Storage system and capacity allocation method therefor

A storage system connected to a terminal, the computer system includes: a plurality of drive devices that respectively drive a plurality of physical disks each having a physical storage area; a RAID configuration unit that configures a plurality of RAID groups by grouping two or more of the plurality of physical disks; a logical disk creation unit that creates, for the terminal through the RAID group, a logical disk having a logical storage area associated with the physical storage area; a memory for storing a RAID group control table showing, for each the RAID group, (i) a free capacity that is the amount of physical storage area remaining in the RAID group to be able to be associated with the logical disk and (ii) a power status of the RAID group; a receiver that receives a request for creating a new logical disk; and an area allocation unit that allocates to the new logical disk the physical storage area remaining in the RAID group selected by giving priority to a RAID group in a powered state over a RAID group in a non-powered state with reference to the RAID group control table.

CROSS-REFERENCES TO RELATED APPLICATION

This application relates to and claims priority from Japanese Patent Application No. P2005-348690, filed on Dec. 2, 2005, the entire disclosure of which is incorporated herein by reference.

BACKGROUND

1. Technical Field

The present invention relates to a computer system, and more particularly, to a control method for reducing the amount of power consumed by such device by managing the storage capacity thereof.

2. Related Art

In recent years, as information technology has advanced, the amount of information used by companies, government agencies and individuals has increased dramatically. This trend has led to a demand for storage systems with much higher storage capacities.

At present, storage systems with a plurality of hard disk drives installed therein are used as storage systems to store such information, but because these hard disk drives consume a large amount of electricity, demand continues to exist for hard disk drives that consume less power.

Accordingly, a technology that partially shuts off power to hard disk drives that are not being used by the storage system has been investigated as one method by which to reduce power consumption (see JP-A-8-190762 (Patent Document 1), for example).

Furthermore, there are situations in which the original storage capacity of the storage system bought by the user is insufficient, and additional hard disk drives must be purchased. To address this situation, an on-demand service has been developed in which extra hard disk drives are included in a storage system and the user is charged for only the storage capacity used (see JP-A-2002-190762 (Patent Document 2), for example). In Patent Document 2, a technology is disclosed in which, in order to achieve a rapid increase in storage capacity, the provider of the on-demand service (i) installs and delivers to the customer both hard disk drives actually purchased by the customer and hard disk drives that were not purchased by the customer, and (ii) when the customer executes a contract to increase the storage capacity, assigns one or more of the non-purchased disk drives for use by the customer.

Incidentally, according to Patent Document 1, the power supply to hard disks that are not being used by the customer is cut off. When the customer executes a contract to increase the storage capacity, power is connected to the hard disk drives to which the power had been cut off. Here, in Patent Document 2, when additional storage capacity is to be allocated to the user, one or more logical disks are created from the previously non-powered physical disks and are assigned to the user.

SUMMARY

In the technologies described in Patent Documents 1 and 2, where the storage capacity allocated to the user is increased, the amount of power consumption increases in tandem with the expansion in storage capacity, but insufficient attention has been paid to reducing this power consumption.

An advantage of some aspects of the invention realizes a storage system that employs ‘storage on demand’ technology and can limit power consumption to such as the minimum necessary amount.

A storage system according to an aspect of the invention has hard disk drives that each drives a hard disk comprising a physical disk, and when a logical disk comprising a logical storage area is created via association with one of these physical disks, a physical disk that is in a powered state is allocated to the new logical disk with a higher priority than a physical disk in a non-powered state.

Because powered disks are given priority in allocation to logical disks, an increase in the power consumption of the storage system that implements an on-demand service can be minimized.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the invention are described below with reference to the drawings. In this Specification, ‘0x’ at the beginning of a text string indicates that it is a hexadecimal value: ‘0x12’, for example, indicates the value of ‘18’ expressed in the decimal system.

First Embodiment

FIG. 1is a block diagram showing the hardware configuration of a computer system of a first embodiment. This computer system comprises a plurality of host computers100, a storage system101and a control terminal102used by an administrator to operate the storage system101. The storage system101comprises a plurality of host interfaces block103that controls communication with the host computer100, a management interface114that controls communication with the control terminal102, a control processor104that controls the storage system as a whole, a system memory105that stores control programs executed by the control processor104to control the storage system, hard disk drives106that store data, a disk interface block107that carries out control of the hard disk drives106and communication with the hard disk drives106, and a system bus108that connects the host interface block103, control processor104, disk interface block107and management interface114one another.

Each hard disk drive106is managed in units of storage areas having a certain fixed size. That is, a control program109recognizes a hard disk drive106as a collection of units of this fixed size. These fixed-size units are termed ‘tracks’ in this Specification. In this example described in connection with this embodiment, one track has a size of 256 KB. Furthermore, the storage system of this embodiment is configured such that it may employ RAID technology.

Various control information used by the control processor104is stored in the system memory105. The control program109is a program executed by the control processor104. The control processor104controls the storage system101by executing a control program110. The control program110is normally stored in a non-volatile medium (not shown) such as a flash memory. The control program110is transferred to the system memory105immediately after the power to the storage system101is turned ON and executed by the control processor104. The control program110may alternatively be stored on a hard disk drive106instead of in the non-volatile memory described above. The control information used by the control processor104(synonymous with the control program109) includes a RAID group control table110that stores RAID group information possessed by the storage system101, a physical disk control table111that contains information pertaining to individual hard disk drives106(identical to physical disks), a logical disk control table112that contains information pertaining to the logical disks (not shown) used by the host computer100, and a user management table113that contains information pertaining to the logical disks allocated to individual users.

The above control program includes a RAID configuration module that configures at least one RAID group comprising two or more of the above-described physical volumes that are grouped using RAID technology, a power switching module that switches the power supply to the various hard disk drives between a powered and non-powered state, a logical disk creation module that creates a logical disk associated with a prescribed unit of a physical disk, and an area allocation module that, when a new logical disk is to be created, gives priority in selection and allocation to this new logical disk to a physical disk that is in a powered state over a physical disk that is in a non-powered state. These function modules are realized via execution by the control processor. The above function modules may be provided via software as described above or via hardware such as a CPU or other LSI, or may be realized via a combination of hardware and software.

In this embodiment, a host computer100is a computer that includes, in addition to a CPU, ROM, RAM, HDD and the like, such hardware as an interface by which information is exchanged with the user of a host computer100and an interface by which data is exchanged with the storage system101. An OS and various application programs are installed on each host computer100. Communication between the storage system101and a host computer100may be carried out using any of the methods of SCSI (Small Computer System Interface) incorporating Fibre Channel standards, iSCSI, Gigabit Ethernet, Mainframe Serial Channel or Mainframe Fibre Channel.

The control terminal102of this embodiment is a computer that includes, in addition to a CPU, ROM, RAM, HDD and the like, such hardware as an interface by which information is exchanged with the administrator of the storage system101and an interface by which data is exchanged with the storage system101. An OS and various application programs are installed on the control terminal102.

In this embodiment, a storage system101having one control processor104is used as an example, but a plurality of control processors104may be used. In this case, the information in the system memory105is located on a storage medium that can be referenced and modified by any of the plurality of control processors104.

The RAID group control table110will now be described usingFIG. 2.FIG. 2is an explanatory drawing of the RAID group control table110.

A RAID group is a collection of a plurality of hard disk drives106. The control processor104distributes and stores data within the RAID group. For example, in the case of RAID-5, a hard disk drive106that stores parity information exists within the RAID group, while in the case of RAID-1, the same data is stored on two different hard disk drives106in the RAID group. The RAID group number column200is a column that stores the identifier of each RAID group. The RAID level column201is a column that stores the RAID level of each RAID group. The start track number column202stores the smallest track number value for each of the hard disk drives106belonging to a RAID group.

