Patent Publication Number: US-7721057-B2

Title: Method and system for transporting data content on a storage area network

Description:
RELATED APPLICATION 
   This application is a continuation of prior U.S. patent application Ser. No. 10/903,278, entitled “Method and System for Transporting Data Content on a Storage Area Network,” filed Jul. 30, 2004, which is a continuation of prior U.S. patent application Ser. No. 10/072,126, entitled “Method and System for Transporting Data Content on a Storage Area Network,” filed Feb. 7, 2002, which are both hereby incorporated herein by reference in their entirety. 

   FIELD OF THE INVENTION 
   The present invention relates to storage area networks (SANs) and more specifically to the transfer of information from one host computer system to another host computer system in a SAN. 
   BACKGROUND OF THE INVENTION 
   System Area Networks (SANs) provide significant benefits as compared to other network configurations. Typical SANs are highly localized having multiple server or host computer systems communicating with each other and sharing one or more storage subsystems and possibly tape, optical or other backup media changers. Additionally, many SANs have multiple host computer systems that may be used to perform several different but complimentary functions. For example, one host computer system may be used for end-user applications while a second host computer system may be used to perform background, administration type functions such as backing up end-user application data or other system data or for performing extended query resolution on large databases of information. Using two host computer systems in such a manner significantly improves the performance of the system since the two may operate substantially in parallel. 
   One issue that arises when configuring a SAN to utilize two or more host computer systems to operate in parallel relates to the sharing of the data used by each host computer system. That is, the end-user host computer system may require access to a specific volume of information stored either locally on its own computer system or on a storage subsystem that is connected to the SAN. The storage subsystem may have an extensive amount of storage capabilities and may in fact provide storage for many other host computer systems in the SAN. Additionally however, the specific volume requested by the first host computer system may also be needed by the second host computer system in order to perform its functions. Such conflicts typically need to be resolved in order for both host computer systems to access the information and to operate in a more optimal manner. 
   Of particular concern is the case where the second computer system requires a relatively exact, read-only copy of all the data on a volume of information. A volume relates to portions of memory that have been logically combined and presented to a host computer system such that the host computer system views the volume as one portion of memory, e.g., a single disk or a single drive of information. 
   One solution to this problem involves the first computer system sending all the information, over the network, to the second computer system. Unfortunately however, this method significantly saturates the network and reduces the performance of the network and is therefore unsatisfactory. 
   A second solution to transferring information relates to the use of a “point-in-time copy” of the data, also referred to as “shadow copies” or “snapshots.” Point-in-time copies are physical copies of data that are created by a storage subsystem. In essence, there are quite of few storage systems that have the capability of quickly and efficiently creating a “mirror” or a point-in-time copy of a portion of the physical storage in their respective systems. The point-in-time copy, therefore, relates to a full physical copy of information stored in another portion of the storage subsystem. Since the point-in-time copy is stored in another portion of the storage subsystem, the second computer system may be provided direct access, without conflict, to the point-in-time copy. Providing access of the point-in-time copy to the second computer system is referred to as transferring ownership of the data from the first computer system to the other computer system, i.e., transporting the content to the second machine. 
   Creation of a point-in-time copy is done by a storage subsystem, which is typically controlled by a hardware provider. Unfortunately however, hardware providers generally operate at the “LUN” level. A LUN is a Logical Unit Number and relates to a virtual device that is “surfaced” by the storage subsystem. A LUN may correspond to a spindle in the storage subsystem or a set of spindles. From the perspective of the host or host computer system accessing a LUN, the LUN looks like a disk which can be used to construct volumes. Hence, volumes are typically a subset of a LUN, but often, a volume may be spread over various LUNs. 
   Hardware surfaced point-in-time copies (i.e., copies created with the help of a hardware subsystem) results in the creation of a new LUN for each original LUN of the volume. The new LUN may be a new, full physical copy or may be an existing copy created using copy-on-write technology. Unfortunately however, transportation of data content typically occurs at the LUN level, not at the volume level. That is, although a LUN may be transported separately from the original LUN to a different machine, there is a considerable amount of work that must be done by a receiving computer system to understand what portions of the LUN are relevant, where those items are located, etc. 
   A common requirement for both these scenarios is to capture what the application data is (i.e., the databases, files, etc.) as well as capture the physical representation of the volumes on which that data resides (i.e., the LUNs). The LUNs and the application data (i.e., how the data is mapped onto the LUNs) need to be surfaced on the machine to which the data is transported. Unfortunately however, hardware mechanisms for creating point-in-time copies operate on the LUN level and therefore there is no way to access data based on volumes that may be spread across several LUNs. Additionally, within a SAN environment, there may be multiple storage subsystems that may be capable of creating point-in-time copies wherein each subsystem is made by different vendors. Unfortunately, in such an environment, each requestor or importer must be aware of specific hardware components for these subsystems in order to import a point-in-time copy. 
   It is with respect to these and other considerations that the present invention has been made. 
   SUMMARY OF THE INVENTION 
   The present invention relates to a system and method of transporting volumes of information from one host computer system to another using point-in-time copies of LUNs but wherein the hardware provider does not necessarily understand the volume configuration of the data. Indeed, the present invention relates to an intermediate layer, i.e., a point-in-time copy interface layer that communicates with both a requesting host computer system and a hardware provider to enable the transfer of volumes of information without requiring that the hardware provider understand the volume information. 
   In accordance with particular aspects, the present invention relates to a system having a storage subsystem module that stores data for at least one host computer system and wherein the data is generally stored in one or more LUNs. Additionally, the system has a requestor module, such a host computer system, for requesting the transportation of data stored in the storage subsystem, the transportation involving the transfer of information from a first host computer system to a second host computer system. The requesting module requests the transportation of volume of information stored on a portion of one or more LUNs. The system also has a point-in-time copy interface module for receiving the request and generating an instruction to create a point-in-time copy, wherein the instruction comprises identification information related to LUNs having portions of the volume to be copied. A provider module is also part of the system and it receives the instruction to create a point-in-time copy of the LUNs and creates the point-in-time copy of those LUNs. The provider module also provides mapping information to the point-in-time copy interface relating to location information for the point-in-time copy. Moreover, the point-in-time copy interface may further generate a backup components document describing the volume to be transported such that an importer module for importing the backup components document, and using the information in the backup components document can then access the point-in-time copy of the volume to be transported. 
   In accordance with other aspects, the present invention relates to a method of transporting data from a sending host computer system to a receiving host computer system, wherein the data is stored on volume of information. The method involves creating a point-in-time copy of the volume; generating a backup components document, wherein the document includes location information for point-in-time copy; importing the backup components document to the receiving host computer system; and accessing the point-in-time copy using information in the backup components document. 
   In another embodiment, the method relates to creating a point-in-time copy of each LUN having a portion of the volume to transported; marking portions of the LUN to identify the portions as being associated with the volume to be transported; and then hiding portions of the LUN not associated with the volume to be transported. In accordance with other aspects, the marking act marks the portions of the LUN associated with the volume and in other embodiment the marking act marks portions of the LUN that are not associated with the volume. In yet another embodiment, the method relates to transporting data in a plurality of volumes and the backup component document includes information to describe the plurality of volumes. The backup components document may be an XML document. 
   The invention may be implemented as a computer process, a computing system or as an article of manufacture such as a computer program product. The computer program product may be a computer storage medium readable by a computer system and encoding a computer program of instructions for executing a computer process. The computer program product may also be a propagated signal on a carrier readable by a computing system and encoding a computer program of instructions for executing a computer process. 
   A more complete appreciation of the present invention and its improvements can be obtained by reference to the accompanying drawings, which are briefly summarized below, to the following detail description of presently preferred embodiments of the invention, and to the appended claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  illustrates a system area network that incorporates aspects of the present invention. 
       FIG. 2  illustrates a computer system that may be used according to particular aspects of the present invention. 
       FIG. 3  is a block diagram illustrating functional components of the system area network shown in  FIG. 1  and incorporating aspects of the present invention. 
       FIG. 4  illustrates a logical depiction of a volume spread across multiple LUNs and a point in time copy of the volume. 
       FIG. 5  illustrates a high-level flow chart of functional operations related to the creation of a point-in-time copy that may be transported according to aspects of the present invention. 
       FIG. 6  illustrates a more-detailed flow chart of functional operations related to the actual creation of a point-in-time copy of a set of volumes in accordance with a particular embodiment of the present invention. 
       FIG. 7  illustrates a high-level flow chart of operational characteristics of the present invention with respect to transporting data content from one system to another. 
       FIG. 8  illustrates a more-detailed flow chart of operational characteristics of a particular embodiment of the present invention with respect to transporting data content from one system to another. 
       FIG. 9  illustrates a flow chart of operational characteristics of the act of matching discovered LUNs with point-in-time copy set LUNs, where the matching act is shown and described in conjunction with  FIG. 8 . 
       FIG. 10  illustrates a flow chart of operational characteristics of the present invention with respect to deleting a point-in-time copy of a volume, the volume being part of a point-in-time copy set. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   A distributed environment  100  incorporating aspects of the present invention is shown in  FIG. 1 . The environment  100  has at least one host computer system  102  and potentially other host computer systems such as  104 . The environment  100  may further include an archival backup system  106  for backing up data from either the host computer system  102  or  104 , as described below. Additionally, the environment may include a memory or storage subsystem, such as RAID (Redundant Array of Independent Disks) system  108 . The host computer systems such as  102  and  104 , communicate with the memory system  108  and each other over a network configuration such as SAN  110 . SAN  110  may be a system area network, such as FiberChannel, InfiniBand, among others, that provides communication capabilities to the various components, such as host systems  102  and  104 . Additionally, the SAN may provide communication support with the memory system  108  through a hardware interface  112  shown in  FIG. 1 . In other embodiments, environment  100  may further include many other components, such as other host computer systems, other memory subsystems, an I/O controller to provide an interface connection to other networks, such as the Internet, among others. 
   As stated, the memory system  108  stores information for use by one of the host computer systems  102  and  104 . The memory system  108  may be any of a number of different types of memory systems. The hardware interface  112  is typically part of the memory system  108  but may be separate. The hardware interface  112  typically includes the controls for creating and maintaining a point-in-time copy of a logical unit of memory, i.e., a LUN, such as LUNs  114 . Additionally, the hardware interface typically communicates with the host computer systems  102  and  104  over network  110  and is able to provide mapping information for stored data on the various LUNs. Importantly, the subsystem  108  provides the capability to create a point-in-time copy of information at the LUN level, i.e., the system can create a point-in-time copy of a LUN. The subsystem  108  may use mirror technology to create and/or maintain a point-in time copy or the system  108  may work in conjunction with the hardware interface  112  and/or the host computer systems  102  and  104  to create the point-in-time copy upon request using other technology. 
   In an embodiment, at least one of the host computers  102  or  104  communicates with the hardware interface  112  and provides the ability to combine portions or extents of separate LUNs into volumes. Additionally, the computer system  102  may map more than one complete volume to a single LUN. Therefore, applications running on the host computer systems may operate based on volumes of information, which may be larger or smaller than the particular LUN for the given memory system  108 . 
   In essence, one of the host computer systems, such as system  102  requests the creation and/or transportation of one or more volumes of information. Once requested, another process within the same computer system, or potentially a process within another host computer system, determines which LUNs need to be copied and which portions of those LUNs need to be transported or surfaced on the receiving system, such as system  104 . Using this information, the memory system  108  is instructed as to which LUN(s) to copy. Upon receiving the copies of the LUN(s), the necessary portions of the various LUN(s) are combined with reconstruction mapping information as well as any other information that the receiving system requires in order to use the copy of the volume. Once surfaced on the second computer system  104 , system  104  can use the point-in-time copy to perform backups, query resolution or substantially any other function that requires a copy of a volume of information. 
   As an example, an application operating on a first host computer system  102  may request the transfer of its data to another system  104  to be backed up onto archival media  106 . Upon receiving the request, the system  108  creates a point-in-time copy of two LUNs. The volume of information actually required in this example however, only needs portions of each of the two LUNs. The system  108 , only operating at the LUN level, provides copies of both LUNs to the requesting system. The requesting system packages the two LUNs for transport by creating a self-contained description of the application data including where that data resides, how that data is to be restored, and the description of what physical resources need to be brought on line to get to the application data. 
   The receiving system  104  receives the self-contained description and is able to reconstruct all the elements of the volume including the mapping from the original volume to the copied volume even after the copied volume is transported to another machine. Additionally, only those volume(s) that were requested for transport are surfaced on the receiving machine. For example, suppose several volumes are created on a single LUN and only one of them is requested for copy and transport. Since the entire LUN is copied, the portions that are not part of the volume are marked as hidden such that when the point-in-time copy is imported on the receiving system  104 , only the requested volume is surfaced. The other volumes, although they appear on the LUN, remain hidden. 
   A computer system  200  that may represent one of the host computer systems, such as  102  shown in  FIG. 1 , which communicates with other host computer systems, such as system  104  through the network fabric  110  in accordance with the present invention, is shown in  FIG. 2 . In its most basic configuration, computing system  200  is illustrated in  FIG. 2  by dashed line  206 . The system  200  has at least one processor  202  and a system memory  204 . In other embodiments, the system may have more than one processor. 
   In addition to the components illustrated as  206 , the system  200  may also include additional storage (removable and/or non-removable) including, but not limited to, magnetic or optical disks or tape. Such additional storage is illustrated in  FIG. 2  by removable storage  208  and non-removable storage  210 . Computer storage media includes volatile and nonvolatile, removable and non-removable media implemented in any method or technology for storage of information such as computer readable instructions, data structures, program modules or other data. Memory  204 , removable storage  208  and non-removable storage  210  are all examples of computer storage media. Computer storage media includes, but is not limited to, RAM, ROM, EEPROM, flash memory or other memory technology, CD-ROM, digital versatile disks (DVD) or other optical storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to store the desired information and which can be accessed by system  200 . Any such computer storage media may be part of system  200 . Depending on the configuration and type of computing device, memory  204  may be volatile, non-volatile or some combination of the two. 
   System  200  may also contain communications connection(s)  212  that allow the device to communicate with other devices, such as other the other host computer system  104 , or the RAID System  110  shown in  FIG. 1 . Additionally, system  200  may have input device(s)  214  such as keyboard, mouse, pen, voice input device, touch input device, etc. Output device(s)  216  such as a display, speakers, printer, etc. may also be included. All these devices are well known in the art and need not be discussed at length here. 
