Patent Publication Number: US-8126846-B2

Title: System and method for replicating data

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 10/635,764, filed on Aug. 5, 2003, which is a continuation of U.S. patent application Ser. No. 09/528,416, filed Mar. 17, 2000, which claims priority from Japanese Patent Application Reference No. 11-075174 filed Mar. 19, 1999, the entire contents of which is incorporated herein by reference for all purposes. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates generally to computing systems and more specifically to techniques for controlling copying of logical volumes within a computer storage system. 
     Modern computing systems can comprise a plurality of logical volumes within a mass storage system. Mass storage systems can be implemented in a variety of form factors, including DASD, optical storage media, tape storage media, and the like. Often, it is desirable to perform copies of content from one logical volume to another logical volume in a mass storage system. A conventional method for performing such a copy is known as a REMOTE COPY function. In the REMOTE COPY function, host channels are used for transferring the copied data. A control unit, behaving as if it were a processing unit, sends data stored in a logical volume via a host channel. The data is received by another host channel and written to the logical volume. Thus, a copy of the logical volume is created. 
     When the copy function is executed in one control unit, a plurality of host channels is employed. Therefore, the number of host channels available for the normal host connection is decreased. Such conventional methods typically burden computational resources, such as host channels, during the copy process. 
     What is really needed are techniques for copying information from one logical volume to another without burdening host channel resources for connecting between the control unit and processing units. 
     SUMMARY OF THE INVENTION 
     According to the present invention, techniques for controlling copying of logical volumes within a computer storage system are provided. A representative embodiment includes a plurality of storage devices controlled by a control unit, one or more processors, and a buffer memory for temporarily storing data read from the storage devices within the control unit. The storage devices can be addressed as logical volumes. 
     In an exemplary embodiment, the invention provides a method for creating a copy on a second logical volume of data stored on a first logical volume. The method can comprise a variety of steps, such as specifying a relationship between two or more logical volumes. The method can also include creating a copy of data in a specified first logical volume into said second logical volume. Creating such a copy can include steps of copying data from the first logical volume to a first location in a buffer memory located within a control unit. Copying can be performed by the control unit substantially independently of processor control. Then, data can be copied from the first location in the buffer memory to a second location in the buffer memory. Subsequently, data from the second location in the buffer memory can be copied to the second logical volume. This copying can be performed by the control unit substantially independently of processor control, also. As used herein, substantially independently of processor control can include performing copy processing at the control unit level without necessitating intermediate communication between a command start from the processor to the control unit and a command complete signal from the control unit to the processor. 
     In another embodiment, the invention provides a computer system comprising a plurality of devices. A plurality of storage devices controlled by one or more control units can be part of the computer system. One or more processing units operable to access the control unit or units can also exist in the computer system. A buffer memory operable to temporarily store data read from the storage devices within the control unit can also be part of the computing system. The storage devices can be addressed as one or more logical volumes. The control unit is able to establish a relationship between at least two logical volumes (i.e., a first logical volume and a second logical volume) located in the storage devices. The control unit can create a copy of data in the first logical volume into the second logical volume. Such creating a copy can include copying data from the first logical volume to a first location in the buffer memory. Then, the data can be copied from the first location in the buffer memory to a second location in the buffer memory, changing meta-data indicating the device that may access the data to reflect the second logical volume. Thereupon, the data can be copied from the second location in the buffer memory to the second logical volume. These operations by the control unit can be performed substantially independently of the processing units. In a representative embodiment, the buffer can comprise approximately 10 Gigabytes, for example. 
     In a further embodiment, the invention provides a computer program product for controlling the copying of information from a first logical volume to a second logical volume in a computer system. The computer program product can comprise a computer readable storage medium containing a variety of program code. Code for specifying a relationship between the first logical volume and the second logical volume can be part of the computer program product. The product can also include code for creating a copy of data in the first logical volume into the second logical volume. The code for creating a copy can comprise various program codes. Program code for copying data from the first logical volume to a first location in a buffer memory can be part of the program product. The product can also include code for copying the data from the first location in the buffer memory to a second location in the buffer memory. Code for copying the data from the second location in the buffer memory to the second logical volume can also part of the program product. The codes for copying the data from the first location in the buffer memory to the second location in the buffer memory is executed by a control unit substantially independently of a central processing unit. 
