Abstract:
A method, and associated system, for delivering data services such as virtualization to legacy devices. The method involves reserving a metadata region in memory of a storage resource in a storage pool that is controlled by (or is captive to) a data services platform. The metadata region includes a global set containing information used by the data services platform to manage the data services, including virtualization of volumes throughout the storage pool. The method includes locating an available legacy storage device and retrieving element information for the legacy storage device. A volume or virtualized legacy volume is built based on the collected element information, and the global set in the metadata region is update to include volume information for the legacy storage device. The legacy storage device includes memory that stores legacy or user data, but the steps of the method are performed to leave the legacy data unchanged.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates, in general, to data storage devices and their management including virtualization of the devices, and, more particularly, to a method and corresponding system for providing virtualization data services in a data storage system that includes legacy storage devices with data in place or without disrupting user data on such devices. 
   2. Relevant Background 
   An ongoing challenge facing designers and developers of data storage systems is how best to use and integrate existing legacy storage devices with other data storage devices. A legacy storage device is a data storage device that already contains user or application data because it has been used for data storage in the past, such as a host device running an application or as part of an enterprise&#39;s data storage system. Problems arise later when attempts are made to include the legacy device in a larger data storage system that includes a variety of management services. 
   For example, many data storage systems are managed or configured to provide virtualization features. Virtualization allows a set of storage devices to be pooled together with the combined storage space being regarded as addressable main storage by a user of a data storage system into which virtual addresses are mapped. Presently, when a user allows a data storage system access to a legacy storage device by mapping it to a host or storage manager, the legacy storage device does not support a variety of virtualization features such as volume expansion, snapshot, mirroring, and data migration. Placing metadata or information needed to support these virtualization features on the legacy storage device would destroy the user data stored on the device. As a result, it has proven difficult to fully utilized legacy storage devices that are added to a data storage system with the added devices typically not supporting virtualization and appearing as uninitialized devices or disks to a storage processor. 
   In some data storage applications, a storage system may include a “virtualization head” and a set of “captive” storage devices. The storage devices are captive in that they are initially considered raw storage that can be provisioned by the virtualization head. Part of such provisioning that is done by the virtualization head involves the reservation of a configuration metadata region that maintains logs, configuration information, and the like for each storage device in the system, and the data stored in this region on each device facilitates and supports virtualization throughout the raw storage devices. A problem arises because the virtualization head cannot store its configuration metadata region on a legacy device or volume without destroying previously stored user data. 
   Another problem is that the data services provided by a data storage manager or processor often require a logging region, a data service-specific metadata region, and a scratch pad region to effectively carry out data management functions. As with the configuration metadata regions, the data storage manager or processor cannot store these regions or their corresponding data on the legacy device without copying over existing user data on a legacy device. The lack of this data seriously affects the use and integration of legacy storage devices into data storage systems, which often results in the legacy storage devices not being effectively utilized and their storage capacities being unavailable to all users of the data storage system. 
   Hence, there remains a need for a method and system for more effectively integrating legacy storage devices into data storage systems to enable their pooling with other raw storage devices. Such a method and system preferably would be configured to support at least a portion of the virtualization features presently not available with legacy storage devices such as volume expansion, snapshot, mirroring, data migration, and/or other useful virtualization features. 
   SUMMARY OF THE INVENTION 
   The present invention addresses the above and other problems by providing a method and corresponding systems for providing data services including virtualization to legacy storage devices that are added or made available in a storage pool of captive devices. The methods and systems of the invention are adapted to enable generation and management of virtualized volumes for legacy device without destroying user or legacy data stored on the legacy device. 
   More particularly, a method is provided for delivering data services such as virtualization to legacy storage devices. The method involves reserving a configuration metadata region (or MDR) in memory of a storage resource that is provided in a storage pool and that is controlled by (or is captive to) a data services platform or storage controller, i.e., an MDR is provided on all captive storage devices. The MDR includes a global set of data containing information used by the data services platform to manage or provide the data services, including virtualization of volumes throughout the storage pool. The method continues with locating a legacy storage device available for use or inclusion in the storage pool, and then, retrieving element information for the legacy storage device from the MDR on the captive storage device(s). A volume (or virtualized legacy volume (VLV)) is built based on the collected element information. The method then includes updating the global set of data in the MDR to include information on the volume built using the legacy storage device element information. The legacy storage device includes memory that stores legacy or user data, but the steps of the method are performed to leave the legacy data unchanged, with volume information stored in the global set of the MDR. 
   In some embodiments of the invention, the element information collected for the legacy device may include extent and disk information for the legacy device. The building of the VLV may include building a volume tree and marking the volume tree as a VLV (or flagging the tree) to allow the VLV to be treated differently from other volumes in the storage pool by the data services platform (e.g., no MDR is provided on the legacy device). The method may further include providing a snapshot storage device for the built VLV including updating a metadata region of the snapshot device based on the volume information for the legacy storage device. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  illustrates in block form a data storage system according to one embodiment of the present invention showing a data services platform or storage controller configured to provide the data services functions of the invention to legacy storage devices; 
       FIG. 2  illustrates a volume tree for a virtualized legacy volume (VLV) created for a legacy storage device; 
       FIG. 3  illustrates exemplary steps in a process for forming a VLV, such as that shown in  FIG. 2 , according to the invention; 
       FIG. 4  illustrates a volume tree for a VLV with a dynamic COW pool formed according to one embodiment of the invention; 
       FIG. 5  shows a process for creating the VLV shown in  FIG. 4  with the dynamic COW pool being provided on a storage device in the storage resource pool of the data storage system other than the legacy storage device corresponding to the VLV; 
       FIG. 6  illustrates steps and the responsible components of data services platform for deleting a VLV, such as the VLVs shown in  FIGS. 2 and 4 ; 
       FIG. 7  illustrates an embodiment of a process for restoring a previously created VLV; and 
       FIG. 8  shows a representative single device VLV with a symmetric multi-path according to the invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The invention is generally directed to providing a method and system for providing data services such as virtualization to legacy storage devices that contains user or legacy data that is not affected in providing the data services. The inventive method and system provides a data storage system with a data services platform (or storage controller) that manages a storage resource pool of captive storage resources and legacy storage devices. The legacy storage devices are accessible, such as by mapping to a host, but do not as initially provided to the storage resource pool support data services, such as virtualization, controlled by the data services platform because the legacy storage devices do not store or contain metadata used by the data service platform for providing such services to the captive storage resources. According to the invention, the data services platform reserves a configuration metadata region on each of the captive storage resources that contains the definition of the storage system&#39;s virtualized storage devices along with the state information for both logical and physical devices (e.g., 128 MB for each device that is extensible using a page reference scheme). A portion of the configuration metadata region provides a global set of definitions for the data storage system (i.e., the global set), and this region is mirrored across at least a subset of the captive storage resources for redundancy. 
   The following description describes the method and system of the invention for providing enhanced data services for added legacy storage devices in part by storing configuration metadata for the legacy storage devices in the global set of the data storage system (e.g., stored in the global subset of captive storage resources in each of their global set region of the configuration metadata region of memory). The data services platform or storage controller of the invention includes logic or software (e.g., the platform&#39;s configuration management code) is written or adapted to affect the discovery of legacy volumes (or legacy storage devices) such as physically through its driver stacks and/or logically via a scan of the global set configuration metadata region. As will become clear from the following description, the data services platform is also designed to enable the placement of data service specific data regions, logging regions, and scratch pad regions useful for managing the legacy devices on devices other than the legacy device being “virtualized” through the data services platform. To support virtualization and other data services, a virtualized legacy volume (VLV) is created for each legacy storage device in the storage resource pool, and the VLV is a volume that supports data services whose metadata resides on a device other than the legacy device (i.e., in a global set region of a configuration metadata region of a captive storage resource. Significantly, according to the invention, data services are provided to the legacy storage devices via the data service platform and the use of configuration metadata regions in a global set of captive storage resources while leaving the legacy or user data intact on the legacy storage devices and without requiring the user or legacy data to be copied to a virtualized volume. 
   In the following discussion, computer and network devices (or “elements”), such as the software and hardware devices within the system  100 , are described in relation to their function rather than as being limited to particular electronic devices and computer architectures and programming languages. To practice the invention, the computer and network devices or elements may be any devices useful for providing the described functions, including well-known data processing and communication devices and systems, such as application, database, Web, blade, and entry level servers, midframe, midrange, and high-end servers, personal computers and computing devices including mobile computing and electronic devices with processing, memory, and input/output components running code or programs (“applications”, “tasks” within such applications, and “services”) in any useful programming language, and server devices configured to maintain and then transmit digital data over a wired or wireless communications network. 
   Similarly, data storage systems and memory components are described herein generally and are intended to refer to nearly any device and media useful for storing digital data such as disk-based devices, their controllers or control systems, and any associated software. Data, including transmissions to and from the elements of the network  100  and among other components of the network/systems  100 , such as between services, typically is communicated in digital format following standard communication and transfer protocols, such as TCP/IP, HTTP, HTTPS, FTP, SCSI, iSCSI, FC, iFC, and the like, or IP or non-IP wireless communication protocols, such as a FC storage system linked via an Ethernet. The invention is particularly suited for use with enterprise storage systems such as those serviced by storage arrays managed by a storage controller and including a plurality of data storage devices or arrays (e.g., disk devices and the like). For example, but not as a limitation, the invention and its features may readily be implemented in a data services platform (DSP) or storage controller, such as the DSP provided in the Sun Microsystems, Inc. StorEdge™ 6920 product or similar products, and an associated storage resource pool including captive or assigned storage devices and one or more added legacy storage device. However, the concepts of the invention are readily applicable to many other storage systems that utilize a storage controller to manage data services such as virtualization in a pool of storage resources or devices such as standard disk arrays. 
     FIG. 1  illustrates one embodiment of a data storage system  100  according to the invention. As shown, the system  100  includes a data services platform (or storage controller)  110  that is linked (such as via FC protocol or Ethernet) via digital data communications link  130  to a storage resource pool  140 . The storage resource pool  140  may take a number of forms and may be provided in a single array cabinet or in a plurality of cabinets and other devices containing a variety of heterogeneous storage devices or relatively homogeneous storage devices. The storage resource pool  140  includes one or more captive storage resources  150  that may be considered an attached logical unit (ALU) representing a physical device and/or a logical device represented by an identification number or logical unit number (LUN) given to devices connected to a SCSI adapter. Each captive storage resource  150  includes memory  152  storing data  154  and also, significantly, including a configuration metadata region (MDR)  160 . Typically, the MDR  160  is allocated and created when a device is configured as “captive.” 
   The MDR  160  is an area in memory  152  on each captive ALU that contains information (such as volume and global set information) used by the data services platform  110  to provide data services including virtualization in the storage resource pool  140 , e.g., for the captive storage resources  150  and for the legacy storage devices  170 . To this end, the MDR  160  is shown to include volume state manager (VSM) object data  162 , e.g., partition, parent volume, and other information, and a global set (GS) data  166  including virtualized legacy volume (VLV) data  168 . The GS data  166  is an area of the MDR  160  that is global across the pool  140  managed by the data services platform  110 . Unlike the VOD  162  which contains information specific to the ALU  150  on which it resides, the GS  166  contains chassis wide information. For example, the specific information in the VOD  162  may include a definition of ALU usage of virtual volume and state and configuration information for those virtual volumes associated with the ALU. The GS data  166  is replicated across a set of the captive storage resources  150  (i.e., a global set of the ALUs  150  with the global set being a subset of the ALUs  150  chosen for redundancy), and the GS data  166  contains VLV data  168 . The VLV data  168  represents or defines a virtualized volume with a primary component is a device or ALU without volume and other information used by the data services platform  110  to provide virtualization and other data services. 
   Specifically, the storage resource pool  140  is shown to include one or more (such as more than 2 for redundancy purposes) legacy storage devices  170  which are ALUs that do not have a configuration metadata region as provided for the captive resources  150 . Each legacy device  170  includes memory  174  with legacy data or user data  176  that remains intact although the device  170  may be virtualized by the data services platform  110 . The legacy storage device  170  may be considered a direct access volume (DAV), which is a physical LUN (e.g., an ALU) that does not contain the MDR  160  and that contains data  176  in memory  174  that is mapped to one or more hosts (not shown). To practice the invention, the GS  166  in the MDR  160  of captive storage resource  150  is shown to include the VLV data  168  for legacy storage device  170 , and the VLV data  168  may include the DAV information. The provision of the VLV data  168  in the GS  166  on the captive device  150  enables the data services platform  110  to provide virtualization and/or other data services to the legacy storage device  170  by providing a location for persistent storage of state and configuration of the VLV and data services provided for the VLV. 
   The techniques for creating and managing a VLV are discussed in detail below with reference to  FIGS. 2-8 . The VLVs created for the legacy devices  170  can then be accessed through the platform  110  by devices using the storage resource pool  140  for data storage. In addition to virtualization, the platform  110  can provide data service functions such as remote replication and data mirroring that can be applied to these VLVs while preserving the legacy data  176 . A user of the system  100  can use the platform  110  for centralized remote replication or for migration on the attached legacy storage device(s)  170  (such as an external device) to add addition capacity to a pool  140 . 
   The data services platform or storage controller  110  includes a number of functional components that work in conjunction to provide data services to the legacy storage devices  170  (and captive storage resources  150 ). As shown, the data services platform  110  includes one or more management interfaces  112 , which may be implemented with one or more management interface cards (MIC) in some embodiments. The management interface  112  typically includes embedded software that controls the boot of the platform  110  and interacts with the external processors, such as device management software on storage service processors (not shown), that interact with the platform  110 . The platform  110  includes a block virtualization mechanism (BV)  114  that controls building or generating new volumes in the system  100  including building new VLVs for legacy storage devices  170 . A virtualization configuration manager (VCM)  118  is provided to control changes to the volumes in the system  110 . A master virtualization storage processor (MVSP)  120  is provided to function as an interface between a volume state manager database (VSMDB)  126  and ALU information, among other functions. Additionally, the data services functions of the platform or DSP  110  is provided by a volume state manager (VSM)  124  that acts to manage state information for the volume or devices  150 ,  170  in the storage resource pool  140 . 
   The operation of each of the components of DSP  110  are explained in detail with reference to  FIGS. 2-8 , but prior to this discussion, a number of the architectural specifications of one implementation of the invention are provided to better assist one skilled in the art in fully understanding the benefits of the invention. The DSP  110  may be set up to support a particular number of ALUs, such as for example 128 ALUs, that can be designated as VLVs. Each of these VLVs preferably supports (and hence, the VLV data  168  includes any relevant data) the following virtualization features: (a) any volume type using the VLV allows one or more PIT images to be created against them, such as, for example, 8 PITs; (b) data migration with the DSP  110  allowing the data on a VLV to be migrated to a virtual volume that is managed by the DSP  110 ; (c) local mirroring with the DSP  110  allowing a VLV to be defined as any component of a mirror volume (including mirroring from a VLV to another VLV); (d) mirroring a VLV for an internal volume; (e) multi-path management abstraction with the DSP  110  presenting a VLV as a symmetric volume to host ports (see, for example,  FIG. 8 ); and (f) persistent reservation reserve commands supported by the VLVs. 
   In one specific exemplary, but not limiting, embodiment, the VLV data area  168  is a 16 MB area of the 128 MB MDR  160 , which is used to store VLV and DAV objects. In this example, this allows for a total of 4096 objects to be contained in the VLV region  168 . The number of VLVs supported varies based on how many partitions each VLV contains, but a minimum of 128 VLVs can be supported in this example with the maximum number of partitions in each VLV since the VLV region  168  is mirrored across the global set (or GS subset) of captive storage resources  150 . 
   The DSP  110  is configured to not write any non-host write data to the ALUs  170  designated as VLV. In other words, metadata regions  160  are not written to the legacy storage devices  170 , which are designated as VLVs rather than volumes as are captive storage resources  150 . The VLVs among the legacy storage devices  170  do not support extension or stripping data service features. One reason why extension is not supported is that once the VLV is extended the legacy device  170  may contain references to data on other partitions and if the legacy device  170  is removed from the VLV the data may be unusable. The configuration information for VLVs is preferably redundantly stored on storage (such as devices  150 ) managed by the DSP  110  in the MDR GS. The VLVs preferably support reservations and persistent reservations but are not configured for adoption (e.g., to allow a take-ownership command). 
   In some embodiments of the storage system  100 , the only type of volume that may be used for VLV creation is concatenated. Typically, there is at least one initialized captive storage resource  150  with a MDR  160  in the storage resource pool  140  (or 2 captive ALUs  150  if redundancy is desired) before a legacy storage device  170  is added as a VLV. If dynamic COW expansion is supported in the system  100 , the COW data and log resides on one or more of the captive ALUs  150  since the DSP  110  cannot write to the legacy device  170  (e.g., to a MDR on such as device  170 ). Persistent reservation metadata information is stored in the VSMDB  126 . A legacy device  170  that is part of a VLV as indicated in VLV data  168  cannot be re-used for another volume or DAV. Further, it is preferable in most embodiments of the storage system  100  that a host (not shown) is not allowed to access the legacy devices  170  directly after they are added to a VLV. 
   As can be seen from the above description of  FIG. 1 , a significant change to support VLVs in a storage system is the effective handling of non-captive or non-DSP owned ALUs (i.e., ALUs without a MDR). It is preferable that this challenge be approached such that these ALUs or legacy devices are treated as any other ALU in the storage pool operated by a DSP. In a typical existing storage controller, raw devices such as legacy devices are ignored by the storage controller, e.g., by the VCM and MVSP. For example, when a DAV is added to a target service, the MIC may configure the proper iSCSI connections and set up proper mappings. In contrast for VLVs, the inventors recognize that it will be desirable for the VCM (such as VCM  118  of  FIG. 1 ) to treat raw or legacy devices similar to DSP-owned or captive devices  150  and notify the MVSP  120  when there is a change to any legacy device. In some embodiments, this handled by having the VCM  118  create iSCSI or other communication connections between storage processors (SPs) that contain or control raw or legacy devices. This allows the MVSP  120  to treat the legacy devices as any other ALU (but also has the disadvantage of creating connections for devices the MVSP  120  may not need to access). In more preferred embodiments, the MVSP  120  is configured to recognize when a volume being created is a VLV or at start of day when the VSMDB  126  states there are VLVs. The MVSP  120  requests a list of all non-DSP or non-captive devices (i.e., legacy devices  170 ) from the VCM  118 . The MVSP  120  then adds these devices  170  to its in-memory ALU list. The DSP is typically not allowed to write to any device it discovers that does not have an MDR on it that the DSP recognizes as “its own” until configured to do so by an administrator. 
   Another issue with handling of legacy devices  170  that is addressed by the invention is what should the MIC  112  (or user) see once a raw or legacy device  170  is added to a VLV. In some embodiments, a processor where the legacy device  170  is attached would detect that the ALU  170  was being used for a VLV and would report a “fake” slice in response to the disk query. In more preferred embodiments, when a raw or legacy device  170  is added to a VLV, a “fake” DSP-like partition is created on the MIC  112 . Then, any time a VLV is seen by a NMS, it creates a “slice” and adds it to the storage resource pool  140 . 
     FIGS. 2 and 3  illustrate the creation of a simple virtualized legacy volume (VLV).  FIG. 2  illustrates a volume tree  200  of a VLV and shows a VLV being created with a single legacy device  230 . A first storage processor (SP)  210 , such as one provided as a data services platform, is shown to contain a concatenated VLV  214  that is created from a legacy device  230  that is presented by a host or second SP  220  which initially presents the legacy device  230  to the SP  210  as a raw partition or raw device  226 . The mapping of the VLV  214  to the host SP  220  should typically not require any significant modification as the VLV  214  acts like any other single partition concatenated volume. 
     FIG. 3  illustrates at a high level a method  300  of creating a VLV, such as the VLV  214  of  FIG. 2  and such as by operation of the storage system  100  of  FIG. 1 . As shown, the actions of the method  300  are carried out by portions of a data services platform including a management interface or MIC  310 , a block virtualization manager or BV  312 , a virtualization configuration manager or VCM  314 , a master virtualization storage processor or MVSP  316 , and a volume state manager database or VSMDB  318  (typically in conjunction with operation of a volume state manager (VSM)  124  as shown in  FIG. 1 ). At step  321 , the MIC  310  locates available ALUs (e.g., all captive and legacy storage devices  150 ,  170 ). During  321 , the MIC  310  may execute a storage scan that locates all the available storage devices linked to its data services platform or DSP (such as DSP  110  of  FIG. 1 ). In this case, the legacy device(s) show up as an “unitialized” storage device or disk with no slices. 
   At  322 , the MIC  310  allows the legacy device to be used as the only element of the new VLV and sets the VLