure advances to step S 707 . 
     (Step S 707 ) The management program  1200  sends the server virtualization program  3200  a recommendation to halt the setup operation, because there is a high risk of depletion of the storage capacity by executing the setup operation that the server visualization program  3200  is seeking to perform. Upon receiving this, the server visualization program  3200  reconfirms to the server administrator whether or not the setup operation is to be carried out. 
     (Step S 708 ) The management program  1200  reports to the server virtualization program  3200  that the setup operation it is seeking to carry out is safe. Upon receiving this, the server virtualization program  3200  restarts the setup operation which had been interrupted. 
     (Step S 709 ) The management program  1200  reports to the storage administrator that there is a high possibility of depletion of the storage capacity. 
     (Step S 710 ) The management program  1200  notifies the storage administrator that the possibility of depletion of the storage capacity that had increased sharply is now reduced and displays capacity information for the storage level pool  2220 , and the like, of which the configuration has been changed. 
     In the foregoing, several embodiments of the present invention were described, but the present invention is not limited to these embodiments and may of course be modified in various ways without departing from the essence of the invention. 
     For example, the management server  1000  may carry out processing for making the end-to-end capacity leverage ratio equal to or less than a threshold value (for example, addition of capacity to the storage level pool or migration of a server level virtual volume), without displaying the end-to-end capacity leverage ratio (and/or without displaying other management information). 
     Furthermore, for example, as shown in  FIG. 38 , the management server  1000  may display a screen showing both the end-to-end capacity leverage ratio of the storage level pool and the free capacity ratio of the storage level pool, side by side. The free capacity ratio is, for example, the ratio of the unallocated capacity of the storage level pool with respect to the capacity of the storage level pool (the difference between the capacity of the storage level pool and the allocated capacity of the storage level pool). 
     Moreover, for example, although not shown in the drawings, the management server  1000  may manage the change in the free capacity ratio of the storage level pool (the free capacity ratio at respective time points) and show information representing that change, and calculate and display a recommended end-to-end capacity leverage ratio threshold value for the storage level pool. 
     Furthermore, the end-to-end capacity leverage ratio threshold value may be different for each storage level pool. More specifically, for example, it is possible to prepare, for each storage level pool, an end-to-end capacity leverage ratio threshold value which is set on the basis of the change in the free capacity ratio of the storage level pool (the speed at which the free capacity ratio decreases). Furthermore, respective threshold values may be prepared for different types of leverage ratio. 
     Third Embodiment 
     8. Overview of Third Embodiment 
     The computer system relating to a third embodiment of the present invention relates to capacity management of the storage system in accordance with the deletion of a virtual machine, and in particular, to the releasing of the area (LL-SA) of a volume that has become unnecessary. In addition to deleting a virtual machine for reasons relating to the end-to-end capacity leverage ratio according to the first and second embodiments as described below, a virtual machine may also be deleted for reasons unrelated to the end-to-end capacity leverage ratio. It is necessary for all of the following conditions to be established. 
     Reasons for deleting virtual machine relating to end-to-end capacity leverage ratio: 
     (Reason 1) A virtual machine defined in the past is deleted as a measure for reducing the end-to-end capacity leverage ratio which has risen excessively. 
     Reasons for deleting virtual machine unrelated to end-to-end capacity leverage ratio: 
     (Reason 2) A virtual machine judged to be unnecessary is deleted in order to increase the unallocated area of the storage level pool and the server level pool. 
     (Reason 3) Application processing which has been executed on a virtual machine is switched to execution by a physical server, due to reasons of improving reliability and processing performance, etc., and the virtual machine therefore has become unnecessary. 
     (Reason 4) A virtual machine ceases to be used, due to the person who was using the virtual machine being transferred or retiring, or the end of the contract of use of the virtual machine. 
     Of course, there may also be other reasons for deleting a virtual machine. 
       FIG. 41  is a schematic drawing showing an example of the correspondences between virtual machines  3201 , server level virtual volumes (HL-VVOL)  3220 , the server level pool (HLP)  3210 , storage level virtual volumes (LL-VVOL)  2230 , the storage level pool (LLP)  2220 , and volumes (VOL)  2210 . The sever recognition LU  3211  corresponds to a storage level virtual volume  2230 , and is stated in order to indicate that there is a difference between the HL-SA size  15007  in the server management program  3200  (the information in the server level pool information  15000 ), and the LL-SA size  11007  in the storage system (the information in the storage level pool information  11000 ). 
     The example in  FIG. 41  shows the following situation. 
     The volume (VOL 1 )  2210  includes one area (LL-SA) in a volume of the same capacity as the LL-SA size  11007 , and the volume (VOL 2 )  2210  includes two areas (LL-SA) in a volume having twice the capacity of the LL-SA size  11007 . 
     The volume (VOL 1 )  2210  and the volume (VOL 2 )  2210  are included in the storage level pool  2220 , and LL-VVOL 1  to LL-VVOL 3  are defined as storage level virtual volumes  2230  using this storage level pool. 
     The storage level virtual volume (LL-VVOL 1 )  2230  is provided to the physical server as a virtual volume which has a capacity of twice the LL-SA size  11007  (in other words, a virtual volume containing two areas (LL-AA)). 
     At a certain point in time, the area (LL-SA) of the volume (VOL 1 )  2210  is allocated to the first area (LL-AA) of the storage level virtual volume (LL-VVOL 1 )  2230 , and the area (LL-SA) of the volume (VOL 2 )  2210  is allocated to the second area (LL-AA). 
     As indicated by  3211  in the figure, the server virtualization program  3200  includes the storage level virtual volume (LL-VVOL 1 ) in the server level pool  3210  and manages the storage level virtual volume (LL-VVOL 1 ) by dividing into units of the HL-SA size  15007 . The capacity of the storage level virtual volume (LL-VVOL 1 )  2230  is four times the HL-SA size. 
     The server level virtual volume (HL-VVOL 1 )  3220  is provided to the virtual machine (VM 1 )  3201  as a virtual volume which has a capacity of three times the HL-SA size  15007  (in other words, a virtual volume containing three areas (HL-AA)). 
     The server level virtual volume (HL-VVOL 2 )  3220  is provided to the virtual machine (VM 2 )  3201  as a virtual volume which has a capacity of three times the HL-SA size  15007  (in other words, a virtual volume containing three areas (HL-AA)). 
     At a certain point in time, areas (HL-SA) of the storage level virtual volume are allocated to all of the areas (HL-AA) of the server level virtual volume (HL-VVOL 1 )  3220 . 
     At a certain point in time, an area (HL-SA) of the storage level virtual volume is allocated to one of the area (HL-AA) of the server level virtual volume (HL-VVOL 2 )  3220 . 
       FIG. 42  shows a schematic view of a computer system after the server virtualization program  3200  has received a virtual machine deletion request specifying the virtual sever (VM 1 )  3201 . 
     In response to the virtual machine deletion request, the server virtualization program  3200  erases the information constituting the virtual machine (VM 1 )  3201  (for example, the definition file, memory image, etc.) and also releases the areas (HL-SA) which were allocated to the server level virtual volume (HL-VVOL 1 ). Release of the areas (HL-SA) by the server virtualization program  3200  means that the identifiers of the areas (HL-SA) in question are added to the unallocated HL-SA identifier list in the server level pool information  15000 , and this indicates that these areas (HL-SA) can subsequently be reallocated by another virtual machine. 
     The storage control program  2050  in the storage system  2000  identifies the areas (LL-AA) of the storage level virtual volume  2230  (LL-VVOL 1 ) corresponding to the areas (HL-SA) that have been released, and duly releases the areas (LL-SA) that were allocated to the identified areas (LL-AA). Release of the areas (LL-SA) by the storage control program  2050  means that the identifiers of the areas (LL-SA) in question are added to the unallocated LL-SA identifier list in the storage level pool information  11000 , and this indicates that these areas (LL-SA) can subsequently be reallocated by another virtual machine. 