   Computer system  200  typically includes at least some form of computer readable media. Computer readable media can be any available media that can be accessed by system  200 . By way of example, and not limitation, computer readable media may comprise computer storage media and communication media. Computer storage media, as described above, includes volatile and nonvolatile, removable and non-removable media implemented in any method or technology for storage of information such as computer readable instructions, data structures, program modules or other data. Communication media typically embodies computer readable instructions, data structures, program modules or other data in a modulated data signal such as a carrier wave or other transport mechanism and includes any information delivery media. The term “modulated data signal” means a signal that has one or more of its characteristics set or changed in such a manner as to encode information in the signal. By way of example, and not limitation, communication media includes wired media such as a wired network or direct-wired connection, and wireless media such as acoustic, RF, infrared and other wireless media. Combinations of any of the above should also be included within the scope of computer readable media. 
     FIG. 3  illustrates a software/hardware environment  300  incorporating aspects of the present invention. The environment  300  includes separate modules that perform functional operations in accordance with those aspects. The modules may be operate solely within one computer system, such as system  200  shown in  FIG. 2  or the modules operates in a distributed manner across more than one computer system. The environment  300  includes a requester module  302  that requests that a point-in-time copy of a volume, e.g., volume  303 , be created. 
   In an embodiment, the requestor module  302  relates to a computer application or process that requests that one or more point-in-time copies to be made of one or more original volumes. In one particular embodiment, the requestor  302  is a backup application program that is used to store a copy of original volumes onto another disk or medium. As shown in  FIG. 3 , the requestor module  302  communicates a request to the point-in-time copy interface  304 . The request may include one volume to copy or the request may include multiple volumes. In one embodiment, the requestor  302  also requests that the copy be made available for transport across the network, yet in other embodiments, the network may automatically prepare the copy for transport. 
   Although described as single request, in a particular embodiment, the requester module  302  may make a first request to establish a set of volumes to be copied. In return the point-in-time copy interface  304  may return a unique identifier, such as a GUID (global unique identifier). The requestor module  302  may then send multiple messages indicating which volumes should be added to the set identified by the GUID. Following the addition of volumes to the set, the requester module  302  initiates the copy process. Typically, the set is fixed at the invocation of copy process, such that new volumes cannot be added later. In a particular embodiment, only 64 volumes may be included in the point-in-time copy set. However, in other embodiments, there are no limits on the number of volumes that may be included in a particular set or the number of copies of an original volume that may be requested. 
   Additionally, the requestor application  302  may include one or more writer modules, such as writer modules  316 . In such an embodiment, the writer module actually interacts with the point-in-time copy interface  304  in order to create a snapshot. The writer is responsible for quiecing writes to a data store used by the requestor  302  for the period of time that the point-in-time copy is actually materialized. In addition, the writer interacts with other requestor modules (not shown) to describe what is to be copied, e.g., backed up, as well as annotate a backup components document to facilitate the restoration of data that is copied. Exemplary writer modules may include a SQL Server Writer. With respect to the SQL Server Writer module, it will cause the storage system to quiesce writes for the period between “freeze” and “thaw”, i.e., the time periods before a point-in-time copy is created and after the point-in-time copy is created, respectively. 
   The request made by requester  302  is conducted to point-in-time copy interface module  304 . In an embodiment, the interface module  304  is on a host computer system, such as system  102  or  104  or distributed throughout the system  100  shown in  FIG. 1 . The point-in-time copy interface module  304  receives the request, parses the request and then instructs a provider  306  to create a point-in time copy. The interface module, in an embodiment, provides a layer of abstraction between the provider  306  and requester  302  such that the provider  306  is not required to understand volumes or other concepts used by the requester  302 . In essence, the point-in-time copy interface intercepts requests from the requestor and instructs the provider accordingly. 
   The point-in-time copy interface layer  304  also constructs a backup metadata document based on information provided by the requestor (and potentially by the writer). As part of the document, the layer  304  includes a point-in-time copy description based on the original set of volumes and information received from a provider  306  as to the set of LUN copies created for each point-in-time volume copy. 
   The provider  306  receives instructions from the point-in-time copy interface  304  to create a point-in-time copy. Upon receipt, the provider  306  communicates with a storage subsystem  308  to actually create a point-in-time copy of at least one LUN. In essence, the storage subsystem  308  may have several physical disks that may be logically divided into separate units, each having a unique number, such as LUNs  310  and  312 . The provider causes the system  308  to create at least one copy of one or more particular LUNs, such as copies  314  and  315 . The provider  306  may describe the mapping between the set of LUNs for each original volume in a point-in-time copy set as well as the copies of the LUNs created for each point-in-time volume copy. Additionally, the provider  306  may further assist in surfacing LUN copies when those copies are transported to another computer system. 
   In a particular embodiment, the provider  306  is a hardware provider consisting of a user-mode component that works in conjunction with a hardware storage adapter or external storage subsystem  308  and intercepts access requests, e.g., I/O requests in hardware. Importantly, the provider  306  controls the subsystem to generate the point-in-time copy of a LUN. Typically, hardware providers implement the at least two interfaces, such as “IVssProviderCreateSnapshotSet” and “IVssHardwareSnapshotProvider” interfaces. The first interface is common to all providers and implements the snapshot state sequencing. The second interface is specific to hardware providers and operates on a LUN abstraction. More details of these and other interfaces that may be implemented, along with methods that may be used in accordance with one embodiment, are detailed in the attached Appendix A. 
   Additionally, providers  306  may be implemented as COM components and called out-of-process by the layer  304 . Providers  306  use provider-specific mechanisms to communicate with the host adapter or external RAID storage subsystem that instantiates the snapshot LUNs. In using the providers  306 , there may be no need for any extra kernel mode components to perform the control of the storage subsystem  308 . 
   Hardware providers  306  may support copy-on-write or plex (full mirror copy) copy techniques. Hardware providers  306  support transportable point-in-time copies to allow movement between different computer systems on the SAN. 
   Prior to the actual copy process, the original LUNs may be accessed by a number of different modules, such as writers  316 , which can read and write information from and to the different LUNs. Writers  316  correspond to other processing modules that may be connected to the network, apart from the requestor  302 . In one embodiment, during the actual copy process the original LUNs  310  and  312  cannot be accessed by the writers  316 . In other embodiments however, the original volumes are always visible to the system and can be written to, yet most writers quiesce writes during the freeze and thaw periods to ensure consistency, although this is not required. The process of synchronizing various read and write access requests is discussed in more detail in the U.S. patent application Ser. No. 09/912,615, filed Jul. 24, 2001, entitled SYSTEM AND METHOD FOR BACKING UP AND RESTORING DATA [docket number MS154762.1/40062.0093-US-01], incorporated herein by reference for all that it discloses and teaches, filed concurrently herewith, and assigned to the Assignee of the present application. 
   Once the copy of the required LUN or LUNs is made, information is provided to the point-in-time copy interface module  304  indicating that the copy has been made as well as other information such as the location or access information for the copies. The module  304  combines the received information with mapping and other application data prior to transporting the information to a second computer system. In essence, the module  304  combines LUN information, along with any mapping information to create a volume, such as volume  318 , which represents a copy of the requested volume  303 . The volume  318  is then “surfaced” on an importer module  320 . 
   The importer module  320  relates to computer process or application that resides, at least in part, on a computer system apart from the computer system housing the requester module  302 . Thus, the information has been effectively transported from one machine housing the requestor  302  to a different machine, housing the importer module  320 . Once imported, the importer may reconstruct the volume and perform backup or other functions using the imported volume  318 . Although the volume is considered to be transported, the actual physical information may remain on the storage subsystem  308 , such that the “transportation” process merely involves passing location, access, and ownership information and capabilities from one computer system to another. Once transported, the importer module may access and use the information in the transported volume to perform required functions, such as backup or query process functions. 
   In one embodiment, the point-in-time copy interface  304  uses separate modules to perform various tasks. For instance a receive module  322  may be used to receive the request from the requester  302 . Additionally, the receive module  322  may perform other functions such as general communication between the interface  304  and the requestor  302  or the importer module  320  or the various writers  316 . 
   The interface layer  304  may further include an import parse module  324  for parsing a request. The act of parsing a request may determine whether the request is for creating a point-in-time copy, importing a point-in-time copy, among others. The parse module  324 , in an embodiment works in conjunction with a mapping module  326  to determine and maintain information related to volumes and how the volumes are mapped to separate LUNs located on the storage subsystem. The mapping module  326  provides the level of abstraction between a requestor  302  and a provider  306  such that the requestor can supply requests with respect to volumes without knowledge of how that information is mapped into the LUNs. Similarly, the mapping module  326  allows the provider  306  to send and receive information based on the LUNs, without knowledge of volumes or how the volumes are mapped into the LUNs. 
   The interface layer  326  may further include a control module  328 . The control module, in an embodiment, controls the interaction between various modules and may further control timing and sequencing of events. For instance, the control module  328  may operate in conjunction with a synchronization module  330  to synchronize memory access requests originating from multiple processes, such as writers  316 , requestor  302  and importer  320 . Synchronizing these requests, and potentially pausing various requests, allows the providers  306  to create point-in-time copies without conflicts or missed updates. 
   An import module  332  may be incorporated into the point-in-time interface  304 . The import module  332  packages information received from the providers relating to the location of a physical copy on storage subsystem  308 . Using this information, the import module generates a self-contained description of the information to be surfaced on the importer  320 , as well as any other information such as where the information resides, what other processes should be activated in order to access the information, etc. Typically, the import module  332  may be located on a separate computer system from the requestor module  302 , e.g., the requestor module may be located on the host computer system  102  ( FIG. 1 ) and the import module  332  may be located on the host computer system  104  ( FIG. 1 ). However, in alternative embodiments, the import module  332  may be located on the same computer system as the requestor module  302 , e.g., both modules  302  and  332  may be located on system  102  or system  104  ( FIG. 1 ). 
   Using these modules essentially two primary functions are performed by layer  304 . First, the function of constructing the point-in-time copy and mapping LUN information needed for importing the point-in-time to another machine is performed. Typically this is done on the host machine where the original volumes reside since the mapping is created when the original volumes are snapshotted. Second, the import module  332 , takes in this description and interacts with the provider to expose the point-in-time copy LUNS that correspond to the volumes on the original LUNS. 
   In alternative embodiments, the interface  304  has many other modules, such as a module (not shown) that specifically provides communication control between the providers  306  and the other modules of the interface  304 , for example. 
   As described above, a volume may be wholly located on a single LUN, or on a portion of LUN, or on portions of several LUNs.  FIG. 4  illustrates the concept of spreading an original volume  400  across several LUNs  402 ,  404 , and  406 . In the example shown in  FIG. 4 , original volume  400  relates to a logical unit of memory as viewed by a host computer system, such as system  102  shown in  FIG. 1 . The host computer system  102  may or may not understand the mapping of original volume  400  across the several LUNs. In many cases, the host computer system understands LUNs and volumes but the applications running on the host computer system typically do not understand or operate in terms of LUNs. Instead the applications operate on files in a file system that is implemented on top of a volume (which may be composed of portions of one or more LUNS), i.e., a portion of continuous memory space known as volume  400 . The interface layer  304  ( FIGS. 1 and 3  respectively) provides mapping functions to spread the volume across the various LUNs. 
     FIG. 4  also illustrates a point-in-time copy of LUNs  402 ,  404  and  406 , that is, copies  408 ,  410  and  412 . The copies  408 ,  410 , and  412  are actual physical copies of the various LUNs on the subsystem  308 . In an embodiment, there is a copy of each LUN on the subsystem, but in other embodiments, only a predetermined number or set of LUNs are copied at a time. Maintaining mapping information from the original LUN and how it relates to the various LUNs  402 ,  404 , and  406  provides the ability to reconstruct or generate a copy of original volume  400 , i.e., copy  414 . The copy of the original volume  414  is effectively surfaced on a second computer system, such as system  104  shown in  FIG. 1 . 
   The LUNs, such as LUN  1   402 , LUN  2   404  and LUN N  406  exemplify the numerous LUNs present on a storage subsystem. Each LUN comprises multiple portions or extents, such as portions  416 ,  418  and  420 . Of course, there may be many other portions included in a particular LUN. When copies of the LUNs  402 ,  404  and  406  are created, all the portions of the LUN are copied into the point-in-time copy. Sometimes, portions of a LUN are copied but are not necessarily part of the original volume  400  and are therefore not part of the copy of the original volume  414 . 
   As an example, assume that volume  400  is mapped to the three volumes  402 ,  404  and  406 . However, in this example volume  400  does not include portions  418  on LUN  1   402  or portion  422  on LUN N  406 . When a point-in-time copy is created, all portions of each LUN is copied, including portions  418  and  422 , which correspond to portions  424  and  426  on copies  408  and  412 , respectively. However, prior to creating the point-in-time copy, the portions  418  and  422  are marked to indicate that these portions should be excluded from the copy of the original volume  414 . The actual markings on  418  and  422  are represented by marks  427  and  429 . Following the actual point-in-time copy process, since the process copies the LUNs relatively exactly, the markings  427  and  429  appear on the extents  424  and  426  of LUN copies  408  and  412 . The actual markings on  424  and  426  are represented by marks  428  and  430 . The markings  428  and  430  provide the necessary information to indicate that these extents  424  and  426  should be hidden or removed from the copy of the original volume  414 . The types of markings may vary, but the interface layer, such as layer  304  shown in  FIG. 3  recognizes the markings so as to exclude the portions. 
   In an embodiment, the provider  306  in conjunction with the subsystem  308  provides the state necessary to support not only the access to volumes on point-in-time copy but also the tagging or marking of a portion of a LUN as read-only and/or hidden. The state is on the hardware LUN and travels with the LUN. Moreover, the state is preserved across boot epochs and/or device discovery. In a particular embodiment, the layer  304  manages the state of these read-only or hidden portions. 
     FIG. 5  illustrates the functional components related to requesting and creating a transportable volume or set of volumes. Flow  500  generally relates to the process performed by the layer  304  shown in  FIG. 3 . Flow  500  begins as receive operation  502  receives a request for a point-in-time copy of a volume for transport. As discussed above, a requester module, such as module  302  shown in  FIG. 3 , may generate the point-in-time copy request and send the request to the layer  304 . The request may include a single volume or multiple volumes in a set. The request may further include an indication that the new point-in-time copy should be transportable, such as by including a “transportable” attribute. Additionally, the request may comprise a plurality of communications, such as a request to begin adding volumes to a set, adding those volumes to the set, and then submitting the set to be copied. 
   Once receive operation  502  receives the request to create a point-in-time copy for a volume or a set of volumes, resolve operation  504  resolves mapping of volume information into LUN information. In the case where multiple volumes are being copied, in an embodiment, the resolve operation  504  may begin resolving volume/LUN mapping information as it receives each volume, without waiting for the remaining volumes. In alternative embodiments however, resolve operation may wait until all volumes have been requested. 
   Resolve operation  504  determines which LUNs are required to be copied. In an embodiment, the resolve operation may communicate with the one or more providers  306  to determine whether the requested LUNs are supported, and which provider supports those particular LUNs. With respect to hardware providers, the provider is presented with the information about the set of LUNs used to construct the volume and the hardware provider returns an indication as to whether the volume is supported or not by indicating whether those LUNs are supported. This determination should be all or nothing, i.e., if one LUN is not supported then the volume cannot be copied. Also, in an embodiment, the same hardware provider must support all LUNs contributing to a specific volume. In this embodiment, the hardware provider may also augment any LUN information that may be useful to either the requestor or the interface layer, such as layer  304 . For example, the LUN information may be augmented with an interconnect address or the like. 
   Following the resolution of volume and LUN information operation  504 , synchronize operation  506  communicates with various other writers, if there are any, that a point-in-time copy is going to be created. Synchronize operation may simply instruct other writers to stop writing and wait a predetermined time period to allow existing access requests to complete before proceeding. In other embodiments, other methods may be used to effectively communicate with the writers such that the writers do not attempt to access or modify a volume of information while a copy is being made. Preventing access during the actual copy process eliminates issues of missed updates or inaccurate point-in-time copy information. 
   Additionally, during the synchronize writers operation  506 , an indication may be sent to a provider that a point-in-time is going to be requested. That is, the hardware provider supporting the LUNs of the volume to be copied is notified that a copy of the volume is to be made and which LUNs should be copied. However, the notification indicating an upcoming point-in-time copy operation allows the provider time to prepare for the actual point-in-time copy process. 
   Following synchronize operation  506 , mark operation  508  marks, in one embodiment, all volumes on all LUNs that are being copied as hidden and read only. In alternative embodiments, portions of original LUNs that are not associated with requested volumes may be uniquely marked. The hardware provider exposes marking capability relating to read-only or hidden portions of LUNs. Using this capability, mark operation marks unassociated LUNs as hidden. In other embodiments, other methods may be used to identify those portions of LUN copies that are not associated with a volume to be transported. In some cases, however, a requested volume may be placed entirely on one or more LUNs such that each portion of each LUN copy is associated with a copied volume. In such a case, mark operation  508  may not be necessary. That said, however, the mark operation  508  may be necessary for other reasons. For example, the mark operation  508  may be used to mark the point-in-time volumes as read only. Additionally, the import algorithm discussed below in conjunction with  FIG. 8  relies on looking for volumes marked as hidden in order to find the point-in-time volumes such that mark operation  508  may be necessary when implementing such a search algorithm. 
   Mark operation  508  occurs prior to the creation of a point-in-time copy, e.g., operation  510  discussed below. The purpose of this requirement is that most storage subsystems do not allow the marking or modification of a point-in-time copy once it has been created. Thus, the original volumes that are affected are marked as read-only and hidden which will cause all copied volumes that are surfaced on the receiving machine as read-only and hidden. The mark or tag may be implemented using hidden sectors on MBR (Master Boot Record) disks or operating system software specific bits in the partition header entry on GPT (GUID Partition Table) disks. When marking occurs before the creation of the point-in-time copy, then the markings carry over once the copy is made, such that point-in-time copies will include the proper markings. Additionally, an extra step of removing the markings from the original volumes may also be required in this case. 
   Upon completion of mark operation  508 , instruct operation  510  instructs the provider to create the point-in-time copy of the associated LUNs. Essentially, instruct operation  510  relates to the actual creation of the point-in-time copy of the LUNs associated with requested volume. Instruct operation  510  may comprise a series of different acts as discussed below in conjunction with  FIG. 6 . Following instruct operation  510 , the actual point-in-time copies of the associated LUNs exist on the subsystem, such as system  308  shown in  FIG. 3 . 
   Once the instruct or copy operation  510  has completed, obtain and store operation  512  obtains information from the hardware provider relating to the point-in-time copy set, including the copied volumes, LUN mappings and information as to how the volumes are located on the LUNs. The hardware provider is sent information relating to the original volume and requested to construct corresponding information related to the point-in-time copy of the LUNs. Upon obtaining the information, operate and store operation  512  stores the information into a backup components document, such as the sample document shown below in Appendix B. In an embodiment, the document is an XML document containing original LUN information, new point-in-time copy LUN information and identifications for the disk extents for each volume in the point-in-time copy set. The backup components document may then be used at a later time to surface the copied volumes on the second machine. In one embodiment, a surfaced or exposed point-in-time copy is accessible in the Microsoft WINDOWS® operating system namespace via drive letter, mount point, volume device name, and/or network share. 
   With respect to a particular embodiment, in order to keep track of the mapping from the original volume to the point-in-time copy volume, a “SNAPSHOT_SET_DESCRIPTION” XML element appears in the backup components document and describes all properties of a point-in-time copy set (i.e., a set of volumes copied at the same point in time). In particular, it contains information about the physical layout of the original volumes as well as the physical layout of the snapshot volumes. Additionally, the physical layout of the volumes is described in terms of a “LUN_MAPPING” XML element. There is an array of LUN_MAPPING elements for each volume in the point-in-time copy set. The LUN_MAPPING element consists of three components, e.g., a source “LUN_INFORMATION,” target “LUN_INFORMATION,” and a “DISK_EXTENT” array. The source LUN_INFORMATION describes the physical characteristics of the original LUN, the destination LUN_INFORMATION describes the physical characteristics of the destination LUN, and the DISK_EXTENTS describes what contiguous portions of the original LUN are occupied. The LUN_INFORMATION contains enough information to identify the LUN and includes such information as the product id, serial number, vendor identification, as well as addressing information used to find the LUN on the SAN. 
   The SNAPSHOT_SET_DESCRIPTION is built by snapshot service with cooperation from the snapshot provider and is stored in the backup components document. When the requestor (for example the backup application) requests that the point-in-time copy be surfaced on another machine, the SNAPSHOT_SET_DESCRIPTION is extracted from the backup components document and is used to obtain access to the target LUNS as well as reconstruct the mapping from the original volumes to the point-in-time copy volumes that are surfaced. The mapping is generally necessary to find where a corresponding file (as specified in the backup components document) on the original volume is to be found on the point-in-time copy volume. 
   In a particular embodiment, the creation of a point-in-time copy relates to the creation of a point-in-time copy set, which involves copying multiple volumes. Thus, a point-in-time copy set relates to more than one volume of information being copied relatively simultaneously, i.e., each volume copy of the point-in-time set having the same point-in-time characteristic. The layer  304  ( FIG. 3 ) manages the process of creating a point-in-time copy set, the process shown in  FIG. 6 . 
   Initially, flow  600  begins as receive operation  602  receives a request to add a volume to the set of volumes. As discussed above, the requester module, e.g.,  302  ( FIG. 3 ) may request that more than one volume be included in the point-in-time copy process. In one embodiment, the requestor sends a command to the interface layer  304  indicating that a set of volumes are to be copied. In such a case, the requestor then receives multiple requests, each indicating that a new volume is to be added to the set, and which volume to add to the set. Operations  602  through  612 , described below, relate to the acts involved with establishing the set of volumes to be included in the point-in-time copy. 
   Upon receiving a request to add a new volume to the set of volumes  602 , determine operation  604  determines the set of LUNs that are used to compose that new volume. The information may be gleaned from information describing the volume or referenced elsewhere in the system. In an embodiment, the LUNs are determined by calling a module, such as IOCTL_VOLUME_GET_DISK_EXTENTS, which invokes the volume manager to describe which drives are used and which ranges of bytes on each drive are used. There is a one-to-one mapping between physical drives (as seen by the operating system) and LUNs (exposed by the storage subsystem). 
   Next, the first hardware provider is identified at identify operation  606 . Using the LUN identification information determined at operation  604 , the first hardware provider is asked whether that hardware provider supports those LUNs at ask operation  608 . I.e., operation  608  determines whether the identified provider supports the LUNs for the new volume being added to the set of volumes. In an embodiment, the provider is called using “AreLunsSupported” wherein the call includes the set of LUNs. The provider returns an indication as to whether it can create a point-in-time copy for all the LUNs identified in the call. 
   If the provider can create a point-in-time copy of all the LUNs identified in the call, then the provider will return an indication to that effect. In such a case, flow  600  branches YES to instruct operation  610 . Instruct operation  610  instructs the provider to begin preparations for those LUNs to be involved in a point-in-time copy process. In one embodiment, instruct operation  610  calls the provider with “BeginPrepareSnapshot”, wherein the set of LUNs is also provided in the call. It is contemplated that at this point, the hardware provider should begin the process of creating the snapshot or point-in-time copy. In particular, the provider may respond to the call by allocating resources for the point-in-time copy and by doing any work that can be done in advance of point-in-time copy creation. Typically, for a provider that supports mirrors, the provider should create a mirror and begin syncing the mirror, especially if a mirror does not already exist for each LUN. 
   Although it is contemplated that the hardware provider may begin doing work to prepare for the point-in-time, in alternative embodiments, the instruct operation  610  may simply provide an indication that at some point a point-in-time copy process will be conducted and the provider will be involved. Depending on the hardware provider, such an indication may or may not be used to perform any number of activities in order to adequately prepare for the point-in-time copy process. 
   However, if the provider cannot create a point-in-time copy of all the LUNs in the call, then flow  600  branches NO back to identify operation  606  which identifies the next hardware provider. If the next provider can create a point-in-time copy of all the LUNs in the call then flow will branch YES to instruct operation  610 . However, as above, if the next provider cannot support the LUNs, then flow  600  will branch again back to identify operation  606 . In essence, each of the various providers may be called in order to determine which one supports the LUNs associated with the new volume. If no provider is located that can create a snapshot for all the LUNs in a particular volume then that volume is not added to the set. Essentially, if no hardware provider, such as providers  306  ( FIG. 3 ) is found, then a software snapshot provider is used instead. However, since software providers will not support transportable snapshots, the outcome is the same, i.e., if no hardware provider is found, then the point-in-time copy will not be able to be made on that volume. Additionally, the requestor is notified of that the volume has not been added to the set. 
   In one embodiment, a singular provider must support all LUNs in the call in order for the volume to be added to the set. In alternative embodiments however, volumes may be split across different providers. However, it should be noted that such an embodiment requires additional processing to handle the situation where one provider succeeds at one step in the process but another provider fails. The interface layer  304  may communicate with the various providers to handle such a situation. 
   Following instruct operation  610 , determine operation  612  determines whether there is another volume to evaluate. In essence, operations  604  to  610  repeat for each volume that is to be added to the set. When another volume is to be added to the set, flow branches NO back to receive operation  602 . However, when there are no more volumes to be added to the set, then flow branches YES to receive operation  614 . The requester, such as requestor  302  ( FIG. 3 ) may control whether there are more volumes to be added to the set. Hence, when no more volumes are to be added to the set, the requester may send a “close volume set” command or might send a request to create the point-in-time copy. Alternative embodiments may include other means by which to indicate that no more volumes are to be added to the set. 
   Once all the volumes have been added to the snapshot set, then receive operation  614  receives a request to create the point-in-time copy set. In an embodiment, the requestor indicates that the point-in-time copy set should be created. 
   In order to create the point-in-time copy set, each provider participating in the point-in-time copy set is called with a command to end preparations at call operation  616 , such as with an “EndPrepareSnapshots” command. In an embodiment, this command tells the provider that it should be ready to create snapshots for each LUN that it had previously received in a BeginPrepareSnapshot call at a moments notice. If the provider is syncing mirrors, then the mirrors must be completely synced before this call returns. 
   Following call operation  616 , mark operation  618  marks each original volume in the set as hidden and read-only. Similarly, if multiple volumes are on the LUN, then mark operation  620  marks all other volumes as hidden and read only. It is important that the marking process occurs prior to the creation of the actual point-in-time copy since typically, once the point-in-time copy is created, the point-in-time copy LUNs are not visible to the system and cannot be modified. 
   The purpose of steps  618  and  620  relates to the ultimate goal of having the point-in-time copy volumes marked as hidden and read-only. In order to achieve this goal, the process takes advantage of the fact that the point-in-time copy volumes are relatively exact copies of the original volumes at the time that the point-in-time copy is created, including the hidden and read only bits. Thus setting the hidden and read-only bits on the original volumes propagated such a status to the point-in-time copy volumes. In an embodiment, the marking is done using a mechanism called “RevertOnClose.” Using the RevertOnClose mechanism indicates that when the interface layer  304  ( FIG. 3 ) is done with the original volumes, their markings revert to their original state, e.g., visible and not read-only. In addition, if a crash were to occur, the volumes would automatically revert to their original state prior to being marked as hidden and read only. Typically however, the reversion occurs after the point-in-time copy is created so that the original volumes revert to their original state, but the point-in-time copy volumes do not, i.e., they remain hidden and read-only. 
   Following the marking operations  618  and  620 , instruct operation  622  instructs the writers, e.g., writers  316  ( FIG. 3 ) to prepare for the point-in-time copy process. In one embodiment the writers are called with PrepareForSnapshot. Next the instruct operation  624  instructs the writers, e.g., using a “Freeze” command, to stop writing to any volumes on which they have data. Instruct operations  622  and  624  provide the writers with the time to finish writes that have been started and to cache any new writes that are to occur. The communication between the writers and the interface layer  304  ( FIG. 3 ) in this manner results in fewer lost updates and other conflicts. 
   Once all writes are frozen, instruct operation  626  instructs the providers to pre-commit to the upcoming point-in-time copy process. Pre-commit operation  626  essentially relates to a communication between the interface layer  304  and the provider to determine whether the provider is prepared to make the point-in-time copy. In an embodiment, the pre-commit phase may be more complicated. That is, the pre-commit phase, as well as the post-commit phase described below, bracket the creation of the point-in-time copy process, which is typically a very short time frame, e.g., 30 seconds. Bracketing the point-in-time copy process allows the provider time to do any special short term processing either prior to the creation of the point-in-time copy during the pre-commit phase and/or following the creation of the point-in-time copy for post-commit phase. For example, suppose that a provider needs to lock or prevent certain operations, e.g., creation and deletion of LUNs during the short time period that the point-in-time copy is being created. Using the pre-commit and post commit operations, these preparations can be made. Furthermore, the actual time needed for pre-commit and post-commit is often shorter than other preparation time windows, e.g., freezing writes. 
   Next, suspend operation  628  flushes and suspends all writes to all volumes participating in the point-in-time copy set. In an embodiment, a point in time may be chosen after which no further writes will reach each volume until the point-in-time copy is either created or aborted. 
   Following suspend operation  628 , instruct operation  630  instructs the providers to actually make or instantiate the point-in-time copy. This instruction may also be referred to as a “commit” operation and may involve the providers being called with a command “CommitSnapshots.” Instantiating the point-in-time copy may be done in many ways, such as by breaking the plex in a mirror configuration. At this point in time each participating provider must make sure that each point-in-time copy LUN is a relatively exact copy of the original LUN and that no further changes to the original LUN are reflected in the point-in-time copy LUN. 
   Once the point-in-time copy has been created, allow operation  632  allows writes to proceed. In essence, the original volumes may now be modified with the pending writes that were earlier suspended. Since the provider does not allow the modifications to pass through to the point-in-time copy, the system may allow the writes to proceed without concern for the point-in-time copy. 
   Additionally, a post-commit operation  634  may effectively call the providers with a PostCommitSnapshots command. The post-commit command indicates that the point-in-time copy process has been completed. As discussed above with respect to the pre-commit phase, post-commit operation  634  may be more complex and may actually provide time for the providers the time necessary to recover or revert back to the functional level existing prior to the pre-commit phase  626 . 
   Next, thaw operation  636  provides a thaw indication to the writers, such as writers  316  ( FIG. 3 ). The thaw command provides the writers with an indication that new writes may be send to the original volumes. 
