Abstract:
A method is provided to improve the efficiency of the transmission of consistency groups across multiple storage components by ensuring that volume transactions are evenly allocated among backup components. Each volume is initially assigned to a specified backup component. Once a color period begins, volume transactions are transmitted to the assigned backup component. Each backup component accumulates data transfer information for its assigned volumes throughout at least a portion of the color period and calculates a new volume assignment for the next color period. Before the start of the next color period, a captain storage controller transmits any new assignments to the backup components. During a next color period, the process is repeated using the new assignments.

Description:
TECHNICAL FIELD 
     The present invention relates generally to the transfer of data within a data storage system and particularly to balancing such transfers among components in the data storage system. 
     BACKGROUND ART 
     Disaster recovery systems typically address two types of failures: a sudden catastrophic failure at a single point in time, or data loss over a period of time. In both types of failure scenario, updates to volumes may be lost. To assist in recovery of data updates, a copy of data may be provided at a remote location. Such dual or shadow copies are typically made as the application system is writing new data to a primary storage device. International Business Machines Corporation (IBM®), the assignee of the subject patent application, provides the following systems for maintaining remote copies of data at a secondary site, Extended Remote Copy (XRC) and Peer-to-Peer Remote Copy (PPRC). These systems provide a method for the continuous mirroring of data to a remote site to failover to during a failure at the primary site from which the data is being continuously mirrored. Such data mirroring systems can also provide an additional remote copy for non-recovery purposes such as local access at a remote site. These IBM XRC and PPRC systems are described in the IBM publication “Remote Copy: Administrator&#39;s Guide and Reference,” IBM document number SC35-0169-02 (IBM Copyright 1994, 1996), which publication is incorporated herein by reference in its entirety. 
     In such backup systems, data is maintained in volume pairs. A volume pair is comprised of a volume in a primary storage device and a corresponding volume in a secondary storage device that includes an identical copy of the data maintained in the primary volume. Typically, the primary volume of the pair will be maintained in a primary direct access storage device (DASD) and the secondary volume of the pair is maintained in a secondary DASD shadowing data from the primary DASD. A primary storage controller may be provided to control access to the primary DASD and a secondary storage controller may be provided to control access to the secondary DASD. In the IBM XRC environment, the application system writing data to the primary volumes includes a sysplex timer which provides a time-of-day (TOD) value as a time stamp to data writes. The host system time stamps data sets when writing such data sets to volumes in the primary DASD. The integrity of data updates is related to insuring that updates are done at the secondary volumes in the volume pair in the same order as they were done on the primary volume. In XRC and other prior art systems, the cross systems common time stamp provided by the system on behalf of the application program determines and maintains the logical sequence of data updates across any number of data volumes on any number of storage systems. In many application programs, such as database systems, certain writes cannot occur unless a previous write occurred; otherwise the data integrity would be jeopardized. Such a data write whose integrity is dependent on the occurrence of a previous data write is known as a dependent write. For instance, if a customer opens an account, deposits $400.00, and then withdraws $300.00, the withdrawal update to the system is dependent on the occurrence of the other writes, i.e., the opening of the account and the deposit. When such dependent transactions are copied from the primary volumes to the secondary volumes, the transaction order must be maintained to maintain the integrity of the dependent write operation. 
     Volumes in the primary and secondary DASDs are consistent when all writes have been transferred in their logical order, i.e., all writes have been transferred before the writes which are dependent upon them. In the banking example, this means that the deposit is written to the secondary volume before the withdrawal. A consistency group is a collection of updates to the primary volumes such that dependent writes are secured in a consistent manner. For instance, in the banking example, this means that the withdrawal transaction is in the same or a later consistency group as the deposit; the withdrawal cannot be in an earlier consistency group. Consistency groups maintain data consistency across volumes, storage devices and storage systems. For instance, if a failure occurs, the deposit will be written to the secondary volume before the withdrawal. Thus, when data is recovered from the secondary volumes, the recovered data will be consistent. 
     A consistency time is a time the system derives from the application system&#39;s time stamp to the data set. A consistency group has a consistency time for all data writes in a consistency group having a time stamp equal to or earlier than the consistency time stamp. In the IBM XRC environment, the consistency time is the latest time to which the system guarantees that updates to the second volume are consistent. If all the records in the consistency group are written to secondary volumes during a period of time referred to as a “color period”, then the reported consistency time reflects the latest time stamp of all records in the consistency group. Methods for maintaining the sequential consistency of data writes and forming consistency groups to maintain sequential consistency in the transfer of data between a primary DASD and secondary DASD are described in commonly assigned U.S. Pat. Nos. 5,615,329 and 5,504,861 which are incorporated herein by reference in their entirety. 
     Within a consistency group, redundant data may be eliminated because only the latest version of a block need be retained. However, when data is spread across multiple components, it may be difficult to coordinate the elimination of redundant data unless the final compilation for each volume is handled by a single backup component. Commonly assigned and co-pending U.S. patent application Ser. No. 10/618,242, entitled “AUTONOMIC LINK OPTIMIZATION THROUGH ELIMINATION OF UNNECESSARY TRANSFERS” and filed on Jul. 11, 2003, is incorporated herein by reference and describes the process of ensuring that a single backup component receives all of the data for a particular volume during a particular color. Additionally, the amount of data received by a backup component may be disproportionately large relative to the amount of data received by other backup components, thereby increasing the time to transfer all of the volumes to all of the backup components. 
     Thus, a need exists to improve the efficiency of the transmission of consistency groups across multiple storage components. 
     SUMMARY OF THE INVENTION 
     The present invention provides a method to improve the efficiency of the transmission of consistency groups across multiple storage components by ensuring that volume transactions are evenly allocated among backup components. Each volume is initially assigned to a specified backup component. Once a color period begins, volume transactions are transmitted to the assigned backup component. Each backup component accumulates data transfer information for its assigned volumes throughout at least a portion of the color period and calculates a new volume assignment for the next color period. Before the start of the next color period, a captain storage controller transmits any new assignments to the backup components. During a next color period, the process is repeated using the new assignments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram illustrating a network computing environment in which aspects of the invention are implemented; 
         FIG. 2  illustrates an arrangement of a storage controller in accordance with implementations of the present invention; 
         FIGS. 3A and 3B  are flow charts of operations performed by storage controllers to manage load balancing in accordance with the present invention; and 
         FIG. 4  illustrates an architecture of computing components in the network environments, such as the storage controllers, used with implementations of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In the following description, reference is made to the accompanying drawings which form a part hereof and which illustrates several embodiments of the present invention. It is understood that other embodiments may be utilized and structural and operational changes may be made without departing from the scope of the present invention. 
       FIG. 1  illustrates a network computing environment in which aspects of the invention may be implemented. A local site  2  includes storage controllers  4 A,  4 B,  4 C coupled to attached storage systems  6 A,  6 B,  6 C, respectively. The storage controllers  4 A,  4 B,  4 C manage input/output (I/O) access to volumes in the storage systems  6 A,  6 B,  6 C from local host  18 . Each storage controller  4 A,  4 B,  4 C copies data to a corresponding local backup components  5 A,  5 B,  5 C, respectively. Each local backup component  5 A,  5 B,  5 C copies data to a remote backup component  9 A,  9 B,  9 C, respectively, at a remote site  10  via connections  12 A,  12 B,  12 C. The local backup components  5 A,  5 B,  5 C transmit data consistent as of a point of time to the remote backup components  9 A,  9 B,  9 C, where remote storage controllers  8 A,  8 B,  8 C store the data to respective attached remote storage systems  14 A,  14 B,  14 C. In certain implementations, the local backup components  5 A,  5 B,  5 C continuously transmit data to the remote site  10 , and at certain instances in time will ensure the consistency of the data at the remote site  10 . In certain implementations, the remote site  10  may save a consistency group of data to another storage, such as consistent backup storages  16 A,  16 B,  16 C to maintain a backup of the consistent data at the remote site  10 . After a consistent group of data is transmitted to the remote storage  14 A,  14 B,  14 C, a copy is made from remote storage  14 A,  14 B,  14 C to a respective consistent backup storage  16 A,  16 B,  16 C. Although  FIG. 1  illustrates a certain number of components at the sites, such as three sets of storage controllers, storage systems and backup components, the described implementations may operate with any number of storage controllers, storage systems and backup components at the sites. Moreover, through use of network connections, any local backup component  5 A,  5 B,  5 C may be connected to any remote backup component  9 A,  9 B,  9 C. 
     The remote site  10  may be hundreds or thousands of miles from the local site  2 . The connections  12 A,  12 B,  12 C between pairs of backup components may comprise a dedicated line, such as a dedicated fiber optical network or connection maintained by a long distance telecommunication carrier, long distant fiber optic connection having channel extenders, or extend through a network such as a storage area network (SAN), local area network (LAN), the internet, an intranet, etc. 
     The local host  19  at the local site  2  may perform I/O operations with respect to volumes in the local storage systems  6 A,  6 B,  6 C. The local host  19  may communicate with storage controllers  4 A,  4 B,  4 C via any network or connection known in the art. The storage controllers  4 A,  4 B,  4 C at the local site may have certain relationships with respect to the volumes managed by the storage controllers. One backup component may be designated as a “captain”, e.g.,  5 C. The captain backup component may accumulate information about volumes as transactions are written as well as assign volume ownership to back-up components  9 A,  9 B,  9 C. 
     The storage controllers  4 A,  4 B,  4 C and remote storage controllers  8 A,  8 B,  8 C further include a processor complex and may comprise any storage controller or server known in the art such as the IBM Enterprise Storage Server® (ESS), 3990Storage Controller, etc. The local storage systems  6 A,  6 B,  6 C, remote storage systems  14 A,  14 B,  14 C and backup storage systems  16 A,  16 B,  16 C may comprise an array of storage devices such as just a bunch of disks (JBOD), redundant array of independent disks (RAID), virtualization device, etc. 
     The local storage controllers  4 A,  4 B,  4 C and backup components  5 A,  5 B and  5 C may communicate over a local network  18  which may comprise direct connections or a switched network. Alternatively, the storage controllers  4 A,  4 B,  4 C and backup components  5 A,  5 B and  5 C may communicate over links  12 A,  12 B,  12 C to the remote site  10  if the links also extend through a network at the local site  2 . 
       FIG. 2  illustrates programs and information that may be included in the captain backup component  5 A at the local site  2 , including storage management software  62  and relationship assignment information  64 . The storage management software  62  may include code to assign each volume to backup component in the remote site  10 , compile information about the capacity of each backup component as volume transactions are transmitted to the assigned backup components, and reassign volumes as appropriate in order to more evenly balance the load among the backup components. 
       FIG. 3A  is a flow chart illustrating operations performed by the captain backup component  5 C, to manage volume assignments and load balancing. Each volume is initially assigned to a specified backup component (step  300 ). The initial assignment may be performed arbitrarily because no history has yet been accumulated on which to base more refined assignments. One such method of initial assignments is to distribute volumes evenly across all of the backup components. Volume transactions are then written to the assigned backup components during a color period (steps  310 ,  320 ). While the color period continues, each backup component accumulates data transfer information for its assigned volumes. The captain backup component  5 C collects the volume by volume information from the backup components and determines whether any backup components are receiving more than a proportionate share of the volumes (step  330 ). Such accumulation continues for a predetermined period which may be shorter than the full color period. Before the beginning of the next color period, the captain backup component  5 C performs a reallocation of volume assignments to more evenly distribute the volumes across the backup components during the next color period (step  340 ). For example, the captain backup component  5 C may reassign a first volume to the backup component to which the smallest percentage of expected work has already been assigned. Similarly, the next volume is reassigned to the backup component to which the smallest percentage of expected work has then already been assigned, and so forth until all of the volumes have been reassigned. Before the color period has completed (step  360 ), all backup components briefly pause in a point-in-time consistent manner and the captain backup component  5 C transmits new assignments (if any) (step  350 ). After the first color periods ends, the next color period may commence (step  370 ) and the backup components resume receiving transactions based on any new assignments. During each subsequent color period, the captain backup component  5 C may adaptively re-assign volumes as conditions change (steps  320 - 370 ). 
     In a more detailed description of the forgoing method of reassigning volume ownership (step  320 ) illustrated in the flow chart of  FIG. 3B , the captain backup component  5 C uses the volume by volume data transfer information and any previously acquired knowledge to determine the expected amount of work for each volume for the next color period (step  332 ). The volumes are sorted in order of the expected amount of work for the next color period (step  334 ). The amount of work assigned to each backup component is set to zero (step  336 ). Volumes may then be reassigned to backup components based upon the expected amount of work of each backup component (step  338 ). The algorithm attempts to minimize the time it will take the backup component with the most work to do to send its transaction data to the secondary backup component. The optimal distribution of work is such that each backup component does exactly the same amount of work, and thus no backup component is ever idle. 
