Patent Publication Number: US-2022222220-A1

Title: Hierarchical storage management system, hierarchical storage control apparatus, hierarchical storage management method and program

Description:
TECHNICAL FIELD 
     The present invention relates to a technique for optimizing data storage and operation by arranging data stored in a plurality of data centers based on conditions determined by a business operator. 
     BACKGROUND ART 
     A conventional hierarchical storage management system has large-capacity storage configured by using SSDs, HDDs, and magnetic tapes in accordance with the number of reference counts made to stored data and the access speed (write, read) of a storage medium. Data having the high number of reference counts is automatically stored in an SSD to achieve a higher access speed (Non Patent Literature 1). 
     In addition, there is a content distribution system that can shorten download time by providing a content cache server at the boundary between a user area and a public network and downloading a content from the cache server close to an accessing user (Non Patent Literature 2). 
     Furthermore, thin clients, software-defined storage employing virtualization, etc. have become widespread, and data is managed in data centers without ensuring storage in client terminals of the users (Non Patent Literature 3). 
     CITATION LIST 
     Non Patent Literature 
     [NPL 1] https://www.atmarkit.co.jp/ait/articles/1106/27/news109.html 
     [NPL 2] https://blog.redbox.ne.jp/what-is-cdn.html 
     [NPL 3] https://www.atmarkit.co.jp/ait/articles/1409/29/news130.htm 
     SUMMARY OF THE INVENTION 
     Technical Problem 
     In recent year, instead of holding and managing software, data, etc. in computer hardware, users have come to manage software, data, etc. on a server in a data center connected to a network, and with the increasing capacity and speed of communication networks, the spread of SNS, the revision of the Electronic Document Law, etc., there has been an increasing demand for storing large volumes of data with different purposes on the network. 
     Accordingly, a large amount of data of various sizes is stored in the data center for an extended period of time. Among various types of data, there is data for which delay is not allowed, data for which delay is allowed but power consumption and costs need to be reduced, etc. However, to store each of the data having such various operation policies in an appropriate storage medium, the processing needs to be performed manually in the prior art, and thus takes a great deal of time and effort. 
     The present invention has been made with the foregoing in view, and it is an object to provide a technique capable of automatically selecting a storage medium that matches an operation policy of data from a plurality of storage media disposed in a plurality of data centers. 
     Means for Solving the Problem 
     According to the disclosed technique, there is provided a hierarchical storage management system including: a hierarchical storage that is provided in an individual data center and has at least one storage medium; and a hierarchical storage control apparatus that manages at least one hierarchical storage, wherein the hierarchical storage control apparatus includes a calculation unit that performs processing for obtaining, for individual data managed by the hierarchical storage control apparatus, a storage medium in a data center that satisfies an operation policy by calculating power consumption needed for storing the data, a cost needed for storing the data, and communication time for transferring the data from a data center to a reference source area and by comparing the calculated power consumption, cost, and communication time with the operation policy set for the data. 
     Effects of the Invention 
     According to the disclosed technique, there is provided a technique capable of automatically selecting a storage medium that matches an operation policy of data from a plurality of storage media disposed in a plurality of data centers. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  illustrates a configuration of a hierarchical storage management system. 
         FIG. 2  illustrates a configuration of a hierarchical storage. 
         FIG. 3  illustrates a configuration a hierarchical side storage control apparatus. 
         FIG. 4  is a diagram illustrating an example of a hardware configuration of the apparatus. 
         FIG. 5  is diagram illustrating a structure of a data center information table. 
         FIG. 6  is a diagram illustrating a structure of a storage medium information table. 
         FIGS. 7( a ) to 7( c )  are diagrams illustrating structures of various tables. 
         FIG. 8  is a diagram illustrating a structure of an operation policy table. 
         FIG. 9  is a diagram illustrating a structure of a stored data management table. 
         FIG. 10  is a flowchart illustrating calculation performed by a hierarchical storage control apparatus. 
         FIG. 11  is a diagram illustrating a data center arrangement according to an embodiment. 
         FIG. 12  illustrates a configuration of a hierarchical storage control system according to the embodiment. 
         FIG. 13  is a diagram illustrating data center information table according to the embodiment. 
         FIG. 14  is a diagram illustrating a storage medium information table according to the embodiment. 
         FIGS. 15( a ) to 15( c )  are diagrams illustrating various tables according to the embodiment. 
         FIG. 16  is a diagram illustrating an operation policy table according to the embodiment. 
         FIG. 17  is a diagram illustrating a stored data management table according to the embodiment. 
         FIG. 18  is a diagram illustrating a calculation example. 
         FIG. 19  is a diagram illustrating a calculation example. 
         FIG. 20  is a diagram illustrating a calculation example. 
         FIG. 21  is a diagram illustrating a calculate result. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, an embodiment of the present invention (the present embodiment) will be described with reference to the drawings. The embodiment described below is merely an example. An embodiment to which the present invention is applied is not limited to the following embodiment. 
     The present embodiment describes a technique for automatically selecting, for individual data to be stored in a plurality of data centers, a storage medium that matches an operation policy of the data, by referring to the location conditions (construction cost, electricity charges), the data reference frequency and the communication speed of the network, and the type of the storage medium storing the data and the installation location of the storage medium. This technique reduces unnecessary power consumption and a cost and contributes to reductions of the power consumption (improvement in energy-saving properties) and the cost in a cloud-type data center and a virtualized NW as well as to improvement of QoS. Hereinafter, the technique will be specifically described. 
     (Overall System Configuration) 
       FIG. 1  illustrates a configuration of a hierarchical storage management system according to the present embodiment. As illustrated in  FIG. 1 , the hierarchical storage management system according to the present embodiment includes a hierarchical storage control apparatus  20  and a plurality of data centers  30  each connected to a network  10 . In addition, a user  50  is connected to the network  10 . The “user  50 ” is, for example, a client terminal used by a user. 
     As illustrated in  FIG. 1 , a hierarchical storage  40  is disposed in each of the data centers  30 . A data center operator or a CDN operator stores its own data or data of the user  50  in the hierarchical storage  40  disposed in any one of the data centers  30 . 
     The hierarchical storage  40  in the plurality of data centers  30  and the hierarchical storage control apparatus  20  are connected via at least one network  10  so that large-scale storage can be provided. 
     For example, a storage medium of the hierarchical storage  40  in the data center  30  located near an urban area where the land price is high is configured mainly by a high-speed storage medium such as an SSD and stores data that has a high reference frequency and requires a short delay time. In contrast, a storage medium of the hierarchical storage  40  in the data center  30  located in a suburban area where the land price is low is configured mainly by a plurality of storage media with a low speed such as a magnetic tape to achieve an ultra-high capacity and stores data that has a low reference frequency and allows delay. 
     When the user  50  refers to data, the data is downloaded from the hierarchical storage  40  in which the data is stored to the user  50 . 
     (Configuration of Hierarchical Storage  40 ) 
       FIG. 2  illustrates a configuration of the hierarchical storage  40  disposed in the data center  30 . As illustrated in  FIG. 2 , the hierarchical storage  40  includes a storage unit  410 , constituted of a plurality of storage media  420  # 1  to  420  #n, and a management unit  430 . 