     Select embodiments according to the present invention can be operable with an arrayed disk subsystem. Data may be readily moved to a logical volume having different access characteristics by creating a pair among logical volumes having different RAID levels. Specific embodiments according to the present invention can include a function for creating the data copy, such that, a single logical volume is defined as a primary volume, plural different logical volumes are defined as secondary volumes, and each pair is defined as a different pair. 
     Numerous benefits are achieved by way of the present invention over conventional techniques. Some embodiments according to the present invention can create a copy of specified logical volume without occupying host channels. In such embodiments, control unit load can be reduced. Many embodiments according to the present invention can create a copy at a specified time. Further, in specific embodiments, data in a secondary volume can be used as a series of the historical records of the primary volume switching the secondary volumes one after another. Many embodiments enable data to be replicated more easily, quickly and with improved system loading than heretofore known methods. These and other benefits are described throughout the present specification. A further understanding of the nature and advantages of the invention herein may be realized by reference to the remaining portions of the specification and the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a simplified block diagram of a representative example computing system in a specific embodiment according to the present invention; 
         FIG. 2  illustrates a simplified diagram of a representative command operation in a computing system such as that of  FIG. 1  in a specific embodiment according to the present invention; 
         FIG. 3  illustrates a simplified diagram of representative information operable in a specific embodiment according to the present invention; 
         FIG. 4  illustrates a simplified diagram of representative information operable in a specific embodiment according to the present invention; 
         FIG. 5  illustrates a simplified flow chart of representative copy processing in a specific embodiment according to the present invention; 
         FIG. 6  illustrates a simplified flow chart of representative elemental copy processing in a specific embodiment according to the present invention; 
         FIG. 7  illustrates a simplified diagram of a representative command block format in a specific embodiment according to the present invention; 
         FIG. 8  illustrates a simplified diagram of a representative pair status transition in a specific embodiment according to the present invention; 
         FIG. 9  illustrates a simplified flow chart of representative processing in a specific embodiment according to the present invention; 
         FIGS. 10A-10B  illustrate simplified diagrams of example data replications in a representative computing system in a specific embodiment according to the present invention; and 
         FIGS. 11A-11G  illustrate representative display screens in a specific embodiment according to the present invention. 
     
    
    
     DESCRIPTION OF THE SPECIFIC EMBODIMENTS 
     The present invention provides techniques for controlling copying of logical volumes within a computer storage system. Embodiments according to the present invention can be operable on a wide range of storage devices and systems, for example. Some embodiments can support a buffer memory size of 10 Gigabytes, for example. However, embodiments can support other buffer memory configurations as well. Embodiments can be operable with S/390™, UNIX™, Windows NT™ platforms for example. Many other hardware and software platforms are also suitable for implementing embodiments according to the present invention. 
       FIG. 1  illustrates a simplified block diagram of a representative example computing system in a specific embodiment according to the present invention. This diagram is merely an illustration and should not limit the scope of the claims herein. One of ordinary skill in the art would recognize other variations, modifications, and alternatives.  FIG. 1  illustrates a control unit  102  comprising a cache memory  107 , a channel adapter (“CHA”)  109 , a disk adapter (“DKA”)  108 , a shared memory  110 , for storing control information, for example, and a bus  120  connecting the above mentioned components. A plurality of storage devices  103 ,  104 ,  105 , and  106  can be coupled to control unit  102 . Further, control unit  102  can be coupled to, and can execute commands from, a processing unit  101 . Control information can be transferred from the shared memory  110  to the channel adapter  109  or to the disk adapter  108  via the bus. 
       FIG. 2  illustrates a simplified diagram of a representative command operation in a computing system such as that of  FIG. 1  in a specific embodiment according to the present invention. This diagram is merely an illustration and should not limit the scope of the claims herein. One of ordinary skill in the art would recognize other variations, modifications, and alternatives.  FIG. 2  illustrates representative command set comprising a command name  210 , which can be a create pair command  211 , a delete pair command  212 , a copy command  213  and a re-synchronize command  214 , and the like. 
     Create pair command  211  can be used to establish a pair by specifying a primary volume and a secondary volume. Embodiments can perform an initial copy operation to copy data from the specified primary volume to the specified secondary volume. The primary volume continues to be accessible to applications during the initial copy. In a specific embodiment, a pace may be selected for initial copy operations. Pace can be slow, indicating copy of one track at a time, medium, for three tracks at a time, and fast, for fifteen tracks at a time, for example. Slower paces can minimize use of system resources, while faster paces can accomplish the copy operation sooner. Other embodiments using other or different copy speeds will be readily apparent to one of ordinary skill in the art without departing from the scope of the claimed invention. 