The control processor104treats the hard disk drives106as collections of tracks, as described above. Each track on a hard disk drive106is assigned a unique identifier.

In this embodiment, an example will be described in which the track numbers of the hard disk drives106belonging to the same RAID group are continuous. However, this embodiment may naturally be utilized even in a case where the track numbers of the hard disk drives106belonging to the same RAID group are not continuous.

The total capacity column203is a column that stores the capacity of each RAID group in units of track. Here, where the RAID group has a RAID-5 or a RAID-1 configuration, the total area of the hard disk drives106is not necessarily available to the user. Therefore, the total capacity available to the user is recorded in the total capacity column203. The free capacity column204is a column that, where a logical disk has been created from an individual RAID group, stores the free usable capacity of the logical disk in terms of the number of tracks.

The power status column205is a column that stores the power status of each RAID group. The powering ON or OFF of hard disk drives106is carried out globally for each RAID group. The running status column206stores the running status of each RAID group. The running status indicates whether the RAID group is operating normally or a failure has occurred. Here, a failure state means that a hard disk drive106has not issued a response to a command from the control program109or that a failure detection circuit (not shown) installed in a hard disk drive106has detected a failure and reported the failure to the control program109.

The row207of the RAID group control table110stores the RAID group information for the RAID group number 0x00000000. In the discussion below, this RAID group will be abbreviated as ‘RAID group 0x00000000’. The RAID level of the RAID group 0x00000000 is RAID-5, and the start track number is 0x00000000. Furthermore, the total capacity is 0xf0000, and the free capacity is 0xd0000. The power status is ON, indicating that the RAID group is in a powered state. The running status is NORMAL, indicating that the RAID group is operating normally. The same situation is indicated in rows208,209.

FIG. 3shows the physical disk control table111. The control processor104writes to the physical disk control table111information regarding each individual physical disk (hard disk drive106). The RAID group number column300indicates the RAID group number that corresponds to a RAID group number shown in the column200ofFIG. 2above and to which a given hard disk drive106belongs. The physical disk number column301is a column used by the control processor104to indicate the identifier allocated to each individual physical disk (hard disk drive106). The track capacity column302is a column used by the control processor104to indicate the capacity per track of each individual hard disk drive106.

The total tracks column303is a column used by the control processor104to indicate the total number of tracks included in a given hard disk drive106. When evaluated together with the track capacity column, the capacity of a hard disk drive106can be determined based on the number of tracks. The power status column304is a column used by the control processor104to indicate the power status of each individual hard disk drive106. The running status column305is a column used by the control processor104to indicate the running status of each individual hard disk drive106.

The row306indicates information regarding the physical disk having a physical disk number 0x00000000. This physical disk will be referred to as ‘physical disk 0x00000000’ below. Its track capacity is 256 KB, and its total number of tracks is 0x50000. Its power status is ‘ON’, indicating that the physical disk is in a powered state. Its running status is ‘NORMAL’, indicating that the physical disk is operating normally. The same is true for rows307-310.

FIG. 4is an explanatory drawing of the logical disk control table112. A logical disk is a collection of tracks extracted by the control processor104from one or more hard disk drives106. The control processor104responds to the host computers'100I/O (Input/Output) commands as if this collection of tracks were a single disk. For example, a logical disk is equivalent to an LU (logical unit) in SCSI terminology. The logical disk number column400is a column used by the control processor104to indicate the identifier allocated to each individual logical disk. The RAID group number column401is a column that indicates the identifier for each RAID group comprising the tracks extracted when the control processor104creates a given logical disk. The logical track number column402indicates the track number of each logical disk, and the start track number column403indicates the number of the physical first track of the actually allocated area within the RAID group. The control processor104can manage the association between a logical disk and the tracks on the physical disks via the logical disk number and start track number. The total capacity column404contains the capacities set by the control processor104for each individual logical disk. The total tracks column405expresses the capacity of each individual logical disk in terms of the number of tracks. Line406shows the information pertaining to a logical disk to which the logical disk number 0x00000000 is allocated (hereinafter referred to as the ‘logical disk 0x00000000’). The logical disk 0x00000000 is created using the tracks of the RAID group 0x00000000, and has a logical disk number of 0x00000000, a start track number of 0x00000000, a total capacity of 16 GB, and 0x00010000 total tracks, as shown in line406. In other words, it is shown that the control processor104allocated the tracks from track number 0x00000000 to track number 0x00010000 to the area of the logical disk 0x00000000 beginning with track number 0x00000000. The same situation is shown in lines407-409. The logical disk 0x00000002 shown in rows408and409comprises tracks extracted from two different RAID groups. In other words, a logical disk can comprise tracks from a plurality of RAID groups.

FIG. 5is an explanatory drawing of the user management table113. The user identifier column400is a column in which the control processor104registers the identifier for the user to which each logical disk is allocated. In general, the user uses a host computer100and the host computer100uses a logical disk or disks. Therefore, the user identifier is synonymous with the identifier of the host computer100. In this embodiment, the identifier of the host computer100is employed as the user identifier. The identifier of the host computer100may comprise a WWN (World-Wide Name) under the Fibre Channel standard, a MAC (Media Access Control) address under the IEEE 802.3 standard or the like, but any identifier that can specify a host computer may be used. The logical disk number in use column501is a column in which the control processor104registers the number of each logical disk allocated to a user (here, a host computer). The capacity column502is a column in which the control processor104registers the capacities of the respective logical disks. The total capacity column503is a column in which the control processor104registers the total capacity of the logical disks allocated to a user (here, a host computer).

For example, row504shows that the logical disks 0x00000000 and 0x00000000 are allocated to the host computer having the identifier 0x0000, the capacity of the logical disk 0x00000000 is 16 GB, the capacity of the logical disk 0x00000001 is 16 GB, and the total capacity is 32 GB. Row505shows the situation regarding the logical disk allocated to the host computer having the identifier 0x0001.

FIG. 6shows a flow chart of the sequence of operations executed when a host computer100issues an I/O command to the storage system101. The storage system101receives the I/O command issued by the host computer100(step601) and executes the command (step602). Once the command is executed, the storage system101reports the result of the command's execution to the host computer100(step603) and ends processing.

FIG. 7is a flow chart of the processing executed when a read or write command is issued by a host computer100to the storage system101. The control processor104of the storage system101extracts the number of the logical disk comprising the target of the command from the received I/O command.

FIG. 17shows the format of the disk I/O commands issued by the host computers100. The disk I/O command1701comprises a logical disk number1702comprising the I/O target, a command code1703that expresses the I/O command in terms of a numerical value, a logical track number1704indicating the logical track to be accessed, and a number of tracks1704that expresses in terms of the number of tracks the data size of the data to be input or output. The control processor104extracts the logical disk number1702. The control processor104specifies the RAID group number corresponding to the above logical disk number with reference to the logical disk control table112(step701).

Next, the control processor104extracts the target logical track number contained in the received I/O command. The control processor104specifies the RAID group track number corresponding to the above logical track number from the RAID group number and the start track number in the logical disk control table112(step702).

Specifically, the control program refers to the logical disk number entries400inFIG. 4and specifies the corresponding RAID group. The track number in the RAID group corresponding to the numerical value of the entry in the logical track number402is stored as the entry in the start track number403. As a result, the control program109can determine the track number in the RAID group corresponding to the logical track number comprising the target of the command.