     The captain assigned may also maintain a record of historical trends in the amount of data received for each volume over several color periods. For example, volume A may have received 50% of the data during the first color period, 40% during the second and 30% during the third. The captain assigned may assume that the relative amount of data received by volume A during the fourth color period would be still less, such as 20%, and determine an ownership assignment according to the assumption. 
     In an alternative arrangement, no single backup component functions as the captain. Rather, the backup components may be configured to obtain the information about how much data has been received for each volume. A reassignment algorithm is then executed by each backup component, with each examining the volumes in the same order so that each backup component generates the same re-assignments. Re-assignment of volumes may then be performed independently by each backup component. 
     The described techniques to form consistency groups may be implemented as a method, apparatus or article of manufacture using standard programming and/or engineering techniques to produce software, firmware, hardware, or any combination thereof. The term “article of manufacture” as used herein refers to code or logic implemented in hardware logic (e.g., an integrated circuit chip, Programmable Gate Array (PGA), Application Specific Integrated Circuit (ASIC), etc.) or a computer readable medium (e.g., magnetic storage medium such as hard disk drives, floppy disks, tape), optical storage (e.g., CD-ROMs, optical disks, etc.), volatile and non-volatile memory devices (e.g., EEPROMs, ROMs, PROMs, RAMs, DRAMs, SRAMs, firmware, programmable logic, etc.). Code in the computer readable medium is accessed and executed by a processor. The code in which implementations are made may further be accessible through a transmission media or from a file server over a network. In such cases, the article of manufacture in which the code is implemented may comprise a transmission media such as network transmission line, wireless transmission media, signals propagating through space, radio waves, infrared signals, etc. Of course, those skilled in the art will recognize that many modifications may be made to this configuration without departing from the scope of the implementations and that the article of manufacture may comprise any information bearing medium known in the art. 
     The above implementations were described with respect to a specific environment. However, the described implementations for maintaining consistency during recovery processes could be applied to maintain consistency in other computing and vendor environments and using other data copying protocols and programs than described herein. 
     In certain implementations, data in the storage devices is arranged in volumes. In alternative systems, the storage areas on which data is maintained may be grouped according to storage units other than volumes that are grouped in groupings other than sessions for the purpose of maintaining consistency. 
     The illustrated logic of  FIGS. 3A and 3B  show certain events occurring in a certain order. In alternative implementations, certain operations may be performed in a different order, modified, or removed. Moreover, steps may be added to the above described logic and still conform to the described implementations. Further, operations described herein may occur sequentially or certain operations may be processed in parallel. Yet further, operations may be performed by a single processing unit or by distributed processing units. 
       FIG. 4  illustrates one implementation of a computer architecture  400  of the network components such as the storage controllers shown in  FIG. 1 . The architecture  400  may include a processor  402  (e.g., a microprocessor), a memory  404  (e.g., a volatile memory device), and storage  406  (e.g., a non-volatile storage such as magnetic disk drives, optical disk drives, a tape drive, etc.). The storage  406  may comprise an internal storage device or an attached network accessible storage. Programs in the storage  406  are loaded into the memory  404  and executed by the processor  402  in a manner known in the art. The architecture further includes a network card  408  to enable communication with a network. An input device  410  is used to provide user input to the processor  402  and may include a keyboard, mouse, pen-stylus, microphone, touch sensitive display screen, or any other activation or input mechanism known in the art. An output device  412  is capable of rendering information transmitted from the processor  402  or other component such as a display monitor, printer, storage, etc. 
     The foregoing description of various implementations of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive, nor to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. It is intended that the scope of the invention be limited not by this detailed description, but rather by the claims appended hereto. The above specification, examples and data provide a complete description of the manufacture and use of the composition of the invention. Since many embodiments of the invention can be made without departing from the spirit and scope of the invention, the invention resides in the claims hereinafter appended. 
     The objects of the invention have been fully realized through the embodiments disclosed herein. Those skilled in the art will appreciate that the various aspects of the invention may be achieved through different embodiments without departing from the essential function of the invention. The particular embodiments are illustrative and not meant to limit the scope of the invention as set forth in the following claims.