     However, if the HL-SA area length in the server virtualization program  3200  and the LL-SA area length in the storage control program  2050  are not matching, then as shown in  FIG. 43 , the areas (LL-SA) of the volume  2210  are not necessarily released in accordance with the capacity of the areas (HL-SA) released by the server virtualization program  3200 . One example of a reason why the HL-SA area length in the server virtualization program  3200  and the LL-SA area length in the storage control program  2050  may not be matching is described below. 
     Storage level virtual volumes  2230  having a larger capacity than the server level virtual volumes  3220  provided by one physical server are provided frequently, and the number of physical servers accessing the storage system is high. Therefore, by consequently making the LL-SA area length a larger value than the HL-SA area length, the information volume of the storage level pool information  11000  (and in particular, the unallocated LL-SA identifier list  11008 ), and the storage level virtual volume information  12000  (and in particular, the LL-area conversion information  12007 ) is reduced. 
       FIG. 43  depicts the difference between the areas (HL-SA) released by the server virtualization program  3200  upon deletion of a virtual machine, and the areas (LL-SA) released by the storage control program  2050 . More specifically, the release of an area (LL-SA) of a volume  2210  needs to be carried out after all of the areas (HL-SA) used by that area (LL-SA) have been released by the server virtualization program  3200 . If the area (LL-SA) of the volume (VOL 2 ) in the drawing is released first, then the area (HL-SA) which has been allocated to the storage level virtual volume (HL-VVOL 2 ) that is not the release target, will also be released. 
     &lt;8-1. Virtual Machine Deletion Process&gt; 
     Next, the process for releasing an area (LL-SA) in accordance with the deletion of a virtual machine according to a third embodiment of the present invention will be described with reference to  FIG. 44 . 
     &lt;8-1a. Processing in Response to Deletion Request&gt; 
     (Step S 44001 ) The server virtualization program  3200  receives a virtual machine deletion request from the management server  1000  or other computer. The virtual machine deletion request includes the identifiers of one or more virtual machines which are objects for deletion. 
     (Step S 44002 ) The server virtualization program  3200  refers to the server level pool information  15000  and identifies the server level virtual volume corresponding to the virtual machine which is the deletion object. Furthermore, the program also refers to the server level virtual volume information  16000  and identifies the areas (HL-SA) allocated to the identified server level virtual volume. The areas (HL-SA) which contain the settings information, memory images, and the like, of the virtual machine forming the deletion object can be treated as the identified areas (HL-SA). Furthermore, it is also possible for areas (HL-SA) which are shared with another virtual machine to be omitted from the identified areas (HL-SA). 
     (Step S 44003 ) The server virtualization program  3200  deallocates the areas (HL-SA) identified in step S 44002  and deletes the server level virtual volume identified at step S 44002 . A more specific description of the related information handling is given below. 
     The identified areas (HL-SA) are added to the unallocated HL-SA identifier list  15008  in the server level pool information  15000 , and the server level pool allocated capacity  15003  is reduced by the capacity of these added areas (HL-SA). 
     The total capacity of the sever level virtual volumes in the server level pool information  15000  is reduced by the capacity of the identified sever level virtual volume (needless to say, this calculation alters the end-to-end capacity leverage ratio). 
     The information on the identified server level virtual volume is deleted from the server level virtual volume information  16000 . 
     Aside from these processes, it is also possible to carry out general virtual machine deletion processing. 
     (Step S 44004 ) The server virtualization program  3200  identifies the SCSI address (LUN, block address and block length) of the areas (HL-SA) identified in step S 44002 , and sends a region release instruction specifying the identified SCSI address to the storage system  2000 . The following modes can be envisaged for issuing a region release instruction. Firstly, there is a mode where the instruction from the server virtualization program  3200  is issued to the storage system  2000  via the management server  1000 . More specifically, the server virtualization program  3200  issues an API (Application Programming Interface) including the SCSI address of the identified areas (HL-SA) to the management server  1000  via a LAN  5010 . Thereupon, the management server  1000  issues an API containing the received SCSI address to the storage system  2000  via the LAN  5010 . Secondly, there is a mode where the server virtualization program  3200  issues an API including the SCSI address of the identified areas (HL-SA) directly to the storage system  2000  via a LAN  5010 . Thirdly, there is a mode where the server virtualization program  3200  issues an API including the SCSI address of the identified areas (HL-SA) directly to the storage system  2000  via a SAN  5000 . The destination of the API may be a specific LL-VOL which is to receive the API, or a LL-VOL which is the object of region release. Furthermore, the API may be a WRITE SAME command, which is a SCSI command for repeatedly writing continuous data, or an UNMAP command which is a SCSI command for reporting an unnecessary region. 
     (Step S 44101 ) The storage control program  2050  receives a region release instruction. 
     (Step S 44102 ) The storage control program  2050  identifies the block address range on the storage level virtual volume corresponding to the SCSI address specified by the region release instruction. The program then changes the data of the identified block address range to clear values (for example, zeros). The process for changing to clear values is similar to the process of writing storage data to the specified block address range. 
     (Step S 44103 ) The storage control program  2050  identifies a volume area (LL-SA) allocated to the area (LL-AA) which is contained completely within the block address range on the storage level virtual volume specified at step S 44102 . The program refers to the storage level virtual volume information  12000  and the storage level pool information in order to make this identification. 
     (Step S 44104 ) The storage control program  2050  releases the volume area (LL-SA) identified in step S 44103 . A more specific description of the related information handling is given below. 
     The identified area (LL-SA) is added to the unallocated LL-SA identifier list  11008  in the storage level pool information  11000 , and the storage level pool allocated capacity  11003  is reduced by the capacity of the area (LL-SA) which has been added to the list  11008 . 
     In the LL-area conversion information  12007  of the storage level virtual volume information  12000 , the value listed for the area (LL-AA) to which the specified area (LL-SA) was allocated is updated to “unallocated”. 
     The storage control program  2050  waits for the completion of the processing described above and then sends a region release instruction completion report to the physical server  3000 . The server virtualization program receives the region release instruction completion report and ends the virtual machine deletion process. The address specified by the region release instruction may be an address other than a SCSI address, and the operation of updating the completely contained area (LL-AA) to clear values in the step S 44103  may be omitted. 
     &lt;8-1b. Repeat Execution Processing&gt; 
     By repeatedly executing step S 44201  described below, the storage control program  2050  attempts to release the allocation of an area (LL-AA) comprising a block address range which is included in the block address range specified in step S 44102  but is not included in the area (LL-AA) specified in step S 44103 . 
     (Step S 44201 ) The storage control program  2050  searches for an area (LL-SA) having all data set to clear values, in the areas (LL-SA) allocated to the area (LL-AA) of the storage level virtual volume, and if this search is successful, releases the area (LL-SA) thus found from the area (LL-AA) to which it was allocated. The handling of information in relation to release is similar to that of step S 44104 . 
     If the areas (LL-SA) have a large size, then a correspondingly long time is required for the process of checking that each individual area (LL-SA) is set entirely to clear values, and the data in the areas (LL-SA) may be updated during this checking process. The following countermeasures can be applied in this respect. 
     (Countermeasure 1): It is made possible to set an additional flag which indicates “checking of clear values in progress”, in the listed values of the LL-area conversion information  12007 . 
     (Countermeasure 2): Before checking the clear values in step S 44201 , a flag indicating “checking of clear values in progress” is set at a corresponding location in the list of LL-area conversion information relating to the area (LL-AA) to which the area (LL-SA) being checked was allocated. 