The control processor104specifies the physical disk track number based on a preset rule regarding the allocation of track numbers within the RAID groups stored in the storage system and the RAID group track number specified in step702. This track number allocation rule is control rule that operates to allocate a track number on a physical disk compatible with the RAID level. For example, in RAID-5 level, physical disk track numbers are associated with RAID group track numbers according to a rule called striping. Specifically, the RAID group track number 0x00000000 is associated with the track number 0x00000000 of the physical disk 0x00000000, and the RAID group track number 0x00000001 is assigned to the track number 0x00000000 of the physical disk 0x00000001. However, the above rule may naturally be modified appropriately based on the RAID level.

The control processor104accesses the physical disk track determined according to the above discussion (step704). Here, ‘access’ refers to the reading or writing of data to or from the physical disk.

In this way, the control processor104converts the track number to be accessed between the logical disk and the physical disk and executes the I/O command.

FIG. 8is a flow chart showing the processing performed during generation of a logical disk where a user request to increase the capacity of an existing logical disk has been issued. According to this flow chart, because when increasing the capacity of a logical disk the control processor104gives priority in the allocation of tracks to unallocated tracks in a powered RAID group and enables the use of these tracks, the increase in power consumption of the storage system as a whole can be minimized.

The flow chart described below is implemented via execution of a control program by the control processor104.

First, the user operates the control terminal102and inputs a requested capacity X comprising the amount of increase in logical disk capacity (step801). The control processor104receives this requested capacity from the control terminal102.

Next, the control processor104checks the free capacity of each RAID group with reference to the RAID group control table10(step802), and selects the RAID group having the largest free capacity among the powered RAID groups (step803).

The control processor104then compares the requested capacity X and the free capacity of the selected RAID group (step804). If the free capacity is larger than X, the control processor104proceeds to step805. If the free capacity is smaller than X, the control processor104advances to step806.

In step805, the control processor104extracts tracks corresponding to the logical disk capacity X from the selected RAID group and creates a new logical disk. Here, when the above tracks are extracted, it is necessary to know the start track numbers of the unused (unallocated) tracks in the powered-state RAID groups; the used tracks in each RAID group can be learned by referring to the RAID group control table110. Specifically, the number obtained by adding the value of the entry in the total capacity203to the value of the entry in the start track number202is the maximum possible value for the used track number. Therefore, the value obtained by adding 1 to this value is recognized as the start track number for the unused area.

In step806, all of the unused tracks in the selected powered RAID group are allocated to the logical disk.

The control processor104then checks, with reference to the RAID group control table110, whether powered RAID groups other than the selected RAID group exist or not(step807). If powered RAID groups other than the selected RAID group do exist, the powered RAID group having the largest free capacity is selected (step808).

If the free capacity of the powered RAID group selected in step808is larger than the capacity X minus the capacity already allocated (step810), a prescribed number of tracks are allocated from the unused tracks in the selected RAID group to the logical disk (step811).

If the free capacity of the RAID group selected in step808is smaller than the capacity X minus the capacity already allocated, the control processor104returns to step806and the operations of steps809to811are repeated until all of the requested capacity X is allocated.

If a powered RAID group other than the selected RAID group does not exist, tracks having a capacity equal to ‘X minus the capacity allocated in step806’ are extracted from a non-powered RAID group and allocated to the logical disk (step809). The method for selecting from among the non-powered RAID groups a RAID group from which the tracks are to be extracted will now be described with reference toFIG. 9.

FIG. 9shows a detailed flow chart of step809. In this processing, the storage system101supplies power to a non-powered RAID group, enabling the previously non-powered RAID group to be used by the host computer100.

First, the capacity Y to be allocated from a non-powered RAID group to the logical disk is established by the control processor104. Y is an amount calculated in step804by subtracting the free capacity of the selected RAID group from the capacity X (step901).

The control processor104then checks the free capacity of each non-powered RAID group with reference to the RAID group control table110(step902) and selects the RAID group having the largest free capacity from among the non-powered RAID groups (step903).

The free capacity Y is then compared with the free capacity of the RAID group selected in step903(step904). If the free capacity of the selected RAID group is larger than Y, the control processor104proceeds to step905. If the free capacity of the selected RAID group is smaller than Y, the control processor104advances to step906.

In step905, the tracks of the selected RAID group are allocated to the logical disk.

In step906, all of the free capacity of the selected RAID group is allocated to the logical disk. The RAID group having the largest free capacity is then selected from among the non-powered RAID groups (step907).

The control processor104then compares the free capacity of the selected RAID group with the capacity obtained by subtracting the already allocated capacity from Y. If the free capacity of the selected RAID group is larger, the control processor104advances to step909. If the free capacity of the selected RAID group is smaller, the control processor104proceeds to step908.

In step909, the free capacity of the RAID group selected in step907is allocated to the logical disk.

According to the flow chart ofFIG. 9, priority in track allocation to the logical disk is given to the non-powered RAID group(s) having the largest free capacity. This enables the storage system101to restrict the number of powered RAID groups, i.e., the number of powered hard disk drives106, in use to the smallest possible number. As a result, the increase in power consumed by the storage system101can be minimized.

Incidentally, the flow chart ofFIG. 8describes a process in which the control processor104selects the RAID groups having the largest free capacity from among the powered RAID groups and then allocates them to the logical disk in the order of the size of their free capacities. However, where a plurality of powered RAID groups exists, the number of powered RAID groups does hot change regardless of the sequence in which the free capacities of the powered RAID groups are allocated to the logical disk.

Therefore, in this case, it does not matter which RAID groups are selected. The processing in this case can be executed by modifying the processing carried out in steps803and808inFIG. 8from selecting the largest free-capacity RAID group to selecting any RAID group from among the plurality of RAID groups having free capacity.

The flow chart of the processing executed in this case is shown inFIG. 10.

First, the user operates the control terminal102and inputs the requested capacity X comprising the logical disk storage amount to be newly created (step1001). The control processor104receives this requested capacity from the control terminal102.

The control processor104then checks the free capacity of each RAID group with reference to the RAID group control table110(step1002) and selects from among the powered RAID groups a RAID group that does not have a free capacity of ‘0’ (step1003). In does not matter how this RAID group is selected during this RAID group selection. In this embodiment, the RAID group having the smallest RAID group number is selected.

The control processor104then compares the free capacity of the selected RAID group with the requested capacity X (step1004). If the free capacity is larger than X, the control processor104proceeds to step1005. If the free capacity is smaller than X, the control processor104advances to step1006.

In step1005, the tracks corresponding to the logical disk capacity amount X are extracted from the selected RAID group and a new logical disk is created.

In step1006, all of the unused tracks in the selected powered RAID group are allocated to this logical disk.

The control processor104then checks, with reference to the RAID group control table110(step1007), whether or not one or more powered RAID groups other than the selected RAID group exist.

If one or more different powered RAID groups exist, a RAID group whose free capacity is not ‘0’ is selected from among the powered RAID groups (step1008).

If the free capacity of the powered RAID group selected in step1008is larger than the capacity obtained by subtracting the already allocated capacity from the capacity X (step1010), a prescribed number of tracks is allocated to the logical disk from the unused tracks belonging to the selected RAID group (step1011).

If the free capacity of the RAID group selected in step1008is smaller than the capacity obtained by subtracting the already allocated capacity from the capacity X, the control processor104returns to step1006and repeats the operations up to and including step1009or step1011until all of the requested capacity X is allocated.

If any powered RAID group does not exist, the number of tracks equivalent to the capacity calculated as ‘X minus the capacity allocated in step1006’ is extracted from a non-powered RAID group and allocated to the logical disk (step1009). In this case, the RAID group having the largest free capacity is selected from among the non-powered RAID groups.

Where the control processor104is to allocate capacity to the logical disk from a powered RAID group, any RAID group may be selected from among the powered RAID groups. However, where the control processor104is to allocate capacity to the logical disk from a non-powered RAID group, priority in selection must be given to the RAID group having the largest free capacity. Otherwise, the increase in power consumption cannot be minimized.