     In a representative embodiment according to the present invention, command processing can perform various actions, such as actions  231 - 263  illustrated in  FIG. 2 , as well as update a command status.  FIG. 8  illustrates a plurality of commands and corresponding status changes in a particular embodiment according to the present invention. For example, a delete pair command  212  can be used to release a pair. Delete pair command processing halts updates to the secondary volume and changes pair status to “no pair” status  801  in  FIG. 8 . A pair can be deleted any time after the pair has been created. Once a pair is deleted, the secondary volume becomes available for write operations upon being unreserved. 
     Copy command  213  can be used to create a copy to a secondary volume. In a presently preferred embodiment, the copy command can cause updates pending for the specified secondary volume to be made. Upon invocation, the pair status changes to “paired/copy in progress” status  803 . Once copy processing has completed, the status can change to “paired and copied” status  804 . An instance of pair tracking information, indicating pair number, primary and secondary volumes and the like, is added to pair information  300  in order to represent the newly created pair. The secondary volume is then made available for read/write access by applications. The primary volume continues to be accessible to applications during create pair command processing. As with create pair command  211  processing, a pace may be selected for update copy operations from among slow, medium and fast. 
     Re-synchronize pair command  214  can bring a status transition to “paired and not copied” status again after a copy is created. In a presently preferred embodiment, re-synchronize pair processing can compare the secondary volume track map with the primary volume track map in control information  401  of  FIG. 4  in order to determine all unequal tracks. Then, unequal tracks can be copied from the primary volume to the secondary volume. As with create pair command  211  processing, a pace may be selected for the re-synchronize copy operations from among slow, medium and fast. 
       FIG. 3  illustrates a simplified diagram of representative information in a specific embodiment according to the present invention. This diagram is merely an illustration and should not limit the scope of the claims herein. One of ordinary skill in the art would recognize other variations, modifications, and alternatives.  FIG. 3  illustrates representative pair information  300  comprising a pair number  301 , a pair status  302 , a primary volume number  303 , a secondary volume number  304 , and a copy pointer  305 . Pair information  300  can be stored in shared memory  110 , for example. Other embodiments can include other information. Further, some embodiments may not comprise all of the elements of pair information  300 . 
       FIG. 4  illustrates a simplified diagram of representative information in a specific embodiment according to the present invention. This diagram is merely an illustration and should not limit the scope of the claims herein. One of ordinary skill in the art would recognize other variations, modifications, and alternatives.  FIG. 4  illustrates representative control information  401 . Control information  401  can facilitate the tracking of inequalities among data sets in a pair. In a particular embodiment, control information  401  comprises an array searchable by pair number  301 , for example. Entries in control information  401  can comprise a set of the inequality information bits, in this embodiment. An inequality information bit can be reset to value of zero (“0”) if the data in corresponding tracks of the primary volume and the secondary volume is equal, and set to a value of one (“1”) if the data is made unequal. Control information  401  can be stored in shared memory  110 , for example. 
       FIG. 5  illustrates a simplified flow chart of representative copy processing in a specific embodiment according to the present invention. This diagram is merely an illustration and should not limit the scope of the claims herein. One of ordinary skill in the art would recognize other variations, modifications, and alternatives.  FIG. 5  illustrates representative copy command processing  500 . Copy command processing  500  can be initiated responsive to receiving a create pair command  211  or create copy command  213 , with a pair number as input parameters, for example. In a decisional step  501 , the control unit searches pair information  300  for an entry having the same pair number as specified in the input information. Once a suitable entry is located, the pair status  302  of the entry is checked and a determination is made whether the pair status is “paired and not copied” status  802 . If the pair status is not “paired and not copied” status  802 , a determination is made that the copy command should not continue and copy processing is terminated. If the pair status is “paired and not copied” status  802 , then in a step  502 , an elemental copy processing  600  is initiated with the pair number as an input parameter. After elemental copy processing  600  completes, then in a decisional step  503  a determination is made whether any further copy processing is to be performed. In a specific embodiment, decisional step  503  can comprise checking a copy pointer  305  for a match with the maximum address of the logical volume. If the copy pointer  305  does not match the maximum address, the copy processing is determined to be incomplete and processing continues by repeating step  501 . Otherwise, if a match is found, then no further copying remains and processing continues with a step  504 . In step  504 , the pair status  302  is changed to “paired and copied” status and copy processing is complete. 
       FIG. 6  illustrates a simplified flow chart of representative elemental copy processing in a specific embodiment according to the present invention. This diagram is merely an illustration and should not limit the scope of the claims herein. One of ordinary skill in the art would recognize other variations, modifications, and alternatives.  FIG. 6  illustrates elemental copy processing  600 . Elemental copy processing  600  includes a step  601 , in which a control unit searches pair information  300  for an entry having the same pair number as specified in the input information. Then, in a step  601 , the control unit can fetch the copy pointer  305  related to the selected entry. Next, in a step  602 , the control unit searches control information  401  for data having an inequality bit set to a value of one (“1”) using the address specified by the copy pointer  305  fetched in step  601 . Next, in a step  603 , the control unit reads the data referred to in step  602  from the primary volume and stores it in cache memory  107 . In a step  604 , the data stored in the cache memory in step  603  is copied to another location in the cache memory  107  and the logical volume number included in the copied data is changed to the secondary volume number  304  from the primary volume number  303 . Then, in a step  605 , the data copied in step  604  is written to the secondary volume. In a step  609 , the inequality bits related to the data written to the secondary volume are reset to a value of zero (“0”). Next, in a step  606 , the copy pointer  305  is advanced by an amount corresponding to the amount of data written to the secondary volume. In a step  607 , the copy pointer modified in step  606  is stored in the pair information  300 , the elemental copy processing is completed, and processing returns to the caller in a step  608 . 
       FIG. 7  illustrates a simplified diagram of a representative command block format in a specific embodiment according to the present invention. This diagram is merely an illustration and should not limit the scope of the claims herein. One of ordinary skill in the art would recognize other variations, modifications, and alternatives.  FIG. 7  illustrates a representative command block comprising a command code  701 , a primary volume number  702 , and a secondary volume number  703 . When a control unit  102  receives a command block, it searches pair information  300  for pair entries having the same combination of primary volume number  303  and secondary volume number  304  as that of the primary volume number  702  and secondary volume number  703  specified in the command block. The control unit obtains the pair status  302  from this entry and initiates the processing shown in  FIG. 2  based upon the command code  701  stored in command block  700 . 
     For example, if the status of the pair specified by a create pair command  211  is “no pair” status  221 , the control unit initiates create a new pair processing  231 . In a specific embodiment, an empty entry is assigned to the pair information  300 . A pair comprising a primary volume number and a secondary volume number specified in the create pair command  211  can be set into the area of primary volume number  303  and the area of secondary volume number  304  in the pair information  300  respectively. A copy pointer  305  is initialized, and then copy process  500  is initiated. 
     If the pair specified in create pair command  211  is in a status other than “no pair” status  221 , the control unit does nothing. If the pair specified in a delete pair command  212  has “no pair” status  221 , the control unit does nothing. If the pair specified in a delete pair command  212  is in paired status  222  or  223 , the control unit initializes the entry of the pair information  300  corresponding to the specified pair. 
     If the pair specified by a create copy command  213  is in “no pair” status  221 , the control unit does nothing. If the pair specified in a create copy command  213  is in “paired and not copied” status  222 , the control unit sets the inequality bit in the control information table  401  to a value of one (“1”) for the data of the specified volume. Then, the control unit initializes the copy pointer  305 , and invokes the copy processing  500 . If the pair specified by a create copy command  213  is in “paired and copied” status  223 , the control unit does nothing. 
     If the pair specified by re-synchronize pair command  214  is in “no pair” status  221 , the control unit does nothing. If the pair specified by re-synchronize pair command  214  is in “paired and not copied” status  222 , the control unit does nothing. If the pair specified by a re-synchronize pair command  214  is in “paired and copied” status  223 , the control unit changes the current pair status to “paired and not copied” status  222 . 
       FIG. 8  illustrates a representative pair status transition diagram for pair status  302  in a typical entry of pair information  300  in a specific embodiment according to the present invention. This diagram is merely an illustration and should not limit the scope of the claims herein. One of ordinary skill in the art would recognize other variations, modifications, and alternatives. In  FIG. 8 , a “no pair” status  801  indicates that a pair has not been established. A “paired and not copied” status  802  indicates that a pair has been established but a copy to the secondary volume has not been initiated yet. A “paired and copy in progress” status  803  indicates that copy processing to the secondary volume is being executed. A “paired and copied” status  804  indicates that copy to the secondary volume is complete. 
     A delete pair command  212  causes a status transition to “no pair” status  801  from any status. A create pair command  211  causes a status transition to “paired and not copied” status  802  from “no pair” status  801 . A create copy command  213  causes a status transition to “paired and copy in progress” status  803  from “paired and not copied” status  802 . Copy processing  500  completion causes a status transition to “paired and copied” status  804  from “paired and copy in progress” status  803 . A re-synchronize pair command  214  causes a status transition to “paired and not copied” status  802  from “paired and copied” status  804 . 
       FIG. 9  illustrates a simplified flow chart of representative change request processing in a specific embodiment according to the present invention. This diagram is merely an illustration and should not limit the scope of the claims herein. One of ordinary skill in the art would recognize other variations, modifications, and alternatives. A request to change the data in a primary volume may be made during a copy process, for example.  FIG. 9  illustrates a step  901 , in which a control unit, such as control unit  102  of  FIG. 1 , for example, searches the pair information  300  for entries having the same primary volume number as the volume number specified in the input information for the change request. In a step  902 , the control unit fetches the pair status  302  from the entry corresponding to the pair number obtained in step  901  and checks if the pair status is in “paired and copy in progress” status  803 . 
     If the status is not “paired and copy in progress” status  803 , then the control unit executes a normal write processing in a step  909 . Otherwise, if the status is “paired and copy in progress” status  803 , then control unit processing continues with a step  903 . In step  903 , the control unit searches the control information  400  corresponding to the data to be modified as requested by the processing unit  101 . The control unit can perform this searching using the pair number obtained in step  901 . Once located, the control unit checks the corresponding inequality bit for a value of one (“1”). If the bit does not have a value of one, then the control unit processing continues with step  909 , which executes normal write processing. Otherwise, if the bit is a one, then the control unit processing continues with a step  904 . In step  904 , the data to be modified is read from the primary volume into the cache memory. Then, in a step  905 , the data read into the cache memory in step  904  is copied in the buffer memory for the secondary volume and the logical volume number included in the copied data is changed to the secondary volume number  304  from the primary volume number  303 . Then, in a step  906 , the data copied in step  905  is written to the secondary volume. Next, in a step  907 , the inequality bit corresponding to the data written to the secondary volume is reset to zero (“0”). In step  909 , the control unit writes the data to be transferred to the primary volume. 
       FIG. 10A  illustrates a simplified block diagram of a representative example of copying data between logical volumes in a specific embodiment according to the present invention. This diagram is merely an illustration and should not limit the scope of the claims herein. One of ordinary skill in the art would recognize other variations, modifications, and alternatives.  FIG. 10A  illustrates a control unit  1002  comprising a cache memory  1007 , a channel adapter (“CHA”)  1009 , a disk adapter (“DKA”)  1008 , which are interconnected by a bus (not shown). A plurality of storage devices  1003  and  1004  can be coupled to control unit  1002  via disk adapter  1008 , and storage devices  1005  and  1006  can be coupled to control unit  1002  via disk adapter  1010 . Further, control unit  1002  can be coupled to, and can execute commands from, a processing unit  1001 . Control information can be transferred from a shared memory (not shown) to the channel adapter  1009  or to the disk adapters  1008  and  1010  via the bus. 
     Arrow number one indicates a host write command sent from the processor  1001  to control unit  1002 . Arrow two illustrates a device end that is sent from channel adapter  1009  to processor  1001 . Disk adapter  1008  performs a copy of data from primary logical volume  1003  into a first location  1300  in cache memory  1007 , as indicated by arrow three. Thereupon, a second copy of the data is made into a second location  1302  in cache memory  1007  and the logical volume number included in the copied data is changed from the primary volume number to the secondary volume number, as indicated by arrow four. As indicated by arrows five and six, the data is copied by disk adapter  1010  into storage device  1006  in order to complete the copy. 
       FIG. 10B  illustrates a simplified block diagram of a representative example of copying data between locations in a cache memory in a specific embodiment according to the present invention. This diagram is merely an illustration and should not limit the scope of the claims herein. One of ordinary skill in the art would recognize other variations, modifications, and alternatives.  FIG. 10B  illustrates an address change unit  1020 , which in a representative embodiment can be a data recovery and reconstruction (DRR) unit, for example, having a buffer  1021 , a cache  1022 , a first physical device  1024  and a second physical device  1026 . In a particular embodiment, address change unit  1020  can be located within a disk adapter unit, such as disk adapter  108  of  FIG. 1 , for example. First physical device  1024  and second physical device  1026  can be of many types of storage devices, such as storage devices  103 ,  104 ,  105  and  106  of  FIG. 1 , for example. Cache  1022  can be cache memory  107 , for example. Data can be comprise a user data section  1027 , a logical address section  1029  and a check code section  1031 , for example. 
     In a specific embodiment according to the present invention, a copy process can execute on DKA processors, for example. A first cache location  1022   a  and a second cache location  1022   b  can be secured in cache  1022 , for example, to correspond to the first physical device  1024  and second physical device  1026 , respectively. A command can be issued to address change unit  1020  to perform a copy of data stored in first physical device to a second physical device. Arrows  1 ,  2 ,  3  and  4  illustrate processing of such a command in a representative embodiment. Arrow  1  indicates a copy of the data from the first physical device  1024  into a first cache location  1022   a . Then, as indicated by arrow  2 , the data is moved from first cache location  1022   a  into buffer  1021 . While data is contained in buffer  1021 , a logical address, LA, portion within the data can be changed from indicating a device number (DEV) of first physical device  1024  to a device number of second physical device number  1026 . A check code, CD, which can be parity or other type of check data, can be updated to reflect the change in the LA. Arrow  3  illustrates copying of the data from the buffer  1021  into a second location  1022   b  within cache  1022 . Arrow  4  indicates a copy of the information from the second location  1022   b  in cache  1022  into second physical device  1026 . 
       FIGS. 11A-11G  illustrate representative display screens in a specific embodiment according to the present invention.  FIG. 11A  illustrates a representative user interface screen  1500  having a display mode selection area  1501 . This diagram is merely an illustration and should not limit the scope of the claims herein. One of ordinary skill in the art would recognize other variations, modifications, and alternatives. Display mode selection area  1501  enables the user to select either a volume display mode, such as illustrated by  FIG. 11A , or a pair display mode, such as illustrated by  FIG. 11B , using a selection button mechanism. A port selection field  1502  enables the user to specify a desired port, as well as all ports. A volume display control area  1503  becomes active when volume display mode is selected in display mode selection area  1501 . Volume display control area  1503  enables the user to “filter” the volumes displayed in a volume list display area  1504 . Filtering can be performed by reserve attribute and by pair condition, for example. An attribute reserve box  1505  enables the user to display reserved or unreserved volumes. Furthermore, volume pair/no pair selection boxes  1506  enable the display of paired and/or non-paired volumes. When volume display mode is selected in display mode selection area  1501 , the volume display area  1504  lists installed volumes (LUs) on the selected port and displays information for each volume. Volume display area  1504  provides information about storage. In a present embodiment, such information can include a port identifier, comprising a cluster and channel number, for each volume. A target identifier, including an LU number, for each volume can also be included in display area  1504 . Further, display area  1504  can also include a volume number, comprising a control unit and logical device identifier for each volume, a number of pairs formed with the volume. A status of the volume, including normal, blocked, format, correct, copying, or unknown, a d device emulation type (e.g., OPEN-3, OPEN-9), and a storage capacity of the volume can also be displayed. 
     A pair display control area  1507  enables the user to “filter” the pairs displayed in the volume display area  1504  by pair status. Pair status can include simplex, pending, duplex, split, re-sync, suspend, SP-Pending, for example. A Define status display area  1508  provides a display of DASD usage, including the total number of open system volumes, total and maximum number of reserved volumes and total and maximum number of pairs. 
     A plurality of buttons along the right side of the screen of  FIG. 11A  enable the user to perform the following operations. A Pair Status button  1510  displays the pair status for the selected volume(s)/pair(s). A Stat&amp;History button  1511  displays the pair status and history for the selected volume(s)/pair(s). An Add Pair button  1512  enables new pairs to be added. A Delete Pair button  1513  allows pairs to be deleted. Suspend Pair button  1509  enables suspending of a pair. A Split Pair button  1514  allows the user to copy the contents of a source logical volume to a target logical volume in a pair. A Re-sync Pair button  1515  enables the user to re-synchronize pairs. An Attribute button  1516  enables the set/reset of reserve attributes. A T-VOL Path button  1517  displays the secondary logical volume SCSI paths for the selected pair(s). A Refresh button  1518  updates the information displayed. An Exit button  1519  returns to a previous panel. 
       FIG. 11B  illustrates a representative volume list display area in a particular embodiment according to the present invention. This diagram is merely an illustration and should not limit the scope of the claims herein. One of ordinary skill in the art would recognize other variations, modifications, and alternatives.  FIG. 11B  illustrates volume display area  1504  displaying information about pairs. Information such as port identifiers, logical unit number, control unit numbers and logical device identifiers and volume status can be displayed for both primary and secondary volumes. Additionally, a pair status can be displayed for the volume pair. 
       FIG. 11C  illustrates a representative panel for adding a pair in a particular embodiment according to the present invention. This diagram is merely an illustration and should not limit the scope of the claims herein. One of ordinary skill in the art would recognize other variations, modifications, and alternatives.  FIG. 11C  illustrates add pair dialog panel  1520  that can be opened by selecting Add Pair button  1512  on screen  1500  of  FIG. 11A . Panel  1520  displays the primary (“S-VOL”) and secondary (“T-VOL”) information for the pair(s) being added. In a present embodiment, information can include a port, a TID, a LUN, a CU image, an LDEV ID, volume status and emulation type. The secondary volume corresponding to each primary volume can be displayed once the primary volume has been selected. The user can select a secondary volume (i.e., the T-VOL(s)) for each primary volume (i.e., the S-VOL) by highlighting the primary volume in display area  1521 , then scrolling through a list of secondary volumes within the volume display area  1522 . The user can select a copy pace for adding the pairs using copy pace selection pull down  1523 . Copy pace can be slow (one track at a time), medium (three tracks at a time) or fast (fifteen tracks at a time). 
     Volume display area  1522  displays detailed volume information for a selected pair, including S-VOL ID (port, TID: LUN, CU: LDEV), storage capacity, and number of existing pairs. A T-VOL display area  1524 , within volume display area  1522 , enables selection of a secondary volume automatically or manually. When Auto is selected, the SVP selects the secondary volume from the set of reserved volumes by LDEV ID (in ascending order, lowest to highest). When Select is selected, the Volume and Port display options can be used to display the available secondary volumes by port and by reserve attribute. 
     A plurality of buttons includes a Change button  1525 , which replaces the secondary volume for the selected primary as specified. A Set button  1526  adds an additional secondary volume to the selected primary volume as specified. An Omit button  1527  deletes the selected primary volume(s)/pair(s) from the list of pairs. An Undo button  1528  undoes the previous Change or Set command. An Add button  1529  adds all pairs in the list. An Exit button  1530  closes dialog panel  1520 . 
       FIG. 11D  illustrates a representative panel for displaying pair status and history information in a particular embodiment according to the present invention. This diagram is merely an illustration and should not limit the scope of the claims herein. One of ordinary skill in the art would recognize other variations, modifications, and alternatives.  FIG. 11D  illustrates status and history panel  1531  that can be opened by selecting Status&amp;History button  1511  on screen  1500  of  FIG. 11A . Panel  1531  comprises a status display area  1532  and a history display area  1533 . Status display area  1532  can display information for a selected port, for example. Representative pair information for pairs associated with the port can include a primary volume identifier, a secondary volume identifier, a pair status, a copy pace, a date and time that the information was acquired (panel opened/refreshed), and the like. A Refresh Status button  1534  updates the information in status display area  1532 . A T-VOL Path button  1535  displays secondary volume SCSI paths for a selected pair or pairs. The History display area  1533  can display history information for a selected port. Displayed pair activity information can be ordered according to date and time, primary volume and secondary volume (CU: LDEV), as well as a volume code and a message type. A Date Time button  1536  sorts the list by date and time. An S-VOL button  1537  and T-VOL button  1538  can cause the list to be sorted by primary volume or secondary volume, respectively. A Code button  1539  can cause the list to be sorted by code number, and a Message button  1540  can cause the list to be sorted according to message type. A current primary volumes display area  1541  and current secondary volumes display area  1542  can display primary and secondary volumes currently used, respectively. A Refresh History button  1543  refreshes the pair history information for the selected port. A Refresh All button  1544  updates all information on the Status &amp; History panel. An Exit button  1545  exits the Status &amp; History panel and returns panel  1500 . 
       FIG. 11E  illustrates a representative panel for creating a copy of a primary volume to a secondary volume in a particular embodiment according to the present invention. This diagram is merely an illustration and should not limit the scope of the claims herein. One of ordinary skill in the art would recognize other variations, modifications, and alternatives.  FIG. 11E  illustrates split volume panel  1550  that can be opened by selecting Split pair button  1514  on screen  1500  of  FIG. 11A . Split volume pair panel  1550  provides the capability to copy data from a primary volume to secondary volumes for pairs in a list of pair(s) selected on panel  1500 , showing the pair status and copy pace for each pair. In a present embodiment, information can include a port, a TID, a LUN, a CU image, an LDEV ID, volume status and emulation type. The secondary volume corresponding to each primary volume can be displayed once the primary volume has been selected by highlighting the primary volume in display area  1551 . The user can select a copy pace for copying data from the primary to the secondary volume of the pairs using copy pace selection pull down  1553 . Copy pace can be slow (one track at a time), medium (three tracks at a time) or fast (fifteen tracks at a time) in a representative embodiment. 
     Volume display area  1552  displays detailed volume information for a selected pair, including S-VOL ID (port, TID: LUN, CU: LDEV), storage capacity and number of existing pairs. Users can change or add secondary volumes to a primary volume using this panel. A T-VOL display area  1554 , within volume display area  1552 , enables selection of a secondary volume automatically or manually. When Auto is selected, the SVP selects the secondary by LDEV ID. When Select is selected, the volume and port display options can be used to display the available secondary volumes by port and by reserve attribute. 
     A plurality of buttons includes a Change button  1555 , which replaces the secondary volume for the selected primary as specified. A Set button  1556  adds an additional secondary volume to the selected primary volume as specified. An Omit button  1557  deletes the selected primary volume(s)/pair(s) from the list of pairs. An Undo button  1558  undoes the previous Change or Set command. A split button  1559  splits all pairs in the list. An Exit button  1560  closes dialog panel  1551 . 
       FIG. 11F  illustrates a representative panel for providing the capability to re-synchronize data sets in a pair comprising a primary volume and a secondary volume in a particular embodiment according to the present invention. This diagram is merely an illustration and should not limit the scope of the claims herein. One of ordinary skill in the art would recognize other variations, modifications, and alternatives.  FIG. 11F  illustrates resynchronize volume pair panel  1561 . Panel  1561  comprises pair list  1562 , listing pair(s) selected from panel  1500  and shows the pair status and copy pace for each pair. The user can select a copy pace for copying data from the primary to the secondary volume of the pairs using copy pace selection pull down  1563 . Copy pace can be slow (one track at a time), medium (three tracks at a time) or fast (fifteen tracks at a time) in a representative embodiment. A Re-sync button  1564  starts the re-synchronize operation for the specified pair(s). An Exit button  1565  closes panel  1561 . 
       FIG. 11G  illustrates a representative panel for providing the capability to delete pairs comprising a primary volume and a secondary volume in a particular embodiment according to the present invention. This diagram is merely an illustration and should not limit the scope of the claims herein. One of ordinary skill in the art would recognize other variations, modifications, and alternatives.  FIG. 11G  illustrates delete volume pair panel  1571 . Panel  1571  comprises pair list  1572 , listing pair(s) selected from panel  1500  and shows the pair status for each pair. A delete button  1574  deletes the specified pair(s). An Exit button  1575  closes panel  1571 . 
     CONCLUSION 
     Although the above has generally described the present invention according to specific systems, the present invention has a much broader range of applicability. In particular, the present invention is not limited to a particular kind of computing system, nor a particular type of storage device. Thus, in some embodiments, the techniques of the present invention could provide the capability to make copies of data resident on many different types of computer storage systems. The specific embodiments described herein are intended to be merely illustrative and not limiting of the many embodiments, variations, modifications, and alternatives achievable by one of ordinary skill in the art. Thus, it is intended that the foregoing description be given the broadest possible construction and be limited only by the following claims. 
     The preceding has been a description of the preferred embodiment of the invention. It will be appreciated that deviations and modifications can be made without departing from the scope of the invention, which is defined by the appended claims.