Abstract:
An apparatus connected to first and second storages performs data transfer between the first and second storages for a plurality of times with different data sizes, and measures a transfer time defined as a transfer interval time for data transfer of each of the plurality of times. The apparatus identifies a maximum size data indicating a maximum data size for data transfer between the first and second storages, based on the transfer time and the data size for data transfer of each of the plurality of times. When data transfer is performed between the first and second storages, the apparatus divides transfer target data for the data transfer into plural pieces of divided data, based on the maximum size data, and outputs, for each of the plural pieces of divided data, a data transfer request for requesting the apparatus to perform data transfer between the first and second storages.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2013-106351, filed on May 20, 2013, the entire contents of which are incorporated herein by reference. 
       FIELD 
       [0002]    The embodiments discussed herein are related to apparatus and method for performing data transfer between storages. 
       BACKGROUND 
       [0003]    In recent years, there has been an increase in the amount of data processed by information processing apparatuses, such as a computer. Nowadays, it has become common for an information processing apparatus to process a larger amount of data than before. As a result, a hierarchical storage system, which makes it possible to higher access than before while suppressing data storage cost, has been adopted in many cases. 
         [0004]    In storage, storage cost per unit amount of data tends to increase as an access speed increases. Accordingly, in tiered storage with two kinds of storages having different access speeds, all the data is stored in an inexpensive storage having a lower access speed, and part of data that is thought to be frequently used is stored in an expensive storage having a higher access speed. By using an inexpensive low-speed storage or an expensive high-speed storage depending on circumstances, it becomes possible to perform high speed access while suppressing data storage cost. 
         [0005]    In tiered storage, data transfer is performed between storages as occasion arises. Data transfer between storages is performed by an information processing apparatus capable of accessing two storages between which data transfer is performed. The information processing apparatus performs data transfer between storages by a program that carries out storage tiering. It is possible to roughly divide the data transfer between storages into data transfer for copying data from one storage to the other storage, and data transfer for relocating data from one storage to the other storage. 
         [0006]    A transfer unit for performing data transfer between storages is a data unit, such as a logical unit number (LUN) or a sub-LUN. The amount of data of such data unit is specifically hundreds of giga bytes (GB), for example. In the case of performing data transfer of the above-described amount of data, an information processing apparatus divides data into blocks having a predetermined size, and performs data transfer for each divided data under an operating system (OS) that is running. 
         [0007]      FIG. 1  is a diagram illustrating an example of data transfer executed under the control of an OS. As illustrated in  FIG. 1 , when transfer source data  1 , which is a transfer unit specified as a transfer source, has a certain amount of data or more, the OS divides the transfer source data  1  into a plurality of divided data is each having a predetermined size, and performs data transfer for each divided data  1   a.  Accordingly, the OS causes the information processing apparatus to transmit a data transfer request for performing data transfer between storages to a target storage for each divided data  1   a.  By transmitting a data transfer request for each divided data  1   a,  it is possible to transmit another request (user request) that requests an access to the storage storing the transfer source data  1  until transmission of all the data transfer requests is completed. 
         [0008]    In continuous issuing of requests, such as issuing of a request for each divided data  1   a,  a response from a storage to a previous request is normally waited, and then a next request to be issued is made. However, there is an exception. 
         [0009]    For example, in a storage, such as a hard disk apparatus, the amount of head movement heavily influences an access speed. In such a storage, making the amount of head movement smaller results in an increase in the number of input/output (I/O) requests allowed to be processed per unit time. Accordingly, when a larger number of I/O requests, which are user requests for performing sequential access with small amount of head movement, are issued, or when a requested transmission destination storage has a high load (is busy), an OS gives priority to the issue of such I/O request (transmission (selection)) over the other I/O requests. As a result, a data transfer request to perform data transfer between storages is selected at certain intervals. Hereinafter the certain time period is expressed as “time-out time”. 
         [0010]      FIG. 2  is a diagram illustrating an example of a graph indicating delay time from issue of an I/O request to reception of a response when a sequential access with higher load than usual occurs. The horizontal axis represents time (elapsed time from measurement start; the unit is second), and the vertical axis represents delay time (expressed as “I/O request delay” in  FIG. 2 ; the unit is second). Each point represents a corresponding I/O request. The points representing data transfer requests for data transfer between storages are expressed by being enclosed with circles, respectively, in  FIG. 2 . Thus, all the other points that are not enclosed by a circle represent user requests. 
         [0011]    Normally, an OS separates requests by a priority set for a type of the request, and preferentially selects a request having a higher priority. In the case of selecting a request by priority in that way, a request having a low priority is not selected in a circumstance that includes higher priority requests. Accordingly, it is a common practice that the OS temporarily changes the priority of a request to be selected at certain intervals, namely at time-out time intervals, and selects a low-priority request even in a circumstance that includes higher priority requests. 
         [0012]    As is apparent that a data transfer request has a longer delay time than a user request has, a data transfer request that performs data transfer between storages is handled as a low priority request. Accordingly, a data transfer request that has been issued is selected by elapse of time-out time, and is issued to a storage. As a result, as illustrated in  FIG. 2 , each data transfer request is issued substantially at time-out intervals in sequence. A substantially same delay time for each data transfer request indicates that a delay time of each data transfer request is substantially the same as the time-out time. 
         [0013]      FIG. 3  is a diagram illustrating an example of a relationship between data transfer size and delay time when a high-load sequential access occurs. The horizontal axis represents data transfer size, and the vertical axis represents delay time (expressed as “response” in  FIG. 3 ). Here, the delay time is a time period from when a request of data transfer is made to an OS to when a response indicating the completion of the data transfer is received from a storage. A line  31  represents a relationship between data transfer size and delay time for the case of a user request, and a line  32  represents a relationship between data transfer size and delay time for the case of a data transfer request. 
         [0014]    In data transfer by a user request, as illustrated by the line  31 , delay time for the data transfer becomes exponentially long in accordance with data transfer size. On the other hand, as illustrated in  FIG. 2 , delay time regarding a data transfer request includes time-out time. Accordingly, as illustrated by the line  32 , delay time becomes long in a stepwise manner in accordance with data transfer size. If it is assumed that delay time of one data transfer request is equal to time-out time, delay time becomes time produced by multiplying the number of divisions of transfer source data  1  by time-out time (=the number of divisions×time-out time). 
         [0015]    An access to the transfer source data  1  to be transferred becomes possible when the data transfer is complete. That is to say, an access to the transfer source data  1  is prohibited during a time period in accordance with the number of divisions of the transfer source data  1 . Data transfer between storages is performed in order to move data that is normally used or data having a high possibility of being used to a higher-speed storage. This means that there is a high possibility that a user request for accessing at least part of the transfer source data  1  occurs before the completion of data transfer of the transfer source data  1 . Accordingly, in order to realize efficient data processing, it seems important to allow access to part of data to be transferred before completion of data transfer between storages. 
         [0016]    Related-art techniques have been disclosed in Japanese Laid-open Patent Publication Nos. 2003-216460 and 2011-165164. 
       SUMMARY 
       [0017]    According to an aspect of the invention, an apparatus connected to first and second storages performs data transfer between the first and second storages for a plurality of times with different data sizes, and measures a transfer time defined as a transfer interval time for data transfer of each of the plurality of times. The apparatus identifies a maximum size data indicating a maximum data size for data transfer between the first and second storages, based on the transfer time and the data size for data transfer of each of the plurality of times. When data transfer is performed between the first and second storages, the apparatus divides transfer target data for the data transfer into plural pieces of divided data, based on the maximum size data, and outputs, for each of the plural pieces of divided data, a data transfer request for requesting the apparatus to perform data transfer between the first and second storages. 
         [0018]    The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims. 
         [0019]    It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, as claimed. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0020]      FIG. 1  is an explanatory diagram of data transfer executed under the control of an OS; 
           [0021]      FIG. 2  is a graph indicating an example of delay time from issue of an I/O request to reception of a response when a sequential access with higher load than usual occurs; 
           [0022]      FIG. 3  is an explanatory diagram of a relationship between a data transfer size and delay time when a high-load sequential access occurs; 
           [0023]      FIG. 4  is a diagram illustrating an example of a configuration of a hierarchical storage system built using an information processing apparatus according to an embodiment; 
           [0024]      FIG. 5  is a diagram illustrating an example of variables used for a data-size determination unit to identify a data-size value, according to an embodiment; 
           [0025]      FIG. 6  is a diagram illustrating an example of a method for identifying the data-size value by the data-size determination unit, according to an embodiment; 
           [0026]      FIG. 7  is a diagram illustrating an example of an operational flowchart for data-size determination processing, according to an embodiment; 
           [0027]      FIG. 8  is a diagram illustrating an example of a configuration of the information processing apparatus that is usable as a server, according to an embodiment; and 
           [0028]      FIG. 9  is a diagram illustrating an example of an operational flowchart for data-size determination processing, according to an embodiment. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0029]    In the following, a detailed description is given of embodiments of the present disclosure with reference to the drawings. 
         [0030]      FIG. 4  is a diagram illustrating an example of a configuration of a hierarchical storage system built using an information processing apparatus according to an embodiment. As illustrated in  FIG. 4 , the hierarchical storage system includes a server  40 , which is an information processing apparatus according to the embodiment, a hard disk apparatus (HDD)  50 , which is a low-speed storage, and an solid state drive (SSD)  60 , which is a high-speed storage. 
         [0031]    In  FIG. 4 , as an explanation, only one hard disk apparatus  50  and one SSD  60  are individually illustrated for the sake of convenience. However, in many cases, a plurality of hard disk apparatuses  50  and a plurality of SSDs  60  are provided. Also, tiered storage is realized by employing the hard disk apparatus  50  and the SSD  60  as two kinds of storages having different access speeds. However, the storages to be employed are not limited to this combination. The number of tiers is not limited to two. That is to say, the number of tiers may be three or more. 
         [0032]    In  FIG. 4 , as programs running on the server  40 , only an OS  41 , a transfer setting program  42 , and an automated tiering program  43  are illustrated. 
         [0033]    The OS  41  is a program that actually performs data transfer between the hard disk apparatus  50  and the SSD  60 . The transfer setting program  42  is an application program (hereinafter abbreviated as an “application”) provided for optimization of data transfer. 
         [0034]    The automated tiering program  43  is an application that realizes automated tiering of storages in cooperation with the OS  41 , and controls data transfer between the hard disk apparatus  50  and the SSD  60 . Here, it is assumed that the automated tiering program  43  detects a data access frequency, and performs data transfer for relocation of data in accordance with the detected access frequency. 
         [0035]    Each data  51  in the hard disk apparatus  50  is a transfer unit of data. The data  51  has a size for which the OS  41  performs dividing and transfers a plurality of divided data, and is transferred to the SSD  60  as occasion arises. Out of the pieces of data  51  stored in the SSD  60 , the data  51  to be relocated is transferred from the SSD  60  to the hard disk apparatus  50 . The data transfer is performed under the control of the automated tiering program  43 . 
         [0036]    The OS  41  realizes a data access unit  411 , a data movement unit  412 , a scheduler  413 , and a latency monitoring unit  414  as functions. 
         [0037]    The data access unit  411  has a function of issuing a user request by a request from an application running on the OS  41 . Arrows  4   a  ( 4   a - 1  and  4   a - 2 ) denoted by two dotted lines in  FIG. 4  indicate that a user request is transmitted to the hard disk apparatus  50  or the SSD  60 , and a response is returned to the data access unit  411  by the transmission. 
         [0038]    The data movement unit  412  has a function of realizing data transfer between the hard disk apparatus  50  and the SSD  60 , and issues a data transfer request in order to perform the data transfer. An arrow  4   b  denoted by a solid line in  FIG. 4  indicates a transfer path when data transfer is performed in order to move data  51 - 0  stored in the hard disk apparatus  50  to the SSD  60  through the data movement unit  412 . 
         [0039]    The scheduler  413  has a function of inputting requests issued from the data access unit  411  and the data movement unit  412 , and selects one from the input requests to transmit the selected request to the storage to which the request is to be transmitted. 
         [0040]    A request issued by the data access unit  411  and a request issued by the data movement unit  412  have different priorities. The request issued by the data access unit  411  has a high priority, and the request issued by the data movement unit  412  has a low priority. In a state in which there is a request issued by the data access unit  411 , the scheduler  413  selects a request issued by the data movement unit  412  for each elapse of time-out time. 