FIG. 11is a schematic drawing of the screen of the control terminal102that is operated by the administrator of the storage system101to allocate capacity. The screen1100is the screen of the control terminal. The user control screen1101is displayed on the screen1100. The user identifier column1102is a column in which user identifiers are displayed and entered. Here, the same information contained in the user identifier column500of the user control table113is entered and displayed. The logical disk column113is a column in which the logical disk number(s) allocated to each user are displayed and entered. Here, the same information contained in the logical disk number column501of the user management table113is entered and displayed. The logical disk capacity column1104is a column in which the capacity of each logical disk is displayed and entered. Here, the same information contained in the capacity column502of the user management table113is entered and displayed. The allocated capacity column1105is a column in which the total capacity of the logical disks allocated to each user is displayed. Here, the same information contained in the total capacity column503of the user management table113is displayed. The columns1106,1107contain information regarding each user. The system free capacity window1108displays the usable free capacity available on the installed hard disk drives106. A logical disk cannot be created if the resulting capacity would exceed the capacity of the installed hard disk drives106. As a result, the control terminal102displays the system free capacity to the user to prevent the user from making configuration settings that cannot be implemented. The administrator can allocate capacity to each user using the control terminal shown inFIG. 11.

Second Embodiment

In the first embodiment, it is assumed that when a logical disk is allocated to a user, the user starts off using the total capacity of that logical disk. In other words, it is assumed that the physical disk(s) corresponding to the logical disk allocated to the user are powered.

However, it does not necessarily mean that the user who is allocated a logical disk immediately begin using the entire capacity of the physical disk(s) corresponding to the allocated logical disk. It is expected that actual usage will resemble the situation shown inFIG. 12.

FIG. 12shows the changes in the capacity of the storage system used by the user over time. The vertical axis1200represents the storage capacity used by the user, while the horizontal axis1201represents time. The stepped line1202inFIG. 12represents the capacity of the logical disk allocated to the user. The curved line1203represents, out of the total capacity allocated to the user, the actually used capacity on the physical disk(s) on which data is actually stored.

InFIG. 12, the user initially uses approximately half of the capacity C1, but the data used gradually increases such that by time T1204, almost all of the capacity C1is being used. Accordingly, the usable capacity is increased at time T1204(at the point where the curved line crosses the broken line) to a usable capacity of C2.

In this case, a method may be envisioned in which not all of the usable capacity C2is allocated to the user as a logical disk, but instead the usable capacity is increased incrementally in accordance with the status of use by the user.

According to the above method, the amount of the physical disk capacity necessary is used, and because fewer physical disks are necessary to create the logical disk, the number of physical disks that receive power can be minimized. This concept is described below with reference to the drawings.

FIG. 13is a block diagram showing the functional internal configuration of the storage system101. In the computer system of the second embodiment, allocation of physical storage areas in response to logical disk modifications is carried out incrementally in accordance with the amount of logical storage space used by each host computer100. The computer system of the second embodiment is identical to the computer system of the first embodiment except that the contents of the logical disk control table1300and user management table1301differ from the contents of the equivalent tables in the first embodiment.

FIG. 14is an explanatory drawing showing the logical disk control table1300of the second embodiment. The logical disk control table1300has the same format as the logical disk control table112of the first embodiment except that a ‘number of allocated tracks’ column1406is added. The ‘number of allocated tracks’ column1406is a column in which the control processor104registers the number of physical tracks actually allocated to a usable logical disk. This information is needed to enable the control processor104to detect the actual used capacity of the logical disk of a user and allocate physical tracks accordingly instead of immediately allocating the number of physical tracks corresponding to the capacity of the logical disk requested by the user. When the user issues a logical disk capacity allocation request, he or she believes that the logical disk capacity recorded in the total capacity column1404is usable. However, in actuality, because sufficient data to fill the capacity recorded in the total capacity column is not stored, the control processor104does not allocate the number of physical tracks corresponding to the capacity in the total capacity column. In other words, by controlling the allocated capacity of physical tracks in accordance with the actual status of use, the user does not perceive that there is insufficient storage capacity, and therefore does not observe any difference between his requested logical disk capacity and the actually allocated physical disk capacity.

For example, in the example of row1407, 0x00002000 tracks from the start track 0x00000000 of the RAID group 0x00000000 are allocated to the logical tracks 0x00000000 to 0x00001FFF on the logical disk.

FromFIG. 14as a whole, it can be seen that the logical tracks beyond 0x00002800 are not allocated. There is no particular limitation regarding logical track numbers when tracks on a physical disk (here, a RAID group) are allocated.

FIG. 15shows an example of the user management table1301of the second embodiment.

In the user management table1301, as information pertaining to the allocation of logical disks to users of host computers100, in addition to the information stored in the user management table113of the first embodiment, an allocated storage capacity column1504that indicates the physical disk storage capacity that has already been allocated to each logical disk is added.

For example, in the example of row1507of the user management table1301ofFIG. 15, the logical disk 0x00000002 allocated to the user 0x0001 is recognized by a host computer100as a logical disk having a 16 GB storage capacity, and the tracks actually allocated to the logical disk 0x00000002 comprise physical tracks equivalent to 4 GB of storage capacity.

Furthermore, the substantially allocated capacity column1504is a column that corresponds to the number of allocated tracks column1406in the logical disk control table1300, and expresses the capacity in units of bytes.

FIG. 16shows a flow chart indicating the processing by which the capacity of a user's logical disk is increased in accordance with the status of use thereof.

First, the control processor104creates a logical disk in response to the user's allocation request. Here, a logical disk having a capacity equivalent to the user's requested capacity is not created, but rather a logical disk having a fixed capacity is created (step1601). This fixed capacity can be freely set by the administrator or user or set as a prescribed default value. There is no limitation regarding the logical track numbers to be allocated. The numerical values in the logical disk control table1300and the user management table1301are set in response to the numerical value set in this step.

The control processor104then extracts track numbers from the received write command (step1602) and determines whether or not these track numbers are track numbers that have been actually allocated to the logical disk, i.e., whether or not they fall within the range from the start track number1403through the number of allocated tracks1406in the logical disk control table (step1603). If they do fall within this range, the processing to increase the capacity of the logical disk is ended.

If the extracted track numbers do not fall within the above range, the control processor104proceeds to step1604.

In step1604, the control processor104allocates to the logical disk the tracks comprising the increase in the capacity of logical disk and writes the write command data to these allocated tracks. Here, while the control processor104executes processing to allocate the additional tracks to the logical disk, the amount of capacity additionally allocated can be set appropriately in accordance with the running of the storage system.

As described above, if tracks on a physical disk are allocated to a logical disk only to the extent of actual data writing by the user, the number of powered physical disks can be limited to the smallest possible number, thereby enabling the increase in power consumption resulting from such allocation to be minimized. The user does not notice that the capacity of the allocated logical disk is in fact less than the requested capacity. Furthermore, the storage system101ensures that the user can use the entire capacity requested by the user.

While the invention was described using embodiments above, the invention is not limited in any way by these embodiments, and may naturally be implemented in various forms within the essential scope thereof. For example, in the embodiments, the hard disks510were associated with logical disks via a RAID group based on RAID technology, but the hard disks may be associated with logical disks directly without employing RAID technology. Furthermore, in the second embodiment, where the plurality of hard disks include disks having different access speeds, the model of the hard disk to be associated with a logical disk may be selected in accordance with the use status of the logical disk.

The invention is not limited to the form of a storage system, and may be applied using various other forms, such as the form of a program that implements on the computer of a storage system a function to store information handled by a host computer, or the form of a disk control method by which to manage disks belonging to a storage system.