   Following operation  636 , which involves the original LUNs, get operation  638  gets information related to the point-in-time copy LUNs. More specifically, each provider may be called with a command “GetTargetLUNs”, wherein the command includes an identification of the original LUNs. In response to this command, the providers return enough information about the point-in-time LUN corresponding to the original LUN so that the point-in-time LUN can be imported onto another system in the SAN and so that the point-in-time LUN can be uniquely identified after it has been imported. In an embodiment, the provider must return enough information in the VDS_LUN_INFORMATION such as serial number, world wide name of the LUN or port, port address on the storage box, and vendor specific information that can be used to uniquely identify the LUN. 
   Following get operation  638 , store operation  640  stores the information about the point-in-time copy, including the mapping from original to target LUNs in the backup components document. The point-in-time copy creation procedure for the provider is complete at this point. If a failure occurs prior to store operation  640 , the provider receives an indication to stop the process, e.g., an AbortSnapshots call, allowing the provider to free up resources that have been allocated for the point-in-time copy. 
     FIG. 7  illustrates the relatively high-level functional components related to importing a point-in-time copy onto another computer system, such as system  104  ( FIG. 1 ). Flow  700  generally relates to the process performed by the point-in-time copy interface layer  304  shown in  FIG. 3  in response to a request to import a specific volume. The request may be made by the import module  320  or by another module indicating that a volume copy should be transported to another system. 
   Flow  700  begins as retrieve operation  702  retrieves the point-in-time copy information from the backup components document. An exemplary backup components XML document is attached as Appendix B. The backup components document provides information to reconstruct the volume on the second machine. In an embodiment, retrieve operation  702  uses the information in the document to construct an array of point-in-time copy LUN information. 
   Once the array of LUN information is constructed, pass operation  704  passes the information to the hardware provider responsible for the point-in-time copy volume. The provider information may also be included in the backup components document. In essence, the provider is called to make the LUNs available at operation  704 . 
   Following the passing of LUN information to the provider, make operation  706  makes the LUNs visible, i.e., available. Typically, make operation  706  is performed by the provider. Making the LUNs available may involve unmasking the LUN at the storage subsystem and, if possible, filter accesses to the machine. Alternatively, the provider may work in conjunction with the interface layer  304  ( FIG. 3 ) to rezone the switches at the network level. 
   Once the LUNs are available, detect operation  708  scans the subsystem for new and available LUNs, i.e., the point-in-time copies of the LUNs. As new LUNs are discovered, information from the backup components document may be used to determine which LUNs are associated with which original volumes, in the case where multiple volumes have been copied. Additionally, this information may be used to determine which portions or extents of each new LUN map to which original volume. 
   Upon discovering all new LUNs, surface operation  710  surfaces the new information on the second machine. In an embodiment, surface operation  710  captures the mapping information between original volumes and the point-in-time copy volumes so that mapping information can later be exposed to applications wanting access to the point-in-time copy. Once the surface operation  710  has captured the mapping information, one or more host computer systems, can be located and mounted as described in more detail with respect to  FIG. 8 . 
     FIG. 8  illustrates a more detailed functional component flow chart related to importing a point-in-time copy onto another computer system, such as system  104  ( FIG. 1 ). Flow  800  is similar to flow  700  in that the a point-in-time copy exists prior to beginning the flow and that the process is generally performed by the point-in-time copy interface layer  304  shown in  FIG. 3  in response to a request to import a specific volume. Flow  800 , however, relates to importing a volume when the volume was originally part of a point-in-time copy set having more than one point-in-time copy volume as well as other details described below. 
   Prior to the beginning of flow  800 , the importer needs the backup components document that was returned when the point-in-time copy set was created in order to import the point-in-time copy set onto a second machine. The backup components document is, in one embodiment, an XML document so it can be transported as a simple text file between machines. The XML document is given to the interface layer  304 , which uses the document to extract the information needed to import the point-in-time copy set. 
   Flow  800  begins with determine operation  802 , which determines the set of point-in-time copy LUNs. That is, the set of point-in-time LUNs is determined using the backup components document. 
   Next, the LUN information for these point-in-time copy LUNs is constructed and the hardware provider that created the point-in-time copy is called, at call operation  804 , with the set of point-in-time copy LUNs that were created by that provider. In an embodiment, the call relates to a “LocateLuns” call and in response to this call, the provider must make all the point-in-time copy LUNs visible to the machine where the point-in-time copy set is being imported. 
   In a particular embodiment, the process of making the LUN visible is done during place operation  806 , which places the LUNs in the same zone as the importer and also unmasks those LUNs at the storage subsystem so that they are visible to the importer system. However, in other embodiments, other methods may be used to make the LUNs visible on the new machine. Also, it should be understood that a single provider may only be able to make a subset of the entire LUN set visible. In this case, only those point-in-time copy volumes that are fully contained on the LUNs that are made visible to the importing machine will be imported. 
   Following place operation  806 , test operation  807  determines whether more providers need to be called. That is, since a point-in-time copy set may involve multiple volumes created by multiple providers, each of the participating providers need to be called with their respective sets of LUN information. Consequently, steps  804 ,  806  and  807  are repeated until all participating providers have been called. 
   Next, detect operation  808  detects any new LUNs. This operation is similar to operation  708  described above in conjunction with  FIG. 7 . In a particular embodiment however, the detect operation involves performing a SCSI rescan in order to determine which new LUNs have been made visible within a zone. 
   Upon detecting a new LUN, the new LUN is matched, at match operation  810  against information identifying point-in-time copy LUNs. In a particular embodiment the process for matching a new LUN with a point-in-time copy LUN is shown and described with respect to  FIG. 9 , discussed below. In essence, each new LUN that has been discovered is matched with identifying information from the backup components documents such that the interface layer not only has access to the LUN but also can map the new LUN to an original LUN. 
   Following match operation  810 , the coordinator, or interface layer, determines at determine operation  812 , which point-in-time copy volumes should be imported based on the set of LUNs found during the detect and match operations  808  and  810 , respectively. That is, assuming all the LUNs for a particular volume are found and matched correctly, then that volume may be imported. If, however, all LUNs for a particular volume are not found, then that volume cannot be imported. 
   Next, check operation  813  checks to see whether there are more LUNs that need to be located. Check operation  813  essentially determines whether other LUNs identified in the Backup Components Document need to be discovered but have yet to be discovered. For each iteration through the loop one or more new LUNs may be discovered. As discussed below with respect to  FIG. 9 , another loop may be used to cycle through and match the various LUNs discovered for each iteration through process steps  804 ,  806  and  807 . Typically, all the LUNs are detected on the first iteration of the loop  804 ,  806  and  807  but, unfortunately limitations of the SCSI rescan operation, e.g., the fact that it is particularly asynchronous, multiple detection operations  804  may be required. 
   If more LUNs need to be discovered then flow branches NO to detect operation  808 . Otherwise flow branches YES to import operation  814 . Alternatively, a timer may be implemented to stop the detection process associated with operation  808 ,  810  and  812  such that following a predetermined time, flow branches to import operation  814  even if some identified LUNs have not been discovered. 
   For each volume that is to be imported, as determined by determine operation  812 , import operation  814  imports the new volume onto the new machine. In operation the import module causes the “volume manager” for that volume to import those volumes onto the machine. The volume manager actually surfaces the volume. That is, in many cases, such as in the case of dynamic volumes which may have multiple LUNs, the volumes are not automatically surfaced when detected by a machine. Instead, the volume either has to have been created on that machine in the first place, or has to be imported onto that machine using a volume manager, which imports the volume. Upon importing volumes to the new machine, the set of volumes on the machine include the point-in-time copy volumes plus potentially other volumes that have were located on the LUNs that contained the point-in-time copy volumes, but were not necessarily included in the point-in-time copy set. It should be understood however, that at this point all the point-in-time copy volumes and the other volumes on the point-in-time LUNs are marked as hidden. 
   Since there may be volumes in the imported data that is not wanted, the next step is to determine which volumes should be unhidden, as opposed to those that should be left hidden. In order to do so, the first step involves identify operation  816 , which identifies the first hidden volume. Identify operation  816  uses the capable of the system to list the set of hidden volumes on the system. Thus, the first hidden volume may be identified. 
   Once identified, determine operation  818  determines the LUNs and portions of those LUNs that the identified volume appears. This information may be gleaned from the volume information itself. That is, using the volume information, appropriate system calls may be made to determine which LUNs the volume appears on and which portions of those LUNs are used by the volume. 
   Using the LUN and portion information related to the volume, compare operation  820  compares the hidden volume information with the backup components document to determine if the hidden volume is one of the point-in-time copy volumes. That is, this information is matched with the information in the backup components document to determine if the hidden volume matches one of the snapshot volumes. 
   If compare operation  820  determines that the volume is one of the point-in-time copy volumes then flow branches YES to capture operation  822  which captures the volume name and associate the volume with the original volume that was used to create the point-in-time copy volume. In addition, operation  822  may further unhide the point-in-time copy volume. 
   Following capture operation  822 , check operation  824  check to see if there are more volumes that need to be captured or evaluated from the hidden volume list. If not, then flow branches YES to end operation  826  which ends flow  800 . If so however, flow branches NO back to identify next hidden volume operation  816 . Similarly, if compare operation  820  determines that the volume is not one of the point-in-time copy volumes, then flow branches to capture operation  822 . In essence, operations  816 ,  818 ,  820  and  824  are repeated until all hidden volumes have been evaluated. 
   In a particular embodiment, upon completion of flow  800 , the system has, for each volume in the point-in-time copy set, the name of the original volume, the machine where the original volume resided when the point-in-time copy was created, and the name of the snapshot volume. Additionally, upon completion of flow  800 , each point-in-time copy volume is marked as visible and read only. Moreover, any other volumes that were brought along with the point-in-time copy volumes because they resided on the point-in-time copy LUNs remain marked as hidden. 
   With this information the requestor can determine how to map from the original volumes in the point-in-time copy set to the point-in-time copy volumes in the point-in-time copy set. For example, suppose that the requestor is a backup application and it was backing up the contents of drive c:\ on the original machine and the point-in-time copy volume materialized as \\?\GLOBALROOT\Device\HarddiskVolume55 on the machine where the import is done. The backup can substitute \\?\GLOBALROOT\Device\Harddisk55\ for c:\ for each file being backed up to extract the corresponding file from the point-in-time copy volume. “GLOBALROOT” is an all caps symbolic link but a case insensitive open would succeed with a lower or mixed case “GlobalRoot.” 
     FIG. 9  illustrates a flow chart of operational characteristics of the act of matching discovered LUNs with point-in-time copy set LUNs, where the matching act is shown and described in conjunction with  FIG. 8 . Initially, determine operation  902  determines initial LUN information using SCSI inquiry commands. Then, for each provider participating in the point-in-time copy set, send operation  904  sends the LUN information determined at operation  902 . Send operation may further call each provider using the “FillInLunInfo” command to determine which provider is responsible for the LUN and to receive other information about the LUN, e.g., information that is not available through the basic SCSI inquiry commands. 
   Following send operation  904 , receive operation receives the additional information about the LUN from one of the providers. That is, once a provider indicates creatorship of the LUN, it fills in the VDS_LUN_INFORMATION and sends it back. Upon receiving the information, each point-in-time copy LUN (as determined by GetTargetLuns when the point-in-time copy was created) is matched, at match operation  908 , against the LUN information for the newly arrived LUN. If the LUN information matches, then it is known that the LUN is an appropriate target LUN. 
   Next, check operation  910  checks to see if there are other new LUNs that have been discovered that need to be evaluated, i.e., whether this is the last LUN. If so, then flow branches YES to end operation  912 . Otherwise flow branches NO back to operation  902  to restart the process of evaluating another LUN against the GetTargetLun list. 
     FIG. 10  illustrates a flow chart of operational characteristics of the process of deleting LUNs in a point-in-time copy set of LUNs. Essentially, in order to improve performance of a system, it becomes important to recover resources, such as LUNs allocated by the storage system for point-in-time copy sets, when those point-in-time copies are no longer needed. The process of deleting a point-in-time copy a single volume involves the process shown in  FIG. 10 . All LUNs discussed with respect to  FIG. 10  are point-in-time copy LUNs. 
   Initially, evaluate operation  1002  evaluates the set of point-in-time copy volumes to determine which volumes will remain in the set following the deletion of the one predetermined volume. In this case the point-in-time copy set includes more than one volume and evaluation step  1002  is used to identify the remaining or other volumes in the set. 
   Upon identifying the remaining volumes, determine operation  1004  determines or compiles a list of LUNs used by the point-in-time copy volume that is about to be deleted. These LUNs may be determined from the volume mapping information or other appropriate system calls. 
   Next, evaluate operation  1006  identifies the first LUN in the list of LUNs used by the point-in-time copy volume that is about to be deleted. Operation  1006  essentially starts a loop that evaluates each LUN in the list to determine whether the LUN can be deleted because no point-in-time copy volume resides on the LUN once the current point-in-time copy volume is deleted. Upon identifying the first or next LUN in the list, determine operation  1008  determines if the first or next LUN is being used by any of the point-in-time copy volumes that will remain following the deletion of the volume as determined above in operation  1002 . 
   If the first or next LUN is not being used by another point-in-time copy volume in the set, then the LUN may be deleted. Free operation  1010  frees or deletes the LUN. In order to free the LUN, a call to the hardware provider may be made, such as with a “OnLunFree” call that specifies the LUN to be freed. Note that when all the point-in-time copy volumes in a point-in-time copy set are deleted, then all the LUNs used by that point-in-time copy set are also freed. 
   Following free operation  1010 , test operation  1012  tests the LUN against the list of LUNs to be evaluated to determine if the LUN is the last LUN in the list. If not, then flow branches back to evaluate operation  1006  where the next LUN in the list is identified and evaluated to see if it can be deleted as before. If the LUN is the last LUN in the list, then flow branches YES to send operation  1014 . 
   Send operation  1014  sends, once all LUNs that can be deleted are freed, a notification to the volume managers for those LUNs that those LUNs have been freed. This allows the volume manager to remove or modify state information about those LUNs. Following send operation  1014 , flow  900  ends at end operation  1016 . 
   Referring back to operation  1008 , if the first or next LUN being evaluated is being used by another volume in the point-in-time copy set, then flow branches YES to operation  1018 . Operation  1018  indicates that the LUN is still in use and should not be freed. Operation  1018  may further provide a message back to the system indicating that the LUN may not be freed, but providing the message may not be necessary in some embodiments. Following operation  1018 , flow branches to test operation  1012 , which as described above tests the LUN against the list of LUNs to be evaluated to determine if the LUN is the last LUN in the list. If not, then flow branches NO back to evaluate operation  1006  where the next LUN in the list is identified and evaluated to see if it can be deleted as before. Otherwise flow branches YES to send operation  1014  as described above. 
   Using the system and method described above, content can be effectively transported from one machine on a SAN to another. Indeed, the above system and method effectively enables a protocol where the point-in-time copy provider, e.g. provider  306  shown in  FIG. 3 , is able to create point-in-time copies using only the physical components it controls (i.e., LUNs) and not having to understand anything about the volumes, file systems, or applications running on those physical components. Moreover, the above system and method provides the ability to describe a LUN in such a way that it can be transported and discovered on the machine to which it is transported without additional processing. The method also allows for combining multiple volumes into a copy set and transporting the set as a group. Further, the receiving machine does not see information on LUNs that are not associated with volume it is receiving. 
   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. 
   APPENDIX A 
   Hardware Provider Interfaces and Methods 
   Introduction 
   The Hardware Point-In-Time Copy or Snapshot Provider interfaces are IVssAdmin, IVssProviderNotifications, IVssProviderCreateSnapshotSet, and IVssHardwareSnapshotProvider.
         IVssAdmin       

   The IVssAdmin interface is implemented by VSS, and manages the list of registered providers. 
   Methods 
   
     
       
         
             
             
             
           
             
                 
                 
             
             
                 
               Name 
               Description 
             
             
                 
                 
             
           
          
             
                 
               QueryProviders 
               Queries all registered providers. 
             
             
                 
               RegisterProvider 
               Registers a new snapshot provider. 
             
             
                 
               UnregisterProvider 
               Unregisters an existing provider. 
             
             
                 
                 
             
          
         
       
     
       
       
         
           IVssProviderNotification 
         
       
     
  
   Snapshot providers can be frequently loaded and unloaded. To detect this, providers can provide an optional Notification Interface IVssProviderNotifications. Implementation is optional; providers only need to implement this interface if it is useful for them to catch these events. 
   The IVssProviderNotifications interface is implemented by the provider and is used by VSS to notify the provider about specific events. Every provider must support this interface. This interface must be accessible using IVssHardwareSnapshotProvider::QueryInterface. 
   Methods 
   
     
       
         
             
             
             
           
             
                 
                 
             
             
                 
               Name 
               Description 
             
             
                 
                 
             
           
          
             
                 
               OnLoad 
               Called by VSS to notify the provider that it was 
             
             
                 
                 
               just loaded. 
             
             
                 
               OnUnload 
               Called by VSS to notify the provider that it will be 
             
             
                 
                 
               unloaded. 
             
             
                 
                 
             
          
         
       
     
       
       
         
           IVssProviderCreateSnapshotSet 
         
       
     
  
   The IVssProviderCreateSnapshotSet interface contains the methods during snapshot creation. 
   All providers must support this interface; the interface is common to software and hardware providers. 
   Methods 
   
     
       
         
             
             
           
             
                 
             
             
               Name 
               Description 
             
             
                 
             
           
          
             
               EndPrepareSnapshots 
               Ensure all LUNs in the snapshot set are prepared 
             
             
               PreCommitSnapshots 
               Ensure that the provider is ready to quickly 
             
             
                 
               commit the prepared LUNs. This happens 
             
             
                 
               immediately before the Flush-and-hold writes, but 
             
             
                 
               while applications are in their frozen states. 
             
             
               CommitSnapshots 
               Quickly commit all LUNs in this provider. 
             
             
                 
               Special restrictions exist on what operations 
             
             
                 
               the Provider may perform during this call. 
             
             
               PostCommitSnapshots 
               Called after all the snapshots have been 
             
             
                 
               committed. This happens immediately after the 
             
             
                 
               release-writes to the I/O subsystem, but while 
             
             
                 
               applications are in still in their frozen states. 
             
             
               AbortSnapshots 
               Ends the prepared snapshots in this provider. This 
             
             
                 
               includes all non-committed snapshots and any 
             
             
                 
               pre-committed ones. 
             
             
                 
             
          
         
       
     
       
       
         
           IVssHardwareSnapshotProvider 
         
       
     
  
   Each hardware provider must implement the IVssHardwareSnapshotProvider interface. The COM class that implements this interface is specified by the administrator in IVssAdmin::RegisterProvider at registration time. 
   Methods 
   
     
       
         
             
             
           
             
                 
             
             
               Name 
               Description 
             
             
                 
             
           
          
             
               AreLunsSupported 
               Allows VSS to determine if this hardware 
             
             
                 
               provider can snapshot the LUNs that contribute 
             
             
                 
               to a specific original volume. The provider also 
             
             
                 
               updates the 
             
             
                 
               VDS_LUN_INFO structure. 
             
             
               BeginPrepareSnapshot 
               Adds LUNs to the snapshot set. 
             
             
               GetTargetLuns 
               Retrieves the hardware identification information 
             
             
                 
               for each new created LUN 
             
             
               LocateLuns 
               Performs any necessary RAID subsystem 
             
             
                 
               unmasking and/or zoning to allow a snapshot 
             
             
                 
               LUN to be discovered by this machine. 
             
             
               OnLunEmpty 
               Notifies the provider that a LUN that previously 
             
             
                 
               contained snapshot no longer contains data of 
             
             
                 
               interest. 
             
             
                 
             
          
         
       
     
       
       
         
           IVssAdmin: Registration of Snapshot Providers 
         
       
     
  
   A provider registers with VSS via IVssAdmin::RegisterProvider( ): 
                                          STDMETHODIMP IVssAdmin::RegisterProvider(                               IN  VSS_ID   ProviderId,             IN  CLSID   ClassId,             IN  VSS_PWSZ   pwszProviderName,                           IN  VSS_PROVIDER_TYPE eProviderType,                               IN  VSS_PWSZ   pwszProviderVersion,             IN  VSS_ID   ProviderVersionId             )                        
IVssAdmin::UnRegisterProvider( ) deregisters the provider and removes it and any snapshots instantiated by the provider from snapshot management.
 
   The ProviderId is a GUID that uniquely and persistently identifies the Provider. For example the volsnap.sys provider is defined as: 
   const GUID VSS_SWPRV_ProviderId={0xb5946137, 0x7b9f, 0x4925, {0xaf, 0x80, 0x51, 0xab, 0xd6, 0xb, 0x20, 0xd5}}; 
   Once defined, the ProviderId should remain the same; this is true even when the software revision is updated. The only reason for changing a provider GUID is when the provider functionality changes and both providers might reasonably be active on the same system.
         IVssProviderCreateSnapshot: Creating Snapshots       

   The IVssProviderCreateSnapshotSet interface contains the methods used during snapshot creation. All providers must support this interface; the interface is common to software and hardware providers. 
   For all methods, a successful return indicates that processing for any and all LUNs in the snapshot set was successful.
         IVssProviderCreateSnapshot::EndPrepareSnapshots       

   This method will be called once for the complete snapshot set. After this is called, there will be no more BeginPrepareSnapshot calls. This method is intended as a rendezvous where the provider can wait for any snapshot preparation work to complete. 
   
     
       
         
             
             
           
             
                 
                 
             
           
          
             
                 
               HRESULT EndPrepareSnapshots( 
             
             
                 
                 [in]  VSS_ID   SnapshotSetId, 
             
             
                 
               ); 
             
             
                 
                 
             
          
         
       
     
       
       
         
           Parameters
           SnapshotSetId   [in] Snapshot set identifier   
         
           IVssProviderCreateSnapshot::PreCommitSnapshots 
         
       
     
  
   The PreCommitSnapshots method is called prior to snapshot commit. It should be used to prepare all snapshots in this SnapshotSet for committing by the subsequent CommitSnapshots( ) method. While this is called, applications have been frozen (but the I/O subsystem is not yet blocking filesystem I/O) so the provider should attempt to minimize the amount of time spent in this method. 
   
     
       
         
             
             
           
             
                 
                 
             
           
          
             
                 
               HRESULT PreCommitSnapshots( 
             
             
                 
                 [in]  VSS_ID   SnapshotSetId, 
             
             
                 
               ); 
             
             
                 
                 
             
          
         
       
     
       
       
         
           Parameters
           SnapshotSetId   [in] Snapshot set identifier.   
         
           IVssProviderCreateSnapshot::CommitSnapshots 
         
       
     
  
   The CommitSnapshots method is called at the defined instant at which the snapshots should be taken. For each prepared LUN in this snapshot set, the provider shall perform whatever work is appropriate in order to persist the point-in-time LUN contents, While this method is called, both applications and the I/O subsystem are quiesced so the provider must attempt to minimize the amount of time spent in this method. As a general rule, a provider should spend less than 1 second in this method. 
   In addition, since the I/O system is quiesced at this time, the provider shall take great care not to initiate any I/O that may deadlock the system—for example debug/tracing I/O by the method or by any methods it has invoked (Note that VM-oriented file or paging I/O will not be frozen at this time). 
   
     
       
         
             
             
           
             
                 
                 
             
           
          
             
                 
               HRESULT CommitSnapshots( 
             
             
                 
                 [in]  VSS_ID   SnapshotSetId, 
             
             
                 
               ); 
             
             
                 
                 
             
          
         
       
     
       
       
         
           Parameters
           SnapshotSetId   [in] Snapshot set identifier.   
         
           IVssProviderCreateSnapshot::PostCommitSnapshots 
         
       
     
  
   The PostCommitSnapshots method is called after all providers involved in the snapshot set have succeeded with CommitSnapshots, and VSS has released the ‘Lovelace’ lock on the system I/O. Note that applications are still frozen at this time. 
   This method is an opportunity for the provider to provide additional cleanup work after the snapshot commit. Note that lSnapshotCount should not be needed by hardware providers but is necessary for software providers. 
   
     
       
         
             
             
           
             
                 
                 
             
           
          
             
                 
               HRESULT PostCommitSnapshots( 
             
          
         
         
             
             
             
          
             
                 
                 [in]  VSS_ID 
               SnapshotSetId, 
             
             
                 
                 [in]  LONG 
               lSnapshotCount 
             
             
                 
               ); 
             
             
                 
                 
             
          
         
       
     
       
       
         
           Parameters
           SnapshotSetId   [in] Snapshot set identifier.   lSnapshotCount   [in] Count of snapshots in the snapshot set.   
         
           IVssProviderCreateSnapshot::AbortSnapshots 
         
       
     
  
   The AbortSnapshots method aborts prepared snapshots in this provide. This includes all non-committed snapshots and pre-committed ones. 
   
     
       
         
             
             
           
             
                 
                 
             
           
          
             
                 
               HRESULT AbortSnapshots( 
             
             
                 
                 [in]  VSS_ID   SnapshotSetId 
             
             
                 
               ); 
             
             
                 
                 
             
          
         
       
     
       
       
         
           Parameters
           SnapshotSetId   [in] Snapshot set identifier.   
         
           IVssHardwareSnapshotProvider. Managing LUNs and Volumes 
         
       
     
  
   The IVssHardwareSnapshotProvider interface contains the methods used by VSS to map volumes to LUNs, discover LUNs created during the snapshot process, and transport LUNs on a SAN. All hardware providers must support this interface.
         VDS_LUN_INFO       

   VDS_LUN_INFO structure contains all hardware properties that can be used to locate a LUN. 
   VSS initializes the fields from the SCSI Inquiry Data, plus the Inquiry Data Vital Product Data Pages 0x80 and 0x83 for all LUNs that contribute to a snapshots set. The provider initializes any interconnect specific addresses for any such LUNs and/or corrects any omissions. 
   For all LUNs created by committing a snapshot, the provider initializes all fields. This allows the newly created LUNs to be located by Windows software both on the original machine and/or any other machine in a SAN. 
   
     
       
         
             
           
             
                 
             
           
          
             
               typedef struct _VDS_LUN_INFO 
             
             
                  { 
             
             
                  ULONG m_version; 
             
             
                 // The SCSI-2 device type 
             
             
                 BYTE m_DeviceType; 
             
             
                 // The SCSI-2 device type modifier (if any) - this may be zero 
             
             
                 BYTE m_DeviceTypeModifier; 
             
             
                 // Flag indicating whether the device can support multiple 
             
             
                 // outstanding commands. The actual synchronization in this 
             
             
                 // case is the responsibility of the port driver. 
             
             
                 BOOL m_bCommandQueueing; 
             
             
                 // Contains the bus type (as defined above) of the device. It 
             
             
                 // should be used to interpret the raw device properties at 
             
             
                 // the end of this structure (if any) 
             
             
                 VDS_STORAGE_BUS_TYPE BusType; 
             
             
                 // vendor id string. For devices with no such ID 
             
             
                 // this will be zero 
             
             
                 [string] char *m_szVendorId; 
             
             
                 // device&#39;s product id string. For devices with no such ID 
             
             
                 // this will be zero 
             
             
                 [string] char *m_szProductId; 
             
             
                 // zero-terminated ascii string containing the device&#39;s 
             
             
                 // product revision string. For devices with no such string 
             
             
                 // this will be zero 
             
             
                 [string] char *m_szProductRevision; 
             
             
                 // zero-terminated ascii string containing the device&#39;s 
             
             
                 // serial number. For devices with no serial number 
             
             
                 // this will be zero 
             
             
                 [string] char *m_szSerialNumber; 
             
             
                 // device id descriptor 
             
             
                 VDS_STORAGE_DEVICE_ID_DESCRIPTOR 
             
             
                 m_deviceIdDescriptor; 
             
             
                 // number of interconnects 
             
             
                 ULONG cInterconnects; 
             
             
                 // array of interconnects 
             
             
                 [size_is(cInterconnects)] VDS_INTERCONNECT *rgInterconnects; 
             
             
                 } VDS_LUN_INFO; 
             
             
               typedef struct _VDS_INTERCONNECT 
             
             
                 { 
             
             
                 // address type 
             
             
                 VDS_INTERCONNECT_ADDRESS_TYPE m_addressType; 
             
             
                 // port that address refers to 
             
             
                 ULONG m_cbPort; 
             
             
                  // actual address of port 
             
             
                  [size_is(m_cbPort)] BYTE *m_pbport; 
             
             
                  // size of address 
             
             
                 ULONG m_cbAddress; 
             
             
                  // address relative to the port 
             
             
                  [size_is(m_cbAddress)] BYTE *m_pbAddress; 
             
             
                  } VDS_INTERCONNECT; 
             
             
                 
             
             
               Notes: 
             
             
               All disk or LUN identification structures are defined by the Virtual Disk Service (VDS). 
             
             
               The Volume Snapshot Service and Fabric Virtualization Service use these same definitions. 
             
             
               The VDS_STORAGE_DEVICE_ID_DESCRIPTORS directly corresponds to the return from context page 0x83. 
             
             
               VDS_INTERCONNECT_ADDRESS_TYPE is an enumeration of recognized interconnect addressing schemes and includes, but is not limited to, FCFS, FCPH, FCP3, MAC (iSCSI), and SCSI. 
             
          
         
       
     
       
       
         
           IVssHardwareSnapshotProvider::AreLunsSupported 
         
       
     
  
   This method will be called for each snapshot that is added to the snapshot set. Prior to invoking this method, VSS determines the LUNs that contribute to the LUN. 
   For a specific volume, each LUN can contribute only once; a specific LUN may contribute to multiple volumes. VSS does no tracking of LUNs. The same LUN will never appear more than once in a single call, but may reappear on subsequent calls. Consider the case of two snapshot volumes: D: and E:. D: is an extended volume contained on LUNS  1  and  2 . E: is a simple volume contained on LUN  2 . If both volumes are added to the same snapshot set, LUN  2  will appear on subsequent calls. 
   Prior to returning success, the provider updates the VDS_LUN_INFO structure with the LUN interconnect address(es) and any additional information to ensure later recognition of the LUN. Additionally a rgwszDeviceNames parameter is provided to give the device name of the LUN allowing the provider to open the device itself if necessary. 
   
     
       
         
             
           
             
                 
             
           
          
             
               HRESULT AreLunsSupported ( 
             
          
         
         
             
             
             
          
             
                 [in] 
               LONG 
               lLunCount, 
             
             
                 [in] 
               LONG 
               lContext, 
             
          
         
         
             
          
             
                 [in, unique, size_is(lLunCount)] VSS_PWSZ *rgwszDevices, 
             
             
                 [in, out, size_is(lLunCount)] VDS_LUN_INFO *pLunInformation, 
             
          
         
         
             
             
             
          
             
                 [out] 
               BOOL 
               *pbIsSupported 
             
             
               ); 
             
             
                 
             
          
         
       
     
       
       
         
           Parameters
           lLunCount   [in] Number of LUNs contributing to this snapshot volume   pLunInformation   [in, out] Array of VDS_LUN_INFO for each LUN contributing to the snapshot volume.   rgwszdevices.   Array of device names one for each lun. Each device names can be used to open the device using the CreateFile API   
         
           IVssHardwareSnapshotProvider::BeginPrepareSnapshot 
         
       
     
  
   This method will be called for each snapshot that is added to the Snapshot set. 
   
     
       
         
             
           
             
                 
             
           
          
             
               HRESULT BeginPrepareSnapshot( 
             
          
         
         
             
             
          
             
                 [in]  VSS_ID 
               SnapshotSetId, 
             
             
                 [in]  VSS_ID 
               SnapshotId, 
             
             
                 [in]  LONG 
               lLunCount, 
             
             
                 [in]  LONG 
               lContext, 
             
          
         
         
             
          
             
                 [in, unique, size_is(lLunCount)] VSS_PWSZ *rgDeviceNames, 
             
             
                 [in, out, size_is(lLunCount)] VDS_LUN_INFO *rgLunInformation 
             
             
               ); 
             
             
                 
             
          
         
       
     
       
       
         
           Parameters
           SnapshotSetId   [in] Snapshot set identifier.   SnapshotId   [in] Name of the volume the snapshot is to be created on.   lLunCount   [in] Number of LUNs contributing to this snapshot volume   rgLunInformation   [in] Array of VDS_LUN_INFO for each LUN contributing to the snapshot volume   rgwszDeviceNames.   Array of device names one for each lun. Each device names can be used to open the device using the CreateFile API   
         
           IVssHardwareSnapshotProvider::GetTargetLuns 
         
       
     
  
   This method will be called once after PostCommitSnapshots for the complete snapshot set. Identifying information for each newly created LUN is returned to VSS. That information must include not only the device attributes (eg serial number), but also any and all network addresses. 
   
     
       
         
             
           
             
                 
             
           
          
             
               HRESULT GetTargetLuns( 
             
             
                 [in] LONG  lLunCount, 
             
             
                 [in, unique, size_is(lLunCount)] VSS_PWSZ *rgDeviceNames, 
             
             
                 [in, unique, size_is(lLunCount)] VDS_LUN_INFO *rgSourceLuns, 
             
             
                 [in, out, size_is(lLunCount)] VDS_LUN_INFO *rgDestinationLuns 
             
             
               ); 
             
             
                 
             
          
         
       
     
       
       
         
           Parameters
           lLunCount   [in] Number of LUNs contributing to this snapshot volume   rgSourceLuns   [in] Array of VDS_LUN_INFO for each LUN contributing to the snapshot volume snapshot set identifier.   rgDestinationLuns   [out] Array of VDS_LUN_INFO for each new LUN created during snapshot processing. There should be a one-to-one correspondence between each element of rgSourceLuns and rgDestinationLuns.   rgwszDeviceNames.   Array of device names one for each lun. Each device names can be used to open the device using the CreateFile API   
         
           IVssHardwareSnapshotProvider::OnLunEmpty 
         
       
     
  
   This method is called whenever VSS determines that snapshot LUN contains no interesting data. All snapshots have been deleted (which also causes deletion of the volume). The LUN resources may be reclaimed by the provider and reused for another purpose. 
   Note that OnLunEmpty is called on a best effort basis. VSS invokes the method ONLY when the LUN is guaranteed to be empty. There may be many cases where the LUN is empty but VSS is unable to detect this. An example of this case is when a snapshot LUN is moved to a different host but not actually transported or imported by VSS. That LUN appears as any other LUN and volumes can be simply deleted via Disk Management without any notification of VSS. 
   
     
       
         
             
             
           
             
                 
                 
             
           
          
             
                 
               HRESULT OnLunEmpty ( 
             
             
                 
                 [in, unique] VSS_PWSZ *wszDeviceName, 
             
             
                 
                 [in, unique] VDS_LUN_INFO *pInformation 
             
             
                 
               ); 
             
             
                 
                 
             
          
         
       
     
       
       
         
           Parameters
           pInformation   [in] The VDS_LUN_INFO for an empty LUN   wszDeviceName   The name of the device corresponding to the lun being freed up. The device name can be used to open the device using the CreateFile API.   
         
           IVssHardwareSnapshotProvider::LocateLuns 
         
       
     
  
   This method will be called once when a snapshot set is transported between machines. The provider is responsible for any unmasking at the hardware and any necessary switch zoning. VDS_LUN_INFO passed to the provider is exactly that received by VSS at GetTargetLuns. 
   Immediately after this method completes, VSS will perform any host-based unmasking and invoke IOCTL_DISK_FIND_NEW_DEVICES. This causes any exposed LUNs to be discovered by PNP. Note that host-based masking is a post-Whistler feature. 
   
     
       
         
             
             
           
             
                 
                 
             
           
          
             
                 
               HRESULT LocateLuns( 
             
             
                 
                 [in]  LONG  lLunCount, 
             
             
                 
                 [in, unique, size_is(lLunCount)] 
             
             
                 
                   VDS_LUN_INFO *rgSourceLuns); 
             
             
                 
                 
             
          
         
       
     
       
       
         
           IVssHardwareSnapshotProvider::FillInLunInfo 
         
       
     
  
   This method will be called when information is needed about a particular Lun. The provider is responsible for supplying this information. 
   
     
       
         
             
           
             
                 
             
           
          
             
               HRESULT FillInLunInfo( 
             
          
         
         
             
             
          
             
                 [in] 
               VSSPWSZ wszDeviceName, 
             
             
                 [in, out] 
               VDS_LUN_INFO *pLunInfo, 
             
             
                 [out] 
               BOOL *pbIsSupported 
             
          
         
         
             
          
             
                ); 
             
             
                wszDeviceName - name of the device being queried. The device 
             
             
               name can be used to open the device using the CreateFile API, 
             
             
                pLunInfo - lun information for the device. The hardware provider 
             
             
               should fill in any fields in the lun information to uniquely identify the 
             
             
               device in such away that the lun information matches the lun 
             
             
               information for the device as returned in GetTargetLuns.] 
             
             
                pbIsSupported - whether this provider supports the device. 
             
             
                ] 
             
             
                 
             
          
         
       
     
   
   
     
       
         
             
           
             
               APPENDIX B 
             
             
                 
             
             
               EXEMPLARY BACKUP COMPONENTS DOCUMENT 
             
             
                 
             
           
          
             
                 
             
          
         
         
             
          
             
                 -  &lt;Schema name=“VssComponentMetadata” xmlns=“urn:schemas-microsoft-com:xml- 
             
             
                 data” xmlns:dt=“urn:schemas-microsoft-com:datatypes”&gt; 
             
             
                 -  &lt;AttributeType name=“filespec” dt:type=“string” required=“yes”&gt; 
             
             
                  &lt;description&gt;File specification. Can include wildcard characters ? and 
             
             
                   *&lt;/description&gt; 
             
             
                 &lt;/AttributeType&gt; 
             
             
                 -  &lt;AttributeType name=“path” dt:type=“string” required=“yes”&gt; 
             
             
                  &lt;description&gt;Path to a file. The path can include environment variables or 
             
             
                   values extracted from registry keys.&lt;/description&gt; 
             
             
                 &lt;/AttributeType&gt; 
             
             
                 -  &lt;AttributeType name=“recursive” dt:type=“enumeration” dt:values=“yes no” 
             
             
                  default=“no”&gt; 
             
             
                  &lt;description&gt;Is path specified recursive or limited to the directory that is 
             
             
                   specified.&lt;/description&gt; 
             
             
                 &lt;/AttributeType&gt; 
             
             
                 -  &lt;AttributeType name=“alternatePath” dt:type=“string” required=“no”&gt; 
             
             
                  &lt;description&gt;Alternate path in which to find the file. Files in a file group 
             
             
                   may have been copied to an alternative location by the writer. Backup 
             
             
                   should pick up the files from the alternative location instead of the 
             
             
                   original location but should restore the files to their original 
             
             
                   location&lt;/description&gt; 
             
             
                 &lt;/AttributeType&gt; 
             
             
                 -  &lt;AttributeType name=“logicalPath” dt:type=“string” required=“no”&gt; 
             
             
                  &lt;description&gt;Logical path for a database or file group. This logical name 
             
             
                   uses backslash as separators to form a logical namespace 
             
             
                   hierarchy&lt;/description&gt; 
             
             
                 &lt;/AttributeType&gt; 
             
             
                 -  &lt;AttributeType name=“componentName” dt:type=“string” required=“yes”&gt; 
             
             
                  &lt;description&gt;Name used to identify a database or file group. May be 
             
             
                   qualified by a logical path.&lt;/description&gt; 
             
             
                 &lt;/AttributeType&gt; 
             
             
                 -  &lt;AttributeType name=“version” dt:type=“enumeration” dt:values=“1.0” 
             
             
                  required=“yes”&gt; 
             
             
                  &lt;description&gt;Version of a specific document&lt;/description&gt; 
             
             
                 &lt;/AttributeType&gt; 
             
             
                 -  &lt;AttributeType name=“writerId” dt:type=“uuid” required=“yes”&gt; 
             
             
                  &lt;description&gt;Unique id to identify the writer. Note that this identifies the 
             
             
                   writer class rather than a specific instance of the writer.&lt;/description&gt; 
             
             
                 &lt;/AttributeType&gt; 
             
             
                 -  &lt;AttributeType name=“instanceId” dt:type=“uuid” required=“no”&gt; 
             
             
                  &lt;description&gt;Unique id identifying the instance of a writer during backup. 
             
             
                   It has no meaning during restore.&lt;/description&gt; 
             
             
                 &lt;/AttributeType&gt; 
             
             
                 -  &lt;ElementType name=“BACKUP_COMPONENTS” content=“eltOnly” model=“closed” 
             
             
                   order=“many”&gt; 
             
             
                  &lt;description&gt;Components that are backed up or restored. Used to 
             
             
                   communicate between the writer and the backup application during 
             
             
                   backup and restore.&lt;/description&gt; 
             
             
                  -  &lt;AttributeType name=“selectComponents” dt:type=“enumeration” 
             
             
                    dt:values=“yes no” default=“no”&gt; 
             
             
                   &lt;description&gt;Does the backup application select individual 
             
             
                    components or does it backup entire volumes&lt;/description&gt; 
             
             
                  &lt;/AttributeType&gt; 
             
             
                  -  &lt;AttributeType name=“bootableSystemStateBackup” dt:type=“enumeration” 
             
             
                    dt:values=“yes no” default=“no”&gt; 
             
             
                   &lt;description&gt;Is backup saving the bootable state of the 
             
             
                    system.&lt;/description&gt; 
             
             
                  &lt;/AttributeType&gt; 
             
             
                  -  &lt;AttributeType name=“backupType” dt:type=“enumeration” dt:values=“full 
             
             
                    differential incremental log other” required=“yes”&gt; 
             
             
                   &lt;description&gt;Type of backup being performed.&lt;/description&gt; 
             
             
                  &lt;/AttributeType&gt; 
             
             
                  -  &lt;AttributeType name=“partialFileSupport” dt:type=“enumeration” 
             
             
                    dt:values=“yes no” default=“no”&gt; 
             
             
                   &lt;description&gt;Indicates whether the requestor is capable of backing up 
             
             
                    and restoring portions of files. If no, then the writer should never 
             
             
                    generate PARTIAL_FILE or DIRECTED_RESTORE elements. Only 
             
             
                    entire files can be backed up or restored.&lt;/description&gt; 
             
             
                  &lt;/AttributeType&gt; 
             
             
                  &lt;attribute type=“version” /&gt; 
             
             
                  &lt;attribute type=“selectComponents” /&gt; 
             
             
                  &lt;attribute type=“bootableSystemStateBackup” /&gt; 
             
             
                  &lt;attribute type=“backupType” /&gt; 
             
             
                  &lt;attribute type=“partialFileSupport” /&gt; 
             
             
                  &lt;element type=“WRITER_COMPONENTS” /&gt; 
             
             
                   &lt;element type=“SNAPSHOT_SET_DESCRIPTION” minOccurs=“0” 
             
             
                    maxOccurs=“1” /&gt; 
             
             
                 &lt;/ElementType&gt; 
             
             
                 -  &lt;ElementType name=“WRITER_COMPONENTS” content=“eltOnly” model=“closed” 
             
             
                   order=“many”&gt; 
             
             
                  &lt;description&gt;Components that are backed up and restored that are 
             
             
                   associated with a specific writer instance&lt;/description&gt; 
             
             
                  &lt;attribute type=“writerId” /&gt; 
             
             
                  &lt;attribute type=“instanceId” /&gt; 
             
             
                  &lt;element type=“COMPONENT” /&gt; 
             
             
                 &lt;/ElementType&gt; 
             
             
                 -  &lt;ElementType name=“COMPONENT” content=“eltOnly” model=“open” 
             
             
                  order=“many”&gt; 
             
             
                  -  &lt;AttributeType name=“backupSucceeded” dt:type=“enumeration” 
             
             
                    dt:values=“yes no” default=“no”&gt; 
             
             
                   &lt;description&gt;Indication of whether the component was backed up 
             
             
                    successfully or not. This should be set during the BackupComplete 
             
             
                    notification&lt;/description&gt; 
             
             
                  &lt;/AttributeType&gt; 
             
             
                  -  &lt;AttributeType name=“componentType” dt:type=“enumeration” 
             
             
                    dt:values=“database filegroup”&gt; 
             
             
                   &lt;description&gt;Indication of whether component is database or file 
             
             
                    group&lt;/description&gt; 
             
             
                  &lt;/AttributeType&gt; 
             
             
                  -  &lt;AttributeType name=“backupStamp” dt:type=“string” required=“no”&gt; 
             
             
                   &lt;description&gt;This string attribute contains the identifier assigned to 
             
             
                    the backup by the writer. The attribute is set by the writer either 
             
             
                    during the PrepareBackup or PostSnapshot event.&lt;/description&gt; 
             
             
                  &lt;/AttributeType&gt; 
             
             
                  -  &lt;AttributeType name=“previousBackupStamp” dt:type=“string” 
             
             
                    required=“no”&gt; 
             
             
                   &lt;description&gt;In the case of an incremental or differential backup, this 
             
             
                    identifies the backup from which differences are compouted. This 
             
             
                    attribute is set by the requestor prior to the PrepareBackup 
             
             
                    event.&lt;/description&gt; 
             
             
                  &lt;/AttributeType&gt; 
             
             
                  -  &lt;AttributeType name=“selectedForRestore” dt:type=“enumeration” 
             
             
                    dt:values=“yes no” default=“no”&gt; 
             
             
                   &lt;description&gt;This yes/no attribute is set by the request prior to 
             
             
                    calling PreRestore and indicates whether the component is being 
             
             
                    restored or not.&lt;/description&gt; 
             
             
                  &lt;/AttributeType&gt; 
             
             
                  -  &lt;AttributeType name=“additionalRestores” dt:type=“enumeration” 
             
             
                    dt:values=“yes no” default=“no”&gt; 
             
             
                   &lt;description&gt;This yes/no attribute is set by the requestor prior to 
             
             
                    calling PreRestore and indicates whether additional restores of 
             
             
                    the component will follow (i.e., ull restore followed by log 
             
             
                    restores&lt;/description&gt; 
             
             
                  &lt;/AttributeType&gt; 
             
             
                  -  &lt;AttributeType name=“restoreTarget” dt:type=“enumeration” 
             
             
                    dt:values=“original alternate new directed” default=“original”&gt; 
             
             
                   &lt;description&gt;This enumerated attribute is set by the writer during 
             
             
                    PreRestore and indicates whether the files for the component 
             
             
                    should be restored to their original location, alternate location (as 
             
             
                    expressed by ALTERNATE_LOCATION_MAPPING elements in the 
             
             
                    metadata), new location (as expressed by RESTORE_TARGET 
             
             
                    elements created by the writer) or should be partially restored 
             
             
                    (as expressed by the DIRECTED_TARGET element created by the 
             
             
                    writer.&lt;/description&gt; 
             
             
                  &lt;/AttributeType&gt; 
             
             
                  -  &lt;AttributeType name=“preRestoreFailureMsg” dt:type=“string” 
             
             
                    required=“no”&gt; 
             
             
                   &lt;description&gt;This attirbute is set by the writer during the PreRestore 
             
             
                    event if the preRestore operation failed for some reason. It gives 
             
             
                    a textual description of why the preRestore failed.&lt;/description&gt; 
             
             
                  &lt;/AttributeType&gt; 
             
             
                  -  &lt;AttributeType name=“filesRestored” dt:type=“enumeration” dt:values=“none 
             
             
                    all failed” default=“all”&gt; 
             
             
                   &lt;description&gt;This attribute is set by the requestor after restoring files 
             
             
                    for the component (i.e., between the PreRestore and PostRestore 
             
             
                    events). Yes indicates that the files were restored successfully; 
             
             
                    no indicates that the files were not restored and the original files 
             
             
                    are intact; failed indicates that the original files were partially 
             
             
                    overwritten and are therefore corrupt. Note that the failed status 
             
             
                    can only occur in the situation of a restore of a file where only 
             
             
                    part of the data is restored (DIRECTED_RESTORE) or where only 
             
             
                    part of a file is backed up and restored (e.g., as part of a 
             
             
                    differential backup). In these cases a failed restore occurs if some 
             
             
                    of the data to be restored is written to the file but not all. In this 
             
             
                    case, the original copy of the file no long exists and the copy on 
             
             
                    tape is not complete and therefore cannot be used to create a 
             
             
                    consistent copy. The only option is to use a previous full backup 
             
             
                    to restore the data. Note that the “failed” indication can be used 
             
             
                    to indicate that some, but no all of the files of a component were 
             
             
                    restored. The requestore is required to either restore all the files 
             
             
                    of a component or none of the files. However, there are situations 
             
             
                    where this is not possible, and the restoration of a component has 
             
             
                    failed, but cannot be completely undone.&lt;/description&gt; 
             
             
                  &lt;/AttributeType&gt; 
             
             
                  -  &lt;AttributeType name=“postRestoreFailureMsg” dt:type=“string” 
             
             
                    required=“no”&gt; 
             
             
                   &lt;description&gt;This string attribute is set by the writer during the 
             
             
                    PostRestore event. It is a text message indicating why the restore 
             
             
                    failed.&lt;/description&gt; 
             
             
                  &lt;/AttributeType&gt; 
             
             
                  -  &lt;AttributeType name=“backupOptions” dt:type=“string” required=“no”&gt; 
             
             
                   &lt;description&gt;This is a private string passed between the requestor 
             
             
                    and the writer to control the backup of the component. It should 
             
             
                    be set by the requestor prior to the PrepareBackup 
             
             
                    event.&lt;/description&gt; 
             
             
                  &lt;/AttributeType&gt; 
             
             
                  -  &lt;AttributeType name=“restoreOptions” dt:type=“string” required=“no”&gt; 
             
             
                   &lt;description&gt;This is a private string passsed between to requestor 
             
             
                    and the writer to control the restore of a component. It should be 
             
             
                    set by the requestor prior to the PreRestore event.&lt;/description&gt; 
             
             
                  &lt;/AttributeType&gt; 
             
             
                  &lt;attribute type=“componentType” /&gt; 
             
             
                  &lt;attribute type=“logicalPath” /&gt; 
             
             
                  &lt;attribute type=“componentName” /&gt; 
             
             
                  &lt;attribute type=“backupSucceeded” /&gt; 
             
             
                  &lt;attribute type=“backupOptions” /&gt; 
             
             
                  &lt;attribute type=“restoreOptions” /&gt; 
             
             
                  &lt;attribute type=“backupStamp” /&gt; 
             
             
                  &lt;attribute type=“previousBackupStamp” /&gt; 
             
             
                  &lt;attribute type=“selectedForRestore” /&gt; 
             
             
                  &lt;attribute type=“additionalRestores” /&gt; 
             
             
                  &lt;attribute type=“restoreTarget” /&gt; 
             
             
                  &lt;attribute type=“preRestoreFailureMsg” /&gt; 
             
             
                  &lt;attribute type=“filesRestored” /&gt; 
             
             
                  &lt;attribute type=“postRestoreFailureMsg” /&gt; 
             
             
                  &lt;element type=“ALTERNATE_LOCATION_MAPPING” minOccurs=“0” 
             
             
                   maxOccurs=“*” /&gt; 
             
             
                  &lt;element type=“BACKUP_METADATA” minOccurs=“0” maxOccurs=“1” /&gt; 
             
             
                  &lt;element type=“RESTORE_METADATA” minOccurs=“0” maxOccurs=“1” /&gt; 
             
             
                  &lt;element type=“RESTORE_TARGET” minOccurs=“0” maxOccurs=“*” /&gt; 
             
             
                  &lt;element type=“DIRECTED_TARGET” minOccurs=“0” maxOccurs=“*” /&gt; 
             
             
                  &lt;element type=“PARTIAL_FILE” minOccurs=“0” maxOccurs=“*” /&gt; 
             
             
                  &lt;element type=“RESTORE_SUBCOMPONENT” minOccurs=“0” maxOccurs=“*” 
             
             
                   /&gt; 
             
             
                 &lt;/ElementType&gt; 
             
             
                 -  &lt;ElementType name=“ALTERNATE_LOCATION_MAPPING” content=“empty” 
             
             
                  model=“closed”&gt; 
             
             
                 &lt;description&gt;Mapping from a location that was backed up to a location to 
             
             
                   restore to.&lt;/description&gt; 
             
             
                  &lt;attribute type=“path” /&gt; 
             
             
                  &lt;attribute type=“filespec” /&gt; 
             
             
                  &lt;attribute type=“recursive” /&gt; 
             
             
                  &lt;attribute type=“alternatePath” /&gt; 
             
             
                 &lt;/ElementType&gt; 
             
             
                 -  &lt;ElementType name=“BACKUP_METADATA” content=“empty” model=“closed”&gt; 
             
             
                  &lt;description&gt;Default metadata element for backup. Content is a binary hex 
             
             
                   string. Note that the writer can store whatever he wants in the 
             
             
                   component. This is just a simple default mechanism.&lt;/description&gt; 
             
             
                  -  &lt;AttributeType name=“metadata” dt:type=“string” required=“yes”&gt; 
             
             
                   &lt;description&gt;Metadata to be passed on restore&lt;/description&gt; 
             
             
                  &lt;/AttributeType&gt; 
             
             
                  &lt;attribute type=“metadata” /&gt; 
             
             
                 &lt;/ElementType&gt; 
             
             
                 -  &lt;ElementType name=“RESTORE_METADATA” content=“empty” model=“closed”&gt; 
             
             
                  &lt;description&gt;Default metadata element for passing information from the 
             
             
                   writer&#39;s PreRestore event to the writer&#39;s PostRestore event. The data is 
             
             
                   opaque to the requestor.&lt;/description&gt; 
             
             
                  -  &lt;AttributeType name=“metadata” dt:type=“string” required=“yes”&gt; 
             
             
                  &lt;description&gt;Metadata to be passed from PreRestore to 
             
             
                    PostRestore.&lt;/description&gt; 
             
             
                  &lt;/AttributeType&gt; 
             
             
                  &lt;attribute type=“metadata” /&gt; 
             
             
                 &lt;/ElementType&gt; 
             
             
                 -  &lt;ElementType name=“RESTORE_TARGET” content=“empty” model=“closed”&gt; 
             
             
                  &lt;description&gt;This element in a COMPONENT should be supplied if the value 
             
             
                   of the restoreTarget attribute of the COMPONENT is “new”. It supplies 
             
             
                   a mapping from a the original location of the file to the location where 
             
             
                   the file should be restored. There may be multiple RESTORE_TARGET 
             
             
                   elements within a component.&lt;/description&gt; 
             
             
                  &lt;attribute type=“path” /&gt; 
             
             
                  &lt;attribute type=“filespec” /&gt; 
             
             
                  &lt;attribute type=“recursive” /&gt; 
             
             
                  &lt;attribute type=“alternatePath” /&gt; 
             
             
                 &lt;/ElementType&gt; 
             
             
                 -  &lt;ElementType name=“DIRECTED_TARGET” content=“empty” model=“closed”&gt; 
             
             
                  &lt;description&gt;This element in a COMPONENT should be should be supplied if 
             
             
                   the value of the restoreTarget attribute of the COMPONENT is 
             
             
                   “directed”. It is intended to support partial restoration of files or 
             
             
                   potentially how files should be reorganized upon restore. There may be 
             
             
                   multiple DIRECTED_TARGET elements within a 
             
             
                   component.&lt;/description&gt; 
             
             
                  -  &lt;AttributeType name=“targetPath” dt:type=“string” required=“no”&gt; 
             
             
                   &lt;description&gt;This is the target location of the file that is to be written 
             
             
                    by the requestor. If this attribute is not specified then the 
             
             
                    targetPath is assumed to be the same as the original 
             
             
                    path.&lt;/description&gt; 
             
             
                  &lt;/AttributeType&gt; 
             
             
                  -  &lt;AttributeType name=“targetFilespec” dt:type=“string” required=“no”&gt; 
             
             
                   &lt;description&gt;This is the name of the file that is to be written by the 
             
             
                    requestor. If this is not specified then the target filename is 
             
             
                    assumed to be the same as the original file name. Note that if 
             
             
                    both the targetPath and targetFilespec are not specified then the 
             
             
                    original file is overwritten.&lt;/description&gt; 
             
             
                  &lt;/AttributeType&gt; 
             
             
                  -  &lt;AttributeType name=“sourceRanges” dt:type=“string” required=“yes”&gt; 
             
             
                   &lt;description&gt;This is a string of the form (offset:cb ...) where each 
             
             
                    offset is the byte offset to start reading data and cb is the length 
             
             
                    of the data to be read (each is a 64 bit integer). The ranges may 
             
             
                    not overlap and must be monotonically increasing.&lt;/description&gt; 
             
             
                  &lt;/AttributeType&gt; 
             
             
                  -  &lt;AttributeType name=“targetRanges” dt:type=“string” required=“yes”&gt; 
             
             
                   &lt;description&gt;This is a string of the form (offset:cb ...) where each 
             
             
                    offset is the byte offset to start wrting data and cb is the length of 
             
             
                    the data to be written (each is a 64 bit integer). The ranges may 
             
             
                    not overlap and must be monotonically increasing.&lt;/description&gt; 
             
             
                  &lt;/AttributeType&gt; 
             
             
                  &lt;attribute type=“path” /&gt; 
             
             
                  &lt;attribute type=“filespec” /&gt; 
             
             
                  &lt;attribute type=“targetPath” /&gt; 
             
             
                  &lt;attribute type=“targetFilespec” /&gt; 
             
             
                  &lt;attribute type=“sourceRanges” /&gt; 
             
             
                  &lt;attribute type=“targetRanges” /&gt; 
             
             
                 &lt;/ElementType&gt; 
             
             
                 -  &lt;ElementType name=“PARTIAL_FILE” content=“empty” model=“closed”&gt; 
             
             
                  &lt;description&gt;This element in a COMPONENT is supplied by the writer during 
             
             
                   the PostRestore event. It indicates that only a portion of the file should 
             
             
                   be backed up. There may be multiple PARTIAL_FILE elements within a 
             
             
                   single COMPONENT.&lt;/description&gt; 
             
             
                  -  &lt;AttributeType name=“ranges” dt:type=“string” required=“no”&gt; 
             
             
                   &lt;description&gt;This range list has the form (offset:length ...) where 
             
             
                    offset is the byte offset in the file to be backed up and length is 
             
             
                    the length of the data to be backed up. Both are 64 bit integers. 
             
             
                    The ranges must be monotonically increasing and must not 
             
             
                    overlap. If the rangelist is not specified then the entire file should 
             
             
                    be backed up.&lt;/description&gt; 
             
             
                  &lt;/AttributeType&gt; 
             
             
                  -  &lt;AttributeType name=“metadata” dt:type=“string” required=“no”&gt; 
             
             
                   &lt;description&gt;This is metadata used by the writer for restoring the 
             
             
                    partial backup. It might for example, include the total size of the 
             
             
                    file to be restored.&lt;/description&gt; 
             
             
                  &lt;/AttributeType&gt; 
             
             
                  &lt;attribute type=“path” /&gt; 
             
             
                  &lt;attribute type=“filespec” /&gt; 
             
             
                  &lt;attribute type=“ranges” /&gt; 
             
             
                  &lt;attribute type=“metadata” /&gt; 
             
             
                 &lt;/ElementType&gt; 
             
             
                 -  &lt;ElementType name=“RESTORE_SUBCOMPONENT” content=“empty” 
             
             
                  model=“closed”&gt; 
             
             
                  &lt;description&gt;This element in a COMPONENT is added by the requestore 
             
             
                   prior to the PreRestore event. It allows a subcomponent of a backed up 
             
             
                   component to be restored.&lt;/description&gt; 
             
             
                  -  &lt;AttributeType name=“repair” dt:type=“enumeration” dt:values=“yes no” 
             
             
                    default=“no”&gt; 
             
             
                   &lt;description&gt;This indicates that the purpose of the restore is to repair 
             
             
                    one or more files of the component. The writer is responsible for 
             
             
                    identifying what is to be restored using a DIRECTED_TARGET 
             
             
                    element.&lt;/description&gt; 
             
             
                  &lt;/AttributeType&gt; 
             
             
                  &lt;attribute type=“logicalPath” /&gt; 
             
             
                  &lt;attribute type=“componentName” /&gt; 
             
             
                  &lt;attribute type=“repair” /&gt; 
             
             
                 &lt;/ElementType&gt; 
             
             
                 -  &lt;ElementType name=“SNAPSHOT_SET_DESCRIPTION” content=“eltOnly” 
             
             
                  model=“closed”&gt; 
             
             
                  &lt;description&gt;This describes a snapshot, including the snapshot set id as 
             
             
                   well as the volume information for the snapshotted 
             
             
                   volumes&lt;/description&gt; 
             
             
                  -  &lt;AttributeType name=“snapshotSetId” dt:type=“uuid” required=“yes”&gt; 
             
             
                   &lt;description&gt;this is the unique identifier for the 
             
             
                    snapshot&lt;/description&gt; 
             
             
                  &lt;/AttributeType&gt; 
             
             
                  -  &lt;AttributeType name=“context” dt:type=“ui4” required=“yes”&gt; 
             
             
                   &lt;description&gt;this is the context used to create the 
             
             
                    snapshot&lt;/description&gt; 
             
             
                  &lt;/AttributeType&gt; 
             
             
                  -  &lt;AttributeType name=“metadata” dt:type=“string” required=“no”&gt; 
             
             
                   &lt;description&gt;this is private metadata about the snapshot 
             
             
                    set&lt;/description&gt; 
             
             
                  &lt;/AttributeType&gt; 
             
             
                  -  &lt;AttributeType name=“description” dt:type=“string” required=“no”&gt; 
             
             
                   &lt;description&gt;this is a user description of the snapshot&lt;/description&gt; 
             
             
                  &lt;/AttributeType&gt; 
             
             
                  &lt;attribute type=“snapshotSetId” /&gt; 
             
             
                  &lt;attribute type=“context” /&gt; 
             
             
                  &lt;attribute type=“description” /&gt; 
             
             
                  &lt;attribute type=“metadata” /&gt; 
             
             
                  &lt;element type=“SNAPSHOT_DESCRIPTION” minOccurs=“0” maxOccurs=“*” /&gt; 
             
             
                 &lt;/ElementType&gt; 
             
             
                 -  &lt;ElementType name=“SNAPSHOT_DESCRIPTION” content=“eltOnly” 
             
             
                   model=“closed”&gt; 
             
             
                  &lt;description&gt;This is the description of a snapshotted volume&lt;/description&gt; 
             
             
                  -  &lt;AttributeType name=“snapshotId” dt:type=“uuid” required=“yes”&gt; 
             
             
                   &lt;description&gt;This is the unique id of the snapshotted 
             
             
                    volume&lt;/description&gt; 
             
             
                  &lt;/AttributeType&gt; 
             
             
                  -  &lt;AttributeType name=“originatingMachine” dt:type=“string” required=“yes”&gt; 
             
             
                   &lt;description&gt;This is the machine where the original volume was 
             
             
                    snapshotted&lt;/description&gt; 
             
             
                  &lt;/AttributeType&gt; 
             
             
                  -  &lt;AttributeType name=“originalVolumeName” dt:type=“string” required=“yes”&gt; 
             
             
                   &lt;description&gt;This is the original name of the volume.&lt;/description&gt; 
             
             
                  &lt;/AttributeType&gt; 
             
             
                  -  &lt;AttributeType name=“snapshotAttributes” dt:type=“ui4” required=“yes”&gt; 
             
             
                   &lt;description&gt;this describes the actual snapshot attributes (as defined 
             
             
                    in VSS_VOLUME_SNAPSHOT_ATTRIBUTES)&lt;/description&gt; 
             
             
                  &lt;/AttributeType&gt; 
             
             
                  -  &lt;AttributeType name=“deviceName” dt:type=“string” required=“no”&gt; 
             
             
                   &lt;description&gt;This is the internal device name for the snapshotted 
             
             
                    volume. This can be used if the snapshot is not 
             
             
                    exposed.&lt;/description&gt; 
             
             
                  &lt;/AttributeType&gt; 
             
             
                  -  &lt;AttributeType name=“exposedName” dt:type=“string” required=“no”&gt; 
             
             
                   &lt;description&gt;This is the exposed name of the snapshot 
             
             
                    volume&lt;/description&gt; 
             
             
                  &lt;/AttributeType&gt; 
             
             
                  -  &lt;AttributeType name=“exposedPath” dt:type=“string” required=“no”&gt; 
             
             
                   &lt;description&gt;If only a subdirectory is exposed, this is the path to that 
             
             
                    subdirectory.&lt;/description&gt; 
             
             
                  &lt;/AttributeType&gt; 
             
             
                  -  &lt;AttributeType name=“providerId” dt:type=“uuid” required=“yes”&gt; 
             
             
                   &lt;description&gt;This is the provider that surfaced the 
             
             
                    snapshot&lt;/description&gt; 
             
             
                  &lt;/AttributeType&gt; 
             
             
                  -  &lt;AttributeType name=“timestamp” dt:type=“ui8” required=“yes”&gt; 
             
             
                   &lt;description&gt;this is when the snapshot set was created.&lt;/description&gt; 
             
             
                  &lt;/AttributeType&gt; 
             
             
                  &lt;attribute type=“snapshotId” /&gt; 
             
             
                  &lt;attribute type=“providerId” /&gt; 
             
             
                  &lt;attribute type=“snapshotAttributes” /&gt; 
             
             
                  &lt;attribute type=“originatingMachine” /&gt; 
             
             
                  &lt;attribute type=“originalVolumeName” /&gt; 
             
             
                  &lt;attribute type=“timestamp” /&gt; 
             
             
                  &lt;attribute type=“deviceName” /&gt; 
             
             
                  &lt;attribute type=“exposedPath” /&gt; 
             
             
                  &lt;attribute type=“exposedName” /&gt; 
             
             
                  &lt;element type=“LUN_MAPPING” minOccurs=“0” maxOccurs=“*” /&gt; 
             
             
                 &lt;/ElementType&gt; 
             
             
                 -  &lt;ElementType name=“LUN_MAPPING” content=“eltOnly” model=“closed”&gt; 
             
             
                  &lt;description&gt;Actual mapping of source lun to a destination lun&lt;/description&gt; 
             
             
                  &lt;element type=“SOURCE_LUN” minOccurs=“1” maxOccurs=“1” /&gt; 
             
             
                  &lt;element type=“DESTINATION_LUN” minOccurs=“1” maxOccurs=“1” /&gt; 
             
             
                  &lt;element type=“DISK_EXTENT” minOccurs=“1” maxOccurs=“*” /&gt; 
             
             
                 &lt;/ElementType&gt; 
             
             
                 -  &lt;ElementType name=“DISK_EXTENT” content=“empty” model=“closed”&gt; 
             
             
                  &lt;description&gt;A particular disk extent on a LUN&lt;/description&gt; 
             
             
                  -  &lt;AttributeType name=“startingOffset” dt:type=“ui8” required=“yes”&gt; 
             
             
                   &lt;description&gt;starting offset of the extent in sectors&lt;/description&gt; 
             
             
                  &lt;/AttributeType&gt; 
             
             
                  -  &lt;AttributeType name=“extentLength” dt:type=“ui8” required=“yes”&gt; 
             
             
                   &lt;description&gt;length of the extent in sectors&lt;/description&gt; 
             
             
                  &lt;/AttributeType&gt; 
             
             
                  &lt;attribute type=“startingOffset” /&gt; 
             
             
                  &lt;attribute type=“extentLength” /&gt; 
             
             
                 &lt;ElementType&gt; 
             
             
                 -  &lt;ElementType name=“SOURCE_LUN” content=“eltOnly” model=“closed”&gt; 
             
             
                  &lt;description&gt;The information for the lun on the originating 
             
             
                   volume&lt;/description&gt; 
             
             
                  &lt;element type=“LUN_INFORMATION” /&gt; 
             
             
                 &lt;/ElementType&gt; 
             
             
                 -  &lt;ElementType name=“DESTINATION_LUN” content=“eltOnly” model=“closed”&gt; 
             
             
                  &lt;description&gt;The information for the lun on the snapshotted 
             
             
                   volume&lt;/description&gt; 
             
             
                  &lt;element type=“LUN_INFORMATION” /&gt; 
             
             
                 &lt;/ElementType&gt; 
             
             
                 -  &lt;ElementType name=“INTERCONNECT_DESCRIPTION” content=“empty” 
             
             
                   model=“closed”&gt; 
             
             
                  &lt;description&gt;An interconnect address including the address 
             
             
                   type&lt;/description&gt; 
             
             
                  -  &lt;AttributeType name=“interconnectAddressType” dt:type=“enumeration” 
             
             
                   dt:values=“FCFS FCPH FCPH3 MAC” required=“yes”&gt; 
             
             
                   &lt;description&gt;interconnect address type. Describes type of the 
             
             
                    interconnect address stored in the interconnectAddress 
             
             
                    attribute&lt;/description&gt; 
             
             
                  &lt;/AttributeType&gt; 
             
             
                  -  &lt;AttributeType name=“port” dt:type=“string” required=“no”&gt; 
             
             
                   &lt;description&gt;Port through which the interconnect address is referred 
             
             
                    to. Note that the same device may have different interconnect 
             
             
                    addresses through different ports.&lt;/description&gt; 
             
             
                   &lt;/AttributeType&gt; 
             
             
                  -  &lt;AttributeType name=“interconnectAddress” dt:type=“string” required=“yes”&gt; 
             
             
                   &lt;description&gt;World Wide name or other interconnect address of the 
             
             
                   device&lt;/description&gt; 
             
             
                  &lt;/AttributeType&gt; 
             
             
                  &lt;attribute type=“interconnectAddressType” /&gt; 
             
             
                  &lt;attribute type=“port” /&gt; 
             
             
                  &lt;attribute type=“interconnectAddress” /&gt; 
             
             
                 &lt;/ElementType&gt; 
             
             
                 -  &lt;ElementType name=“LUN_INFORMATION” content=“eltOnly” model=“closed”&gt; 
             
             
                  &lt;description&gt;enough of the location and name of the lun to transport it. 
             
             
                   TBD&lt;/description&gt; 
             
             
                  -  &lt;AttributeType name=“busType” dt:type=“enumeration” dt:values=“Scsi Atapi 
             
             
                    Ata 1394 Ssa Fibre Usb RAID” required=“yes”&gt; 
             
             
                   &lt;description&gt;Type of bus that the LUN is attached to&lt;/description&gt; 
             
             
                  &lt;/AttributeType&gt; 
             
             
                  -  &lt;AttributeType name=“deviceType” dt:type=“ui1” required=“yes”&gt; 
             
             
                   &lt;description&gt;SCSI-2 device type&lt;/description&gt; 
             
             
                  &lt;/AttributeType&gt; 
             
             
                  -  &lt;AttributeType name=“deviceTypeModifier” dt:type=“ui1” required=“yes”&gt; 
             
             
                  &lt;description&gt;SCSI-2 device type modifier (if any) - this may be 
             
             
                   &lt;/description&gt; 
             
             
                  &lt;/AttributeType&gt; 
             
             
                  -  &lt;AttributeType name=“commandQueueing” dt:type=“enumeration” 
             
             
                    dt:values=“yes no” default=“no”&gt; 
             
             
                   &lt;description&gt;Flag indicating whether the device can support mulitple 
             
             
                    outstanding commands. The actual synchronization in this case is 
             
             
                    the responsibility of the port driver.&lt;/description&gt; 
             
             
                  &lt;/AttributeType&gt; 
             
             
                  -  &lt;AttributeType name=“vendorId” dt:type=“string” required=“no”&gt; 
             
             
                   &lt;description&gt;Optional string identifying the vendor&lt;/description&gt; 
             
             
                  &lt;/AttributeType&gt; 
             
             
                  -  &lt;AttributeType name=“productId” dt:type=“string” required=“no”&gt; 
             
             
                   &lt;description&gt;Optional string identifying the product&lt;/description&gt; 
             
             
                  &lt;/AttributeType&gt; 
             
             
                  -  &lt;AttributeType name=“productRevision” dt:type=“string” required=“no”&gt; 
             
             
                   &lt;description&gt;Optional product revision information&lt;/description&gt; 
             
             
                  &lt;/AttributeType&gt; 
             
             
                  -  &lt;AttributeType name=“serialNumber” dt:type=“string” required=“no”&gt; 
             
             
                   &lt;description&gt;Optional serial number of the device&lt;/description&gt; 
             
             
                  &lt;/AttributeType&gt; 
             
             
                  -  &lt;AttributeType name=“diskSignature” dt:type=“uuid” required=“yes”&gt; 
             
             
                   &lt;description&gt;Disk signature or GUID. If a signature than all but the 
             
             
                    lower 32 bits of the GUID are 0.&lt;/description&gt; 
             
             
                  &lt;/AttributeType&gt; 
             
             
                  -  &lt;AttributeType name=“deviceIdentification” dt:type=“string” required=“yes”&gt; 
             
             
                   &lt;description&gt;UUENCODED binary for the device identification page as 
             
             
                    defined by the STORAGE_DEVICE_ID_DESCRIPTOR structure. This 
             
             
                    contains the vendor id, EUI-64 id, FC-PH name, and vendor 
             
             
                    specific data.&lt;/description&gt; 
             
             
                  &lt;/AttributeType&gt; 
             
             
                  &lt;element type=“INTERCONNECT_DESCRIPTION” minOccurs=“0” 
             
             
                   maxOccurs=“*” /&gt; 
             
             
                  &lt;attribute type=“deviceType” /&gt; 
             
             
                  &lt;attribute type=“deviceTypeModifier” /&gt; 
             
             
                  &lt;attribute type=“commandQueueing” /&gt; 
             
             
                  &lt;attribute type=“busType” /&gt; 
             
             
                  &lt;attribute type=“vendorId” /&gt; 
             
             
                  &lt;attribute type=“productId” /&gt; 
             
             
                  &lt;attribute type=“productRevision” /&gt; 
             
             
                  &lt;attribute type=“serialNumber” /&gt; 
             
             
                  &lt;attribute type=“diskSignature” /&gt; 
             
             
                  &lt;attribute type=“deviceIdentification” /&gt; 
             
             
                 &lt;/ElementType&gt; 
             
             
                &lt;/Schema&gt;