     (Countermeasure 3): If an area (LL-SA) having all clear values is found at step S 44201 , then a release operation is carried out only if a “checking of clear values in progress” flag is raised for the area (LL-AA) to which the found area (LL-SA) was allocated, and the flag is then lowered. 
     (Countermeasure 4): When data is written to an area (LL-AA) for which a “checking of clear values in progress” flag has been raised in the storage data writing process, the flag is lowered. 
     The processing in step S 44201  is carried out in coordination with step S 44104 , in respect of the area (LL-SA) allocated to the area (LL-AA) comprising the block address range identified in step S 44102 , which has not been set as an object for release in step S 44104 . 
     The foregoing is a virtual machine deletion process. As shown in  FIG. 24 , since a clear value is returned if a read operation is performed to the area (LL-AA) to which the released area (LL-SA) was allocated, then the server virtualization program  3200  is able to reuse that area subsequently without problem. Furthermore, if a plurality of virtual machines are to be deleted, then from the viewpoint of releasing the areas (LL-SA), better release efficiency is achieved if the plurality of virtual machines are specified together in the deletion request. This is because, if the virtual machines are each specified separately, then release is attempted in step S 44201  without step S 44104  being applicable, whereas if the virtual machines are specified together, then the probability of completely containing the area is raised and the areas (LL-SA) to which step S 44104  applies are increased. 
     &lt;8-2. Management Server Display&gt; 
       FIG. 45  shows a display screen of the management server  1000  in relation to virtual machine deletion. The following information is shown on this screen. 
     The date and time that the virtual machine was deleted  45001 . 
     The identifier(s) of the one or more virtual machines deleted  45002 . 
     The total capacity of the server level virtual volume that was used by the deleted virtual machine(s)  45003 . 
     The difference in the allocated capacity of the server level pool caused by the deletion request  45004 . Since the allocated capacity always decreases with a deletion request, then this value is negative. 
     The difference in the allocated capacity of the storage level pool caused by the deletion request  45005 . Since the allocated capacity always decreases with a deletion request, then this value is negative. 
     The information elements  45001  and  45002  can be found out readily in cases where the management server  1000  has issued the virtual machine deletion request. On the other hand, in cases where a computer other than the management server  1000  has issued the virtual machine deletion request, the virtual machine identifiers specified by the virtual machine deletion request, and the reception date and time, should be acquired from the physical server  3000 . The information elements  45003  to  45005  can be acquired by comparing the storage level pool configuration information  1400 , the server level pool configuration information  1700  and the server level virtual volume configuration information held by the management server  1000  before and after the virtual machine deletion request. However, these information elements can also be acquired by methods other than these. 
     In the description given above, the management server  1000  creates settings information (for example, storage level pool configuration information  1400 , storage level virtual volume configuration information  1500 , port/LUN correspondence information  1600 , server level pool configuration information  1700  and server level virtual volume configuration information  1800 ) by gathering information on the settings applied in the storage system  2000  and physical server  3000 , from the storage system  2000  and the physical server  3000 , and the management server  1000  calculates and displays an end-to-end capacity leverage ratio. However, if the management server  1000  establishes settings for the storage system  2000  and the physical server  3000  on the basis of setting values received from an administrator or a data source apparatus (for example, a portable storage medium) via an input/output device  4060 , then the process of acquiring all or a part of the aforementioned settings information from the storage system  2000  and physical server  3000  can be omitted, the settings information described above can be created or updated on the basis of these settings values, and the end-to-end capacity leverage ratio can be calculated and displayed accordingly. In the latter case, it is possible to assist the setup process performed by the administrator by displaying the end-to-end capacity leverage ratio before the settings based on the settings value are applied to the storage system  2000  or the physical server  3000 . 
     In respect of the portion which has been described using block addresses, apart from an I/O request from a virtual machine and an I/O request sent to the storage system  2000  from a physical server  3000 , it is also possible to employ addressing in other units, or separate addresses using a prescribed conversion. 
     DESCRIPTION OF THE SYMBOLS 
     Reference Signs List 
       2000  Storage system