         [0041]    The latency monitoring unit  414  has a function added in cooperation with the transfer setting program  42 , and measures transfer time (delay time) that is desired for processing all the data transfer requests issued from the data movement unit  412 . The transfer time is a time period from when a first data transfer request is output to the scheduler  413  to when the data movement unit  412  receives input of a response of the hard disk apparatus  50  with respect to a last data transfer request. Hereinafter, this transfer time is also called “response time”. 
         [0042]    The transfer setting program  42  sets a data size with which one data transfer is to be performed when data transfer (relocation) between storages is performed. A size data  44  illustrated in  FIG. 4  is data indicating the set (stored) data-size value. The size data  44  is set in order to make it possible to perform more efficient data processing while carrying out data transfer efficiently. The information processing apparatus that performs data processing may be the server  40 , but may be an information processing apparatus that receives data from the server  40 . 
         [0043]    In order to allow accessing a part of the transfer unit data  51 , the transfer of which has been completed, the automated tiering program  43  divides the data  51  to be relocated, based on the size data  44 , and performs data transfer for each divided data. It is desirable that the size of divided data (hereinafter expressed as a “divided data size”) matches a size of data that is to be transferred once by the data movement unit  412  (hereinafter expressed as a “maximum transfer size”). This is because if the divided data size does not match the maximum transfer size, it is highly likely that a larger number of data transfer requests are actually issued. 
         [0044]    When the divided data size is less than the maximum transfer size, the following relationship holds: ceil (the size of data  51 /the divided data size) ceil (the size of data  51 /the maximum transfer size), where the “ceil” is a function representing an integer produced by rounding up decimal places of the argument. 
         [0045]    Normally, the maximum transfer size is greatly different from the size of data  51 . Accordingly, unless the difference between the divided data size and the maximum transfer size is very small, the following relationship holds: ceil (the size of data  51 /the divided data size)&gt;ceil (the size of data  51 /the maximum transfer size). Thus, when the divided data size is smaller than the maximum transfer size, the number of data transfer requests to be issued is commonly larger compared with the case of performing data transfer by the maximum transfer size. 
         [0046]    On the other hand, when the divided data size is larger than the maximum transfer size, a plurality of data transfer requests are desired to be issued in order to transfer a piece of data of the divided data size. Accordingly, compared with performing data transfer by the maximum transfer size, the number of data transfer requests to be issued becomes large without exception. 
         [0047]    An increase in the number of data transfer requests to be issued means that data transfer efficiency decreases. With the decrease of the data transfer efficiency, the transfer time desired for data transfer (relocation) of the entire data  51  becomes longer. Also, as the transfer time becomes longer, the possibility of 
         [0048]    transmitting requests to the hard disk apparatus  50  becomes high because of the accessing a part of the data  51  that has not been moved to the SSD  60 . 
         [0049]    Accordingly, a decrease in the data transfer efficiency is not desirable in order to realize more efficient data processing. As a result, in the embodiment, a divided data size that is regarded as identical to a maximum transfer size is set as the data size  44  in order to realize higher data transfer efficiency and more efficient data processing. 
         [0050]    In order to set the data size  44 , as illustrated in  FIG. 4 , the transfer setting program  42  includes a data-size determination unit  421 , and a sequential load generation unit  422  as functions. 
         [0051]    The sequential load generation unit  422  has a function of causing the data access unit  411  to issue a user request in accordance with an instruction from the data-size determination unit  421 . The user request to be issued is a sequential access request that makes a sequential access to an adjacent area in the hard disk included in the hard disk apparatus  50 . The user request is issued in order for the scheduler  413  to select a data transfer request issued from the data movement unit  412  at time-out intervals. 
         [0052]    The data-size determination unit  421  has a function of identifying a divided data-size value to be set as the size data  44 . The data-size determination unit  421  causes the data movement unit  412  to issue a data transfer request having a changed divided data-size value under the circumstances in which the sequential load generation unit  422  causes the data access unit  411  to issue a request for a sequential access. Thereby, the data-size determination unit  421  identifies a divided data-size value to be set as the data size  44  from a relationship between the divided data size and the transfer time measured by the latency monitoring unit  414 . 
         [0053]      FIG. 5  is a diagram illustrating an example of variables used for a data-size determination unit to identify a data-size value, according to an embodiment.  FIG. 6  is a diagram illustrating an example of a method for identifying the data-size value by the data-size determination unit, according to an embodiment. Here, a specific description is given of operation related to setting the data size  44  by the data size determination unit  421  with reference to  FIG. 5  and  FIG. 6 . 
         [0054]    In both of the graphs illustrated in  FIG. 5  and  FIG. 6 , the horizontal axis represents data transfer size, and the vertical axis represents transfer time (expressed as “response” in both  FIG. 5  and  FIG. 6 ). As illustrated in  FIG. 5  and  FIG. 6 , the transfer time changes in a staircase pattern in accordance with the data transfer size. 
         [0055]    In  FIG. 5 , “Tmax”, “Rmin”, “Smin”, and “Sopt” are expressed as an example of variables. In  FIG. 6 , “S” is expressed as an example of a variable. These variables are used as follows. 
         [0056]    “Tmax” is a variable to which maximum time that is permissible as transfer time (hereinafter, expressed as a “maximum permissible transfer time”) is assigned. “Rmin” is a variable to which a minimum transfer time is assigned out of transfer times the latency monitoring unit  414  actually measured. The transfer time measured finally at the time of transferring data of a maximum transfer size or less is assigned to the variable Rmin. 
         [0057]    “Smin” is a variable to which a data-size value set as a minimum divided data-size value in advance is assigned. “Sopt” is a variable to which a value to be set to the data size  44 , that is to say, an optimum divided data size value is assigned. “S” is a variable to which a value expressing the data size of data transferred by the data transfer request issued by the data movement unit  412  is assigned. 
         [0058]    In the embodiment, a value to be assigned to the variable Sopt is identified by focusing attention on the fact that transfer time changes in a staircase pattern in accordance with a data transfer size and the fact that the data-size value is usually a value of a power of 2. Accordingly, in the embodiment, it is assumed that a maximum transfer size value is a power of 2, and two kinds of transfer time, a minimum transfer time and the other transfer time are identified. 
         [0059]    The other transfer time becomes about N times the minimum transfer time (N is an integer more than 1). If it is assumed that a data-size value when the other transfer time has been measured is S, a value to be assigned to the variable Sopt, that is to say, the maximum transfer size value becomes as follows: S/N Sopt&lt;S/N×2. Accordingly, when the maximum transfer size value is a power of 2, the maximum transfer size value becomes a value that is a minimum power of 2 not less than S/N. In order to avoid confusion, hereinafter, it is assumed that the transfer time completely match an integer multiple of time-out time, and variations of the transfer time to be measured are disregarded. 
         [0060]      FIG. 6  illustrates the case where the value of N is 2. In this case, a point  6  in  FIG. 6  indicates that the transfer time measured when the data-size value is S is two times the time-out time. The maximum transfer size value to be assigned to the variable Sopt becomes a value that is a minimum power of 2 existing in the range of S/2≦Sopt&lt;S. 
         [0061]    In order to change the transfer time in a staircase pattern in accordance with the data transfer size, it is requested that data transfer is performed in an environment in which user requests exist all the time. Accordingly, in the embodiment, the sequential load generation unit  422  causes user requests for a sequential access to be issued. 
         [0062]    The server  40  executing the transfer setting program  42  including the data-size determination unit  421  and the sequential load generation unit  422  has a hardware configuration as illustrated in  FIG. 8 , for example. Here, with reference to  FIG. 8 , a specific description is given of an example of a configuration of an information processing apparatus that is allowed to be used as the server  40  in the embodiment. 
         [0063]    As illustrated in  FIG. 8 , the information processing apparatus includes a central processing unit (CPU)  81 , a firmware hub (FWH)  82 , a memory (memory module)  83 , a network interface card (NIC)  84 , a hard disk apparatus (HD)  85 , an interface (I/F) unit  86 , a controller  87 , and a baseboard management controller (BMC)  88 . This configuration is one example of an information processing apparatus used as a server  40 . The configuration of an information processing apparatus that is allowed to be used as an information processing apparatus according to the embodiment is not limited to the configuration illustrated in  FIG. 8 . 
         [0064]    The FWH  82  is a memory that stores a firmware. This firmware is read into the memory  83 , and executed by the CPU  81 . The hard disk apparatus  85  stores various programs including the OS  41  and the transfer setting program  42 . The CPU  81  is configured to read, after completion of starting the firmware, various programs including the OS  41  and the transfer setting program  42  from the hard disk apparatus  85  to the memory  83  through the controller  87  to execute the programs. The communication through the NIC  84  becomes possible by starting the firmware or the OS  41 . 
         [0065]    The I/F unit  86  is configured to communicate with a plurality of storages. It is possible to connect the hard disk apparatus  50  and the SSD  60 , illustrated in  FIG. 4 , with the I/F unit  86 . The communication through the I/F unit  86  becomes possible by starting the firmware, for example. 
         [0066]    The NIC  84  allows communication through a network, such as a local area network (LAN), and so on. The NIC  84  may connect the hard disk apparatus  50  and the SSD  60 , illustrated in  FIG. 4 , to a network through which communication is possible. 
         [0067]    The BMC  88  is a dedicated management apparatus for managing the information processing apparatus. The BMC  88  performs on/off control of the CPU  81 , monitoring of an error that occurs in each component, and so on. 
         [0068]    The OS  41  and the transfer setting program  42  illustrated in  FIG. 4  are read from the hard disk apparatus  85  to the memory  83  through the controller  87  which are executed by the CPU  81 . The CPU  81  accesses the hard disk apparatus  85  through the controller  87  after starting execution of the firmware read from the FWH  82 . Thereby, all the functions provided for each of the OS  41  and the transfer setting program  42  are realized by the CPU  81 , the FWH  82 , the memory  83 , the controller  87 , and the hard disk apparatus  85 , for example. The size data  44  is normally stored in the memory  83 . 
         [0069]    The server  40  as an information processing apparatus according to the embodiment is realized by the CPU  81  executing the OS  41  and the transfer setting program  42 . The server  40  as an information processing apparatus according to the embodiment is realized by the CPU  81  at least executing the OS  41  and the automated tiering program  43 . The server  40  as an information processing apparatus according to the embodiment is configured so that the CPU  81  executes the transfer setting program  42  in addition to the OS  41  and the automated tiering program  43 . 
         [0070]      FIG. 7  is a diagram illustrating an example of an operational flowchart for data-size determination processing, according to an embodiment. The data-size determination processing is processing realized by the CPU  81  executing the transfer setting program  42 . The data-size determination unit  421  is realized by executing the data-size determination processing. The transfer setting program  42  is executed, for example, at starting time or by an instruction of an operator. Next, a detailed description is given of the data-size determination processing with reference to  FIG. 7 . 
         [0071]    The CPU  81  is configured to execute all the programs including the transfer setting program  42  and the OS  41 . Thereby, if it is assumed that the main body for executing the processing is the CPU  81 , the program (including a sub-program here) executed by the CPU  81  becomes indistinct. Accordingly, here, a description is given using names of the functions that are individually included in the OS  41  and the transfer setting program  42 . 
         [0072]    First, the data-size determination unit  421  assigns, to the variable S, a value of the variable Smin, that is to say, a minimum divided data-size value (S 1 ). Next, the data-size determination unit  421  generates user requests for a sequential access that makes the utilization of the hard disk apparatus  50  (expressed as “DISK” in  FIG. 7 ) 100%, through the sequential access load generation unit  422  (S 2 ). After that, the data-size determination unit  421  requests the data movement unit  412  of the OS  41  to transfer data using the value of the variable S as the data-size value, obtains the data transfer time measured by the latency monitoring unit  414 , and assigns the obtained data transfer time to the variable Rmin (S 3 ). 
         [0073]    At this time, the data transfer time measured by the latency monitoring unit  414  is time from when the data movement unit  412  issued a data transfer request to the scheduler  413  to time when a response from the hard disk apparatus  50  to which the data request has been transmitted is received. The data in the hard disk apparatus  50  to be requested for transfer may be any data, but it is requested that an area on the SSD  60  to store the transfer data is an unused area or an area storing needless data. 
         [0074]    The data-size determination unit  421  that has assigned the data transfer time to the variable Rmin updates the value of the variable S (S 4 ). The update is performed by newly assigning a value obtained by the product of the value of the variable Tmax divided by the value of the variable Rmin and the value of the current variable S (=Tmax/Rmin*S) to the variable S. The maximum permissible transfer time indicated by the value assigned to the variable Tmax is set to a very long time period compared with the data transfer time (minimum transfer time) indicated by the value assigned to the variable Rmin. Accordingly, the value that is newly assigned to the variable S becomes a very large value compared with the value of the variable S up to that time. 
         [0075]    After updating the value of the variable S, the data-size determination unit  421  makes a request of data transfer to the data movement unit  412  of the OS  41  with the value of variable S being set to the data-size value, obtains the data transfer time measured by the latency monitoring unit  414 , and assigns the obtained data transfer time to the variable R (S 5 ). Next, the data-size determination unit  421  determines whether the value of the variable R is greater than the value of the variable Rmin (S 6 ). When the value of the variable R is greater than the value of the variable Rmin by a predetermined value or more, that is to say, when the difference between the value of the variable R and the value of the variable Rmin is regarded as one time-out time or more, the determination of S 6  becomes Yes, and the processing proceeds to S 7 . When the value of the variable R is not greater than the value of the variable Rmin by a predetermined value or more, the determination of S 6  becomes No, and the processing returns to S 4 . 
         [0076]    In S 7 , the data-size determination unit  421  assigns a minimum power of 2 which is greater than the value of the variable R divided by the value of the variable Rmin to the variable Sopt, and stores the value of the variable Sopt as the size data  44 . After storing the value, the data-size determination unit  421  instructs the sequential load generation unit  422  to stop operation of causing user requests for a sequential access to be issued (S 8 ). After that, the data-size determination processing is terminated. By the termination of the data-size determination processing, the data-size determination unit  421  is stopped. 
         [0077]    As described above, when the maximum transfer size value is a power of two, it is possible to identify the maximum transfer size value properly by measuring the data transfer time two times. Accordingly, compared with a method for identifying a maximum transfer size value by changing the data-size value (the value of the variable S) in sequence, it is possible to identify the maximum transfer size value significantly promptly. 
         [0078]    The automated tiering program  43  performs data transfer between the hard disk apparatus  50  and the SSD  60  with reference to the size data  44  stored by the execution of the data-size determination processing. The automated tiering program  43  divides the data  51  to be transferred, which is stored in the hard disk apparatus  50  or the SSD  60 , by the data-size value indicated by the size data  44 , and instructs the OS  41  to perform data transfer for each divided data. Thereby, the data  51  to be transferred is subjected to data transfer in which access to only a part of the data  51  is prohibited. 
       Another Embodiment 
       [0079]    In the above-described embodiment, the data-size value to be the maximum transfer size value is identified by assuming that the maximum transfer size value by which the OS  41  performs data transfer is a power of two. However, it is thought that the maximum transfer size value might not be a power of two. In the other embodiment, the data-size value that is considered to be the maximum transfer size value is identified by assuming that the maximum transfer size value is not a power of two. 
         [0080]    The configuration of the server (information processing apparatus) in the other embodiment may be the same as that in the above-described embodiment. The program to be executed is basically the same as that of the above-described embodiment. Thus, a description is given of only parts that are different from the above-described embodiment using the symbols of the above-described embodiment. 
         [0081]    In the other embodiment, the data-size determination unit  421  is different from that of the above-described embodiment. The data-size determination unit  421  in the other embodiment is realized by executing the data-size determination processing illustrated in  FIG. 9 . Thus, a detailed description is given of the data-size determination processing in the other embodiment with reference to  FIG. 9 . Here, a main body that executes processing is assumed to be functions included in the OS  41  and the transfer setting program  42 . 
         [0082]    First, the data-size determination unit  421  measures the data transfer time to be assigned to the value of the variable Rmin, and performs Rmin measurement processing for assigning the value indicating the measured data transfer time to the variable Rmin (S 11 ). For the Rmin measurement processing, for example, the processing of S 1  to S 3  in  FIG. 7  may be performed. 
         [0083]    Next, the data-size determination unit  421  assigns the value of the variable Sset to the variable S (S 12 ). The value of the variable Sset is a value to be at least two times the maximum transfer size value or more. For example, it is possible to calculate the value in the same method as that of S 4  in  FIG. 7 . After that, the data-size determination unit  421  requests the data movement unit  412  of the OS  41  to perform data transfer with the value of the variable S being set to the data-size value, obtains the data transfer time measured by the latency monitoring unit  414 , and assigns the obtained data transfer time to the variable T (S 13 ). 
         [0084]    The data-size determination unit  421 , which has assigned the data transfer time to the variable T, assigns the quotient value when the value of the variable T is divided by the value of the variable Rmin to the variable N (S 14 ). Next, the data-size determination unit  421  assigns a division result (=S/N) produced by dividing the value of the variable S by the value of the variable N to the variable Smin, and assigns two times the division result value to the variable Smax (S 15 ). 
         [0085]    The data-size determination unit  421 , which has assigned values to the variables Smin and Smax, respectively, assigns the product of the division result obtained by dividing the value until that moment by the value of the variable N and a predetermined value α to the variable S (=(S/N)·α). The predetermined value α is a value set in order to calculate the data-size value for confirming the data transfer time, within the range between the value of the variable Smin and the value of the variable Smax. Accordingly, the predetermined value α has a relationship as follows: 1&lt;α&lt;2. The data-size determination unit  421 , which has updated the value of the variable S, makes a request of data transfer to the data movement unit  412  of the OS  41  with the data-size value being set to the value of the updated variable S, obtains the data transfer time measured by the latency monitoring unit  414 , and assigns the obtained data transfer time to the variable T (S 17 ). 
         [0086]    Next, the data-size determination unit  421  determines whether the value of the variable T is equal to the value of the variable Rmin (S 18 ). When the value of the variable T is not equal to the value of the variable Rmin, that is to say, when the value of the variable T is greater than the value of the variable Rmin, the determination of S 18  becomes No, and the processing proceeds to S 20 . when the value of the variable T is equal to the value of the variable Rmin, the determination of S 18  becomes Yes, and the processing proceeds to S 19 . 
         [0087]    In S 19 , the data-size determination unit  421  assigns the value of the variable S to the variable Smin. After that, the processing proceeds to S 21 . On the other hand, in S 20 , the data-size determination unit  421  assigns the value of the variable S to the variable Smax. After that, the processing proceeds to S 21 . 
         [0088]    In S 21 , the data-size determination unit  421  determines whether the result when the value of the variable Smin is subtracted from the value of the variable Smax is less than the result when the value of the variable Smin is multiplied by a predetermined value d. The predetermined value d is a value set in order to determine whether the subtraction result is sufficiently small or not. Thus, when the subtraction result is regarded as a sufficiently small value, the determination of S 21  becomes Yes, and the processing proceeds to S 22 . When the subtraction result is not regarded as a sufficiently small value, the determination of S 21  becomes No, and the processing returns to S 14 . 
         [0089]    In S 22 , the data-size determination unit  421  assigns the value of the variable S to the variable Sopt, and stores the value of the variable Sopt as the size data  44 . After storing the value, the data-size determination unit  421  instructs the sequential load generation unit  422  to stop operation that causes user requests for a sequential access to be issued (S 23 ). After that, the data-size determination processing is terminated. By the termination of the data-size determination processing, the data-size determination unit  421  stops. 
         [0090]    When the processing returns to S 14  because the determination of S 21  is No, another value is assigned to the variable S in S 16 . Thereby, the processing loop from S 14  to S 21  is repeatedly executed while changing the value of the variable S until when the determination of S 21  becomes Yes. A method for identifying a maximum transfer size value in the case where the maximum transfer size value is not assumed to be a power of two is not limited to the above-described method. Another method may be employed. 
         [0091]    In this regard, in each of the above-described embodiments, the server  40  as an information processing apparatus may be an information processing apparatus other than an information processing apparatus that performs data transfer between storages. That is to say, the information processing apparatus may not perform data transfer between storages. 
         [0092]    All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiments of the present invention have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.