     The individual storage medium  420  is, for example, an SSD (flash memory), an HDD (magnetic disk), an optical disk, a magnetic tape, or the like. The management unit  430  checks the input and output of data and detects a reference source area and the number of cumulative reference counts when stored data is referred to. The detected information is notified to the hierarchical storage control apparatus  20  and managed therein. 
     (Configuration of Hierarchical Storage Control Apparatus  20 ) 
       FIG. 3  illustrates a configuration of the hierarchical storage control apparatus  20 . As illustrated in  FIG. 3 , the hierarchical storage control apparatus  20  includes a calculation unit  210 , a storage unit  220 , and a timer  230 . 
     The storage unit  220  stores a data center information table  2210 , a storage medium information table  2220 , a transmission line information table  2230 , a calculation interval table  2240 , an execution log table  2250 , an operation policy table  2260 , and a stored data management table  2270 . 
     The timer  230  holds current date and time. The content of each table and the content of calculation performed by the calculation unit  210  will be described below. 
     (Hardware Configuration Example) 
     The functions of the hierarchical storage control apparatus  20  can be implemented, for example, by causing a computer to execute a program. 
     That is, the functions of the hierarchical storage control apparatus  20  can be implemented by executing a program corresponding to processing performed by the hierarchical storage control apparatus  20  by using hardware resources such as a CPU and a memory built in a computer. The above program can be recorded on a computer-readable recording medium (portable memory or the like) to be stored or distributed. In addition, the above program can be provided through a network such as the Internet or e-mail. 
       FIG. 4  is a diagram illustrating an example of a hardware configuration of the above computer. The computer illustrated in  FIG. 4  includes a drive device  1000 , an auxiliary storage device  1002 , a memory device  1003 , a CPU  1004 , an interface device  1005 , a display device  1006 , an input device  1007 , etc. connected to each other by a bus B. 
     The program for implementing the processing by the computer is provided, for example, by a recording medium  1001  such as a CD-ROM, a memory card, or the like. When the recording medium  1001  storing the program is set in the drive device  1000 , the program is installed in the auxiliary storage device  1002  from the recording medium  1001  via the drive device  1000 . However, the program does not necessarily need to be installed from the recording medium  1001  and may be downloaded from another computer via the network. The auxiliary storage device  1002  stores the installed program and also stores necessary files, data, etc. 
     When the program is instructed to start, the memory device  1003  reads and stores the program from the auxiliary storage device  1002 . The CPU  1004  implements the functions of the hierarchical storage control apparatus  20  in accordance with the program stored in the memory device  1003 . The interface device  1005  is used as an interface for connecting to a network and functions as input means and output means via the network. The display device  1006  displays a GUI (graphical user interface) or the like in accordance with the program. The input device  157  includes a keyboard, a mouse, buttons, a touch panel, or the like and is used to input various operation instructions. 
     (Description of Tables) 
     Next, the tables stored in the storage unit  220  of the hierarchical storage control apparatus  20  will be described. 
       FIG. 5  illustrates a structure of the data center information table  2210 . As illustrated in  FIG. 5 , the data center information table  2210  stores the unique number, name, and location (address or latitude/longitude) of a data center included in the present hierarchical storage management system, the unit price of the electricity charge of the power supplied to the data center, and the construction cost per rack. Each information item is input manually by an administrator or automatically when the hierarchical storage  40  is newly added to (or eliminated from) the present hierarchical storage management system or when any one of the information items is changed. 
       FIG. 6  illustrates a structure of the storage medium information table  2220 . As illustrated in  FIG. 6 , the storage medium information table  2220  stores the unique number assigned to the storage medium  420  by the hierarchical storage control apparatus  20 , reading time, capacity, power consumption during standby and during reading, lifetime, acquisition price, etc. Each information item is input manually by an administrator or automatically when the storage medium is newly added (or eliminated) or when any one of the information items is changed. 
       FIG. 7( a )  illustrates a structure of the transmission line information table  2230 . As illustrated in  FIG. 7( a ) , the transmission line information table  2230  stores the unique number assigned by the present hierarchical storage management system to an individual transmission line connecting between the data centers  30 , the data center numbers of the data centers located at both ends of the transmission line, and the communication speed of the transmission line. Each information item is input manually by an administrator or automatically when a new transmission line is established or when any one of the information items is changed. The transmission line may be a dedicated line for the operator of the hierarchical storage management system or a public line. 
       FIG. 7( b )  illustrates a structure of the calculation interval table  2240 . As illustrated in  FIG. 7( b ) , the calculation interval table  2240  stores intervals (for example, one year, one month) for the calculation determined by the data center operator or the administrator to be performed periodically. The calculation interval is updated when the administrator performs an input to the hierarchical storage management system. 
       FIG. 7( c )  illustrates a structure of the execution log table  2250 . As illustrated in  FIG. 7( c ) , the execution log table  2250  stores the calculation execution date and time in the past. 
       FIG. 8  illustrates a structure of the operation policy table  2260 . As illustrated in  FIG. 8 , the operation policy table  2260  stores the operation policy of the present hierarchical storage management system. The data center operator or the administrator determines the rank of the delay time, power consumption, and cost, and stores these information items in association with a corresponding policy number. 
       FIG. 9  illustrates a structure of the stored data management table  2270 . As illustrated in  FIG. 9 , the stored data management table  2270  manages all the data stored in the present hierarchical storage management system in cooperation with the management unit  430  of the hierarchical storage  40  in each of the data centers  30 . When new data is stored in the recording medium  420  in the storage unit  410 , a record is added to the stored data management table  2270  to record the data number of the data, data size, number of the storage medium storing the data, the number of reference counts, most frequent reference source area, policy number freely set by the administrator, and the communication speed, power consumption, and cost obtained by the calculation, which will be described below, are recorded. 
     (Processing Operation of Hierarchical Storage Control Apparatus  20 ) 
     Hereinafter, the details of the calculation processing performed by the calculation unit  210  of the hierarchical storage control apparatus  20  will be described with reference to a flowchart in  FIG. 10 . 
     The calculation unit  210  compares the latest calculation execution date and time in the execution log table  2250  with the date and time of the timer  230 , and when the calculation interval stored in the calculation interval table  2240  has elapsed, the calculation unit  210  starts a calculation. In addition, the calculation unit  210  stores the data and time when the calculation is started in the execution log table  2250 . 
     In S 1  (step  1 ) in  FIG. 10 , the calculation unit  210  performs the following processing for each of all the data managed in the stored data management table  2270 : the calculation unit  210  calculates the annual power consumption needed for storing the data by using the following formula (1), calculates the annual cost needed for storing the data by using the following formula (2), and calculates the communication speed from the data center storing the data to the most frequent reference source area by using the following formula (3). Since time needed for reading and transmitting data is used as the communication speed in the present embodiment, the communication speed may be referred to as communication time instead. In addition, while the annual value is used in the present example, a value for a period other than one year may be used. 
         PU   year   =T   read   ×F   read   ×P   read +(8760− T   read   ×F   read )× P   idle    formula (1)
 
     PU year : annual data storage power consumption
 
T read : reading time
 
F read : reference frequency
 
P read : power consumption during reading
 
P idle : power consumption during standby
 
         C   year   =PU   year ×Charge power +(Charge foorprint ×Size data )÷Density storage +(Charge media ×Size data )÷(Capacity media ×Lifetime media )  formula (2)
 
     C year : annual data storage cost
 
PU year : data storage power consumption
 
Charge power : electricity charge
 
Charge foorprint : space cost
 
Size data : data size
 
Density storage : storage medium recording density
 
Charge media : unit price of the storage medium
 
Capacity media : capacity of the storage medium
 
Lifetime media : lifetime of the storage medium
 
         T   DL   =T   read   +T   1   formula (3)
 
     T EL : data download time from the data center to the reference source
 
T read : reading time
 
T 1 : communication speed (communication time) of the NW
 
     In S 2 , the calculation unit  210  stores the annual power consumption, the annual cost, and the communication speed from the data center to the most frequent reference source area, which have been calculated in S 1 , in the stored data management table  2270  per data. 
     In the present example, first, the power consumption, the cost, and the communication speed are calculated for each of all the data, and subsequently, determination, etc. in S 3 , which will be described below, are performed. Alternatively, however, repetitive processing of “calculation, determination, change” (until the operation policy is satisfied) per data may be performed. 
     In S 3 , the calculation unit  210  compares the resultant values (the annual power consumption, the annual storage cost, and the communication speed) calculated in S 1  with values set for the policy number corresponding to the data in the operation policy table  2260  per data and determines whether all the values satisfy the corresponding values of the operation policy. When all the values of all the data satisfy the corresponding values in the respective operation policies, the processing ends. 
     When there is one or more data having the value that does not satisfy the value of the corresponding operation policy, the processing of S 4  through S 8  is performed on each of the one or more data. 
     In S 4 , the data center base and the storage medium corresponding to the data are changed. Alternatively, the data center base may not be changed, and only the storage medium may be changed. How the change is performed is not particularly limited. For example, the change may be made by increasing (or decreasing) the data center number/storage medium number. After the change has been made, the calculation is performed on the assumption that the data is stored in a changed storage medium. 
     The processing of S 4  through S 7  is then repeated until the determination in S 7  (the same determination as in S 4 ) becomes Yes. The content of the calculation in S 5  is the same as that in S 1 . 
     When the determination in S 7  becomes Yes (when the operation policy is satisfied), the calculation unit  210  transfers the data to the storage medium of the data center at that time. The transfer of data from one data center to another data center can be implemented by instructing the management unit  430  of the hierarchical storage  40  in the relevant data center. 
     EXAMPLE 
     Hereinafter, an example will be described as a more specific example.  FIG. 11  illustrates the locations of the data centers in the present example. As illustrated in  FIG. 11 , four data centers (South Kanto, North Kanto, Joshinetsu, Hokkaido) are located in the eastern Japan area. 
       FIG. 12  illustrates a configuration of the hierarchical storage management system of the present example. As illustrated in  FIG. 12 , each data center is provided with the hierarchical storage  40 . A configuration of a storage medium in the individual hierarchical storage  40  is as illustrated in  FIG. 11 . In the present example, the hierarchical storage control apparatus  20  is provided in the South Kanto area. The hierarchical storage control apparatus  20  is connected to each data center via a public network. 
       FIG. 13  illustrates the data center information table  2210  of the present example. As illustrated in  FIG. 13 , the data center information table  2210  stores the name, location, unit price of the electricity charge, and construction cost per rack of each data center. The construction cost per rack is a value obtained by dividing the number of accommodated racks by the total construction cost. 
       FIG. 14  illustrates the storage medium information table  2220  of the present example. As illustrated in  FIG. 14 , the storage medium information table  2220  stores information about the storage accommodated in each data center. 
       FIG. 15( a )  illustrates the transmission line information table  2230  of the present example. The transmission line number in the transmission line information table  2230  in  FIG. 15( a )  corresponds to a number assigned to the individual transmission line in  FIG. 12 . 
     In the present example, with respect to the South Kanto, the South Kanto and Joshinetsu are connected by a dedicated line, and the South Kanto and Hokkaido are also connected by a dedicated line. The South Kanto and the North Kanto are connected via a public network, instead of a dedicated line. Alternatively, the data centers may be directly connected to one another by a dedicated line or may be connected via a public network. 
       FIG. 15( b )  illustrates the calculation interval table  2240  of the present example. In the present example, the hierarchical storage control apparatus  20  performs the calculation and rearranges the stored data at intervals of one month. Thus, the calculation interval stored in the calculation interval table  2240  is set to one month. 
       FIG. 15( c )  illustrates the execution log table  2250  of the present example. As described above, the execution log table  2250  stores the calculation time in the past. In the present example, the calculation is performed on the first of every month. 
       FIG. 16  illustrates the operation policy table  2260  of the present example. The business operator determines a communication speed (communication time) needed for downloading the data, power consumption needed for storing the data, and a cost based on the construction cost, the acquisition price of the storage, the electricity charge, etc. and assigns an operation policy number to each operation policy in the operation policy table  2260 . 
     For example, as an operation policy assuming data for which latency is not allowed, achieving low delay regardless of the power consumption or the cost is set as a condition of policy number “1”. In addition, for example, as an operation policy assuming a large amount of data having a low reference frequency, having the smallest cost is set as a condition of policy number “3”. 
     Hereinafter, an example of the detailed processing performed by the calculation unit  210  of the present example will be described. 
     First, it is assumed that data is uploaded as illustrated in the stored data management table  2270  in  FIG. 17 . That is, the following example case will be considered: data having a data size of 300 GB is stored in the SSD “21” of the North Kanto data center as data number 1, data of 1 TB is stored in the HDD “11” of the South Kanto data center as data number 2, and data of 500 MB is stored in the magnetic tape “71” of Hokkaido data center as data number 3. 
     The users who have uploaded the above data have set policy numbers 5, 4, and 1 to the data number 1, 2, and 3, respectively. In addition, the number of reference counts and the most frequent reference source areas at the time when the first calculation is performed are as illustrated in  FIG. 17 . 
     The calculation described with reference to the flowchart in  FIG. 10  starts on the first day of the following month of the data storage. In the present example, the calculation performed for the data of the data number “2” will be described as an example. 
     The calculation unit  210  calculates the annual power consumption needed for storing the data of the data number “2” by using the formula (1).  FIG. 18  illustrates the content of the calculation. 
     With regard to the data of the data number “2” stored in the storage medium of the storage medium number 11, T read  (a single data reading time (h/time)) is (1 T[B]/200 M[B/s])=3600 based on  FIG. 14 . F read  (annual reference frequency) is 20 times, P read  (power consumption of a single reading of 60 T) is 10 [W], and the total capacity of the storage medium is 60 T. Therefore, T read ×F read ×P read  (annual power consumption needed for reading) is ((1 T[B]/200 M[B/s])/3600)×20×10/60, as illustrated in  FIG. 18 . 
     Further, based on  FIG. 14 , since P idle  (power consumption during standby) is 5 [W], the annual power consumption needed for standby is (8760−(((1 T[B]/200 M[B/s])/3600)×20)×5=60, as illustrated in  FIG. 18 . The sum of the above resultant values is, as illustrated in  FIG. 18, 730 , which is the annual power consumption. 
     Further, the calculation unit  210  calculates the annual cost needed for storing the data of the data number “2” by using the formula (2).  FIG. 19  illustrates the content of the calculation in detail. 
     Since Charge power  (electricity charge) is 20 [yen/Wh], PU year ×Charge power =730×20=14600 [yen]. 
     In the present example, since Charge foorprint  (space cost) is 2,000,000/2, and Density storage  (storage medium recording density) is 60 T, (Charge foorprint ×Size data )÷Density storage =2,000,000/2×1/60=16667 [yen]. 
     Further, since Charge media  (unit price of the storage medium)=5,000,000, Capacity media  (capacity of the storage medium)=60, and Lifetime media  (lifetime of the storage medium)=4, (Charge media ×Size data )÷(Capacity media ×Lifetime media )=5,000,000×1/(60×4)=20833 [yen]. 
     Therefore, by summing up these resultant values, C year =52100 [yen] is obtained. 
     Further, the calculation unit  210  calculates the communication speed (communication time) from the data center storing the data to the most frequent reference source area by using the formula (3).  FIG. 20  illustrates the details. 
     In the present example, Since T read  (reading time)=1 TB/200 MB, and T 1  (communication time of the NW)=0, T DL =5000 S. 
     The calculation unit  210  stores the annual power consumption, the annual cost, and the communication speed from the corresponding data center to the most frequent reference source area, which have been calculated as described above, in the stored data management table  2270 .  FIG. 21  illustrates the portion of the data number 2 in the stored data management table  2270  after the above calculation results have been stored. 
     The calculation unit  210  acquires the communication speed, the power consumption, and the cost corresponding to the policy number “4” set for the data of the data number 2 from the operation policy table  2260 . The calculation unit  210  compares these acquired values with the communication speed, the power consumption, and the cost calculated above. 
     Since the communication speed, the power consumption, and the cost all exceed the threshold values of the policy number “4”, the calculation unit  210  determines that the storage medium HDD “11” currently storing the data does not satisfy the operation policy. Thus, the calculation unit  210  changes the storage medium and performs the calculation, and the calculation is continued until the values are within the range of the policy number “4”. 
     Effects of the Embodiment 
     According to the technique in the present embodiment described above, when certain data is stored in any one of the plurality of data centers, the data center and the type of storage medium can be automatically selected for the data to be stored in accordance with the communication speed between the data centers and the power consumption and the cost needed for storing the data set in advance by the business operator. As a result, the power consumption and the cost can be reduced, and this leads to reductions of the electricity charge and environmental load as well as an improvement in QoS. 
     SUMMARY OF THE EMBODIMENT 
     The present description discloses at least the hierarchical storage management system, the hierarchical storage control apparatus, the hierarchical storage management method, and the program in the following items. 
     (Item 1) 
     A hierarchical storage management system, including: a hierarchical storage that is provided in an individual data center and has at least one storage medium; and a hierarchical storage control apparatus that manages at least one hierarchical storage, wherein the hierarchical storage control apparatus includes a calculation unit that performs processing for obtaining, for individual data managed by the hierarchical storage control apparatus, a storage medium in a data center that satisfies an operation policy by calculating power consumption needed for storing the data, a cost needed for storing the data, and communication time for transferring the data from a data center to a reference source area and by comparing the calculated power consumption, cost, and communication time with the operation policy set for the data. 
     (Item 2) 
     The hierarchical storage management system according to item 1, wherein, when the calculation unit determines that the calculated power consumption, cost, and communication time do not satisfy the operation policy set for the data, the calculation unit changes a storage medium storing the data and performs the processing on an assumption that the data is stored in a changed storage medium. 
     (Item 3) 
     The hierarchical storage management system according to item 1 or 2, wherein the calculation unit calculates power consumption needed for storing the data by calculating a sum of power consumption for data reading from the storage medium storing the data and power consumption during standby, 
     calculates a cost needed for storing the data by calculating a sum of a cost of power consumption of the storage medium, a cost of installing the storage medium, and a cost of acquiring the storage medium, and 
     calculates communication time for transferring the data from a data center to a reference source area based on a reading speed of the storage medium and a communication speed of a transmission line between the data center in which the storage medium is installed and the reference source area. 
     (Item 4) 
     A hierarchical storage management method used in a hierarchical storage management system including: a hierarchical storage that is provided in an individual data center and has at least one storage medium; and a hierarchical storage control apparatus that manages at least one hierarchical storage, 
     wherein the hierarchical storage control apparatus performs processing for obtaining, for individual data managed by the hierarchical storage control apparatus, a storage medium in a data center that satisfies an operation policy by calculating power consumption needed for storing the data, a cost needed for storing the data, and communication time for transferring the data from a data center to a reference source area and by comparing the calculated power consumption, cost, and communication time with the operation policy set for the data. 
     (Item 5) 
     A hierarchical storage control apparatus used in a hierarchical storage management system including: a hierarchical storage that is provided in an individual data center and has at least one storage medium; and a hierarchical storage control apparatus that manages at least one hierarchical storage, 
     wherein the hierarchical storage control apparatus includes a calculation unit that performs processing for obtaining, for individual data managed by the hierarchical storage control apparatus, a storage medium in a data center that satisfies an operation policy by calculating power consumption needed for storing the data, a cost needed for storing the data, and communication time for transferring the data from a data center to a reference source area and by comparing the calculated power consumption, cost, and communication time with the operation policy set for the data. 
     (Item 6) 
     A program that causes a computer to function as the calculation unit in the hierarchical storage control apparatus according to Item 5. 
     While the present embodiment has thus been described, the present invention is not limited to the above specific embodiment, and various variations and modifications may be made without departing from the scope of the present invention. 
     REFERENCE SIGNS LIST 
     
         
           10  Network 
           20  Hierarchical storage control apparatus 
           30  Data center 
           40  Hierarchical storage 
           50  User 
           210  Calculation unit 
           220  Storage unit 
           230  Timer 
           420  Storage medium 
           410  Storage unit 
           430  Management unit 
           2210  Data center information table 
           2220  Storage medium information table 
           2230  Transmission line information table 
           2240  Calculation interval table 
           2250  Execution log table 
           2260  Operation policy table 
           2270  Stored data management table 
           1000  Drive device 
           1001  Recording medium 
           1002  Auxiliary storage device 
           1003  Memory device 
           1004  CPU 
           1005  Interface device 
           1006  Display device 
           1007  Input device