Abstract:
A mechanism is provided for storing self-defining data and mapping elements with either a fixed set of allowed structures or types or with the structures and types determined by rules. Recovery is enhanced by the use of backward and forward pointers between data and mapping elements for the data elements in the order written by the management algorithm. Recovery is also enhanced by the use of companion pointers with metadata. The companion pointers may include pointers to data or mapping elements that are part of the same structural grouping. The metadata may describe the structural grouping. The metadata may also include pointers to the previous and/or next versions of the same elements. Recovery of the data and/or mapping structures is achieved by the reverse application of the management algorithm.

Description:
CROSS REFERENCE TO PROVISIONAL AND RELATED APPLICATIONS  
       [0001]    This application claims the benefit of the filing date of corresponding U.S. Provisional Patent Application No. ______, entitled “System for providing a policy-based demand and use of functions like virtual volumes, instant copy, RAID, etc.”, filed Jun. 19, 2000. In addition, the present invention is related to applications entitled A SYSTEM TO SUPPORT DYNAMICALLY FLEXIBLE DATA DEFINITIONS AND STORAGE REQUIREMENTS, serial no. ______, Attorney Docket Number 00-059-DSK; EFFECTING INSTANT COPIES IN A DYNAMICALLY MAPPED SYSTEM, serial no. ______, Attorney Docket Number 00-060-DSK; USING CURRENT RECOVERY MECHANISMS TO IMPLEMENT DYNAMIC MAPPING OPERATIONS, serial no. ______, Attorney Docket Number 00-061-DSK; DYNAMICALLY CHANGEABLE VIRTUAL MAPPING SCHEME, serial no. ______, Attorney Docket Number 00-062-DSK; FLOATING VIRTUALIZATION LAYERS, serial no. ______, Attorney Docket Number 00-116-DSK, and SELF-DEFINING DATA UNITS, serial no. ______, Attorney Docket Number 00-117-DSK, which are filed even date hereof, assigned to the same assignee, and incorporated herein by reference.  
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Technical Field  
           [0003]    The present invention relates to an improved data processing system and, in particular, to recovery of virtualization structures. Still more particularly, the present invention provides a method and apparatus for recovery of virtualization mapping structures utilizing multiple techniques simultaneously and in parallel.  
           [0004]    2. Description of Related Art  
           [0005]    Maps are used in a disk controller to convert a host based Logical Unit (LUN) and Logical Block Address (LBA) to a controller based LUN and LBA. A mapping system is necessary for a disk controller to provide features such as virtual volumes, data compression, and snapshot. In fact, maps are used in current controller designs to facilitate the use of Redundant Array of Independent Disk (RAID) devices.  
           [0006]    A problem that arises when using a mapped based architecture is where to store the maps. Current map designs use anywhere from four megabytes for a very simple map to dynamic mapping systems that use twelve megabytes or more. As the sizes of disks increase and the sizes of system configurations increase, it is not inconceivable that these systems will require maps that are several gigabytes in size.  
           [0007]    These large structures make recovery of the data, in the case of a lost or failed virtual map, a time-consuming and complicated process. In addition, some simple and straightforward mapping schemes are vulnerable to loss of data even if only a small portion of the map is corrupted or lost. In some cases, the recovery takes so long that the customer may consider the data lost even if it can eventually be recovered.  
           [0008]    Thus, it would be advantageous to provide a method and apparatus for recovery of dynamic maps and data managed thereby.  
         SUMMARY OF THE INVENTION  
         [0009]    The present invention provides a mechanism for storing self-defining data and mapping elements with either a fixed set of allowed structures or types or with the structures and types determined by rules. Recovery is enhanced by the use of backward and forward pointers between data and mapping elements for the data elements in the order written by the management algorithm. Recovery is also enhanced by the use of companion pointers with metadata. The companion pointers may include pointers to data or mapping elements that are part of the same structural grouping. For example these pointers may point to the elements that make up a redundancy stripe or the elements that make up a mapping sub-tree. The metadata may describe the structural grouping. The metadata may also include pointers to the previous and/or next versions of the same elements. For example, the metadata may include a pointer to the previous older version of a data block or to the location where the next version of the data block will be stored.  
           [0010]    Recovery of data or mapping structures is achieved by reverse application of the management algorithm. For example, if using a log structured file algorithm for storing the elements, then the whole structure may he recovered by reading the log backwards. Recovery is enhanced by the use of multi-processing and by the use of a binary fracturing algorithm. For example, forward and backward pointers may be used and different processors may be assigned to begin recovery at different partitions of the structure, each recovering a part of the whole.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself, however, as well as a preferred mode of use, further objectives and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein:  
         [0012]    [0012]FIG. 1 depicts a pictorial representation of a distributed data processing system in which the present invention may be implemented;  
         [0013]    [0013]FIG. 2 is a block diagram of a storage subsystem in accordance with a preferred embodiment of the present invention;  
         [0014]    [0014]FIG. 3 is a block diagram of a data structure in accordance with a preferred embodiment of the present invention;  
         [0015]    [0015]FIG. 4 illustrates the logic floc for finding a data element to be processed in accordance with a preferred embodiment of the present invention; and  
         [0016]    [0016]FIG. 5 illustrates the logic flow for processing the meta data of a data element in order to rebuild a virtual mapping table in accordance with a preferred embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0017]    With reference now to the figures, FIG. 1 depicts a pictorial representation of a distributed data processing system in which the present invention may be implemented. Distributed data processing system  100  is a network of computers in which the present invention may be implemented. Distributed data processing system  100  contains a network  102 , which is the medium used to provide communications links between various devices and computers connected together within distributed data processing system  100 . Network  102  may include permanent connections, such as wire or fiber optic cables, or temporary connections made through telephone connections.  
         [0018]    In the depicted example, a server  104  is connected to network  102  along with storage subsystem  106 . In addition, clients  108 ,  110 , and  112  also are connected to network  102 . These clients  108 ,  110 , and  112  may be, for example, personal computers or network computers. For purposes of this application, a network computer is any computer, coupled to a network, which receives a program or other application from another computer coupled to the network. In the depicted example, server  104  provides data, such as boot files, operating system images, and applications to clients  108 - 112 . Clients  108 ,  110 , and  112  are clients to server  104 . Distributed data processing system  100  may include additional servers, clients, and other devices not shown. Distributed data processing system  100  may be implemented as one or more of a number of different types of networks, such as, for example, an intranet, a local area network (LAN), or a wide area network (WAN). Network  102  contains various links, such as, for example, fiber optic links, packet switched communication links, enterprise systems connection (ESCON) fibers, small computer system interface (SCSI) cable, wireless communication links. In these examples, storage subsystem  106  may be connected to server  104  using ESCON fibers. FIG. 1 is intended as an example and not as an architectural limitation for the present invention.  
         [0019]    Turning next to FIG. 2, a block diagram of a storage subsystem is depicted in accordance with a preferred embodiment of the present invention. Storage subsystem  200  may be used to implement storage subsystem  106  in FIG. 1. As illustrated in FIG. 2, storage subsystem  200  includes storage devices  202 , interface  204 , interface  206 , cache memory  208 , processors  210 - 224 , and shared memory  226 .  
         [0020]    Interfaces  204  and  206  in storage subsystem  200  provide a communication gateway through which communication between a data processing system and storage subsystem  200  may occur. In this example, interfaces  204  and  206  may be implemented using a number of different mechanisms, such as ESCON cards, SCSI cards, fiber channel interfaces, modems, network interfaces, or a network hub. Although the depicted example illustrates the use of two interface units, any number of interface cards may be used depending on the implementation.  
         [0021]    In this example, storage subsystem  200  is a shared virtual array. Storage subsystem  200  is a virtual storage system in that each physical storage device in storage subsystem  200  may be represented to a data processing system, such as client  104  in FIG. 1, as a number of virtual devices. In this example, storage devices  202  are a set of disk drives set up as a redundant array of independent disks (RAID) system. Of course, other storage devices may be used other than disk drives. For example, optical drives may be used within storage devices  202 . Further, a mixture of different device types may be used, such as, disk drives and tape drives.  
         [0022]    Data being transferred between interfaces  204  and  206  and storage devices  202  are temporarily placed into cache memory  208 . Additionally, cache memory  208  may be accessed by processors  210 - 224 , which are used to handle reading and writing data for storage devices  202 . Shared memory  226  is used by processors  210 - 224  to handle and track the reading and writing of data to storage devices  202 . In particular, processors  210 - 224  are used to execute instructions for routines used in snapshot copy operations.  
         [0023]    The present invention manages virtual storage facilities comprising an organization of computer equipment, for example, a host network, data transfer means, storage controller means and permanent storage means and attachment means connecting these devices together. The data storage facilities also may include management information associated with data units such that the management information provides an inventory of capabilities with upper and lower boundaries that may limit the options available to store the data and still meets a user&#39;s criteria. For purposes of this application, a data unit is a logical entity known to a owning entity that is composed of a number of data elements and meta-data and a data element is a grouping of data bits or bytes that the subsystem chooses to manage as a consistent set. Such management information may be independent of attributes of characteristics of the elements of the physical storage subsystem actually used to store the data objects, but may consist of imputed associations with those attributes through, for example, changeable rule sets, processes or algorithms. These rule sets, processes or algorithms may be changed by user demand or via processes that may monitor data object usage and manipulation. The storage of data objects may be adjusted to comply with modifications in the, for example, rules sets, processes or algorithms.  
         [0024]    With reference to FIG. 3, a block diagram of a data structure is illustrated in accordance with a preferred embodiment of the present invention. Data structure  300  includes data elements D 1   301 , D 2   302 , D 3   303 , D 4   304 , D 5   305 , D 6   306 , and D 7   307 . Each data element includes metadata uniquely associated with the data such that installation management criteria, boundaries, and preferences for each data unit and attributes for the data units are maintained. This metadata may include time sequencing of metadata (time stamp), location of stored data, structure definition pointers including size parameters, pointers to related metadata units, management rules, sequencing rules, and management functions invoked to accomplish management rules.  
         [0025]    The management rules may include performance criteria, reliability criteria, availability criteria, and capacity criteria. The sequencing rules may include logical rules, time rules, and structure rules. Management functions may include RAID, parity, multiple parity, and other known functions that may be invoked to accomplish management rules. Management rules, sequencing rules, and management functions may be stored in the metadata as pointers to the rules or functions.  
         [0026]    Furthermore, each data element may include pointers to the next or previous version in a time sequence. For example, data element D 1   301  includes a pointer to the next version of updated data, D 2   302 . Consequently, data element D 2   302  includes a pointer to the previous version, D 1   301 . Each data element may include pointers to the next or previous data element in a logical sequence, such as a next track in a sequence. For example, data element D 3   303  may include a pointer to D 4   304  as the next track and D 4   304  may include a pointer to D 5   305  as the next track. Conversely, D 5   305  may include a pointer to D 4   304  as the previous data element in the logical sequence and D 4   304  may include a pointer to D 3   303  as the previous data element.  
         [0027]    Data elements D 2   302  and D 4   304  may include metadata to indicate that they are mirrored with pointers to the mirrored copies. Therefore, one can get twice the read performance and improved availability. Data elements D 5   305 , D 6   306 , and D 7   307  may include metadata to indicate that they are part of a RAID stripe and the available read bandwidth is three drives.  
         [0028]    The metadata may be stored separate from the data. Thus, each data element may include a virtual address (VA) pointing to the host view of the stored data. For example, D 1   301  includes VA  311 , D 2   302  includes VA  312 , D 3   303  includes VA  313 , D 4   304  includes VA  314 , D 5   305  includes VA  315 , D 6   306  includes VA  316 , and D 7   307  includes VA  317 .  
         [0029]    The data elements in FIG. 3 may be mapping elements. Mapping elements may include forward and backward pointers to mapping elements. If the mapping tables are lost or corrupted, then the mapping may be recovered by finding one or more of the data elements, rebuilding the mapping by following the all the links to the other data elements, and reestablishing the mapping entries with the virtual address stored in the data element.  
         [0030]    [0030]FIG. 4 illustrates the logic flow for finding a data element to be processed in accordance with a preferred embodiment of the present invention. In this example, the operation begins by either identifying a virtual space for which mapping has been lost (step  420 ) or identifying a physical space not covered by a virtual map (step  430 ). If an anchor point is recorded (step  422 :YES), then the anchor points are processed to the find data elements in a managed order which includes such techniques as, for example: sequential addresses, sorted by address, sorted by query frequency (step  440 ). To enhance recovery for specific virtual LUNs or searching through virtual LUNs, a set of pointers stored, for example in a linked list, is maintained of logical sequence pointers for the data elements used to store the data units of the virtual LUNS. Pointers are kept in safe storage to at least one data element or an associated metadata unit in the linked list. This may be called an anchor point. Then when recovery is needed or enhanced searching is requested, and a request from a server is received for a data unit in that LUN, the recovery or searching may use the pointer in safe storage to locate one element and follow the sequence of pointers to the requested element. Additional anchor points may be stored to improved recovery or searching speed. The order of processing the discovered anchor points may be optimized for the desired recovery, for example, if seeking a specific data unit, the anchor points are sorted by their address, closer to the requested data unit first.  
         [0031]    Then processing is launched for each data element found (step  460 ) as further explained in FIG. 5.  
         [0032]    Returning to step  430  in which a physical space is identified which is not covered by a virtual map, a determination is then made as to whether or not an anchor point exists (step  432 ). If an anchor point does exist (step  432 :YES), then the anchor point is processed to final data elements in a managed order which is sequential and sorted by address an/or sorted by query (step  440 ). If an anchor point does not exist (step  432 :NO), then a data element is found in a physical space. This may be accomplished by a sequential scan or by selecting a random entry or by a binary search (step  450 ) and then processing is launched for each data element found (step  460 ) which is further explained in FIG. 5.  
         [0033]    [0033]FIG. 5 illustrates the logic flow for processing the meta data of a data element in order to rebuild a virtual mapping table in accordance with a preferred embodiment of the present invention. Expanding on FIG. 4, in this example, the operation begins with a data element being added to the processing queue (step  505 ). The discovered data element(s) is/are sorted (step  510 ). Then a determination is made as to whether or not the processing queue is empty (step  511 ). If the processing queue is empty (step  511 :YES), the operation terminates. If the processing queue is not empty (step  511 :NO) then a determination is made as to whether or not the data element has the location of meta data (step  514 ). If the data element has the location of the meta data (step  514 :YES), the associated meta data is retrieved. Then a determination is made as to whether or not the data element is already recovered (step  517 ). If the data element is already recovered (step  517 :YES), then the operation returns to step  511  in which a determination is made as to whether or not the processing queue is empty. Returning to step  517 , if the data element is not already recovered (step  517 :NO), then the management rules and/or links are determined (step  516 ).  
         [0034]    Returning to step  514 , if the data element does not have the location of the meta data (step  514 :NO), then a determination is made as to whether or not the meta data is with the data (step  515 ). If the meta data is not with the data (step  515 :NO), then the determination is made as to whether or not the data element is already covered (step  517 ). If the meta data is with the data (step  515 :YES), then the management rules and/or links are determined (step  516 ). A mapping table or structure with a virtual address is updated (step  518 ). Then a determination is made as to whether or not there are more management rules and/or links in selected order (step  520 ). If there are not anymore management rules and/or links in selected order (step  520 :NO), then the data element is marked as recovered (step  524 ). The operation then returns to the step in which a determination is made as to whether or not the processing queue is empty (step  511 ).  
         [0035]    If there are more management rules and/or links in selected order (step  520 :YES), then a process is initiated to located another data element or elements using the management rules and/or links according to an ordering priority scheme, which may be, for example, sequential, physical address specific, virtual address specific, forward direction specific, backward direction specific or direction specific in both a forward and backward direction (step  522 ). If the meta data or data elements are stored in a sequential table, a process is initiated to locate additional elements by incrementing to the next table entry and initiating a process to locate additional elements by decrementing to the previous table entry. If there are pointers to a previous or next element in a logical sequence, a process is initiated to locate additional elements by following the “next” pointer and initiating a process to locate additional elements using the previous pointer. If there are companion pointers to elements associated in a redundancy group, a process is initiated to locate additional elements using the companion pointer(s). If there is a request from a host server to access a particular addressed data unit, while recovery is needed or in progress, the recovery may be optimized (directed) for recovery of the requested data unit. For example, if the currently dedicated data element in the recovery process has previous and “next” in logical sequence pointers, the pointer may be selected which points to the requested data element and initiate a process to locate additional elements using that pointer. If the currently located data elements are in a sequential table structure and the requested data element also fits within the table structure, a binary search algorithm may be used on the table structure to locate the requested data element.  
         [0036]    If a primary management rule for the location of data elements is a log structured file (LSF) system and the portion of the map is maximized per unit time, then the LSF may be processed in a reverse manner. In this case, the anchor point may have a pointer to the last LSF log entry and each log entry may contain pointers to the previous log entry and to the meta data and/or data elements updated with that log entry.  
         [0037]    The map recovery may then proceed by processing all the data elements associated with the last LSF log entry. Then locating the previous log entry and processing all the data elements associated with the log entry and following this process for each previous log entry. Since the probability of valid mapping to data elements may decrease with the age of the log entry, this should maximize the recovery of the valid map entries.  
         [0038]    A determination is made as to whether the process in step  522  is able to find a data element (step  526 ). If a data element is not found (step  526 :NO), then the operation returns to step  520  to determine whether there are more management rules or links in selected order. If the process did find a data element (step  526 :YES), then the process sends each found data element back through the process (can be parallel execution) (step  528 ) and returns to step  520  to determine whether there are more management rules or links in selected order.  
         [0039]    An example of applying the process described in FIGS. 4 and 5 to the virtual map structure as described in FIG. 3, assume that D 4   304  in FIG. 3 is a found data structure. Also, assuming a full recovery (i.e., not a recovery at a specific requested data element), the process determines that the data element mapping has not been recovered. The process determines that there two management rules associated with D 4   304  in FIG. 3; one is a logical sequence and the other is a mirrored redundancy group. The mapping table is updated with the virtual address (VA)  314  for D 4   304 . A process (P 1 ) is initiated to locate the next data element using the “next” logical sequence pointer. A process (P 2 ) is initiated to locate the previous element using the “prev” logical sequence pointer. A process (P 3 ) is initiated to locate the companion in the mirror using the “prev” redundancy group pointer. D 4   304  is marked as having been recovered which may be indicated in the mapping structure. Process P 1  locates element D 5   305 . Process P 1  determines that element D 5   305  has not been recovered. Process P 1  determines that element D 5   305  has two associated management rules. One is a logical sequence and the other is a redundancy group (RAID). The mapping table is updated with the virtual address (VA)  315  for data element D 5   305 . A process (P 4 ) is initiated to locate the next element in logical sequence. A process (P 5 ) is initiated to locate the previous element in logical sequence. A process (P 6 ) is initiated to locate the companion element in the redundancy group using the “next” redundancy group pointer. D 5   305  is marked as having been recovered. Process P 6  locates element D 4   304  and determines that element D 4   304  has already been recovered and the process ends.  
         [0040]    It is important to note that while the present invention has been described in the context of a fully functioning data processing system, those of ordinary skill in the art will appreciate that the processes of the present invention are capable of being distributed in the form of a computer readable medium of instructions and a variety of forms and that the present invention applies equally regardless of the particular type of signal bearing media actually used to carry out the distribution. Examples of computer readable media include recordable-type media such a floppy disc, a hard disk drive, a RAM, and CD-ROMs and transmission-type media such as digital and analog communications links.  
         [0041]    The description of the present invention has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art. The embodiment was chosen and described in order to best explain the principles of the invention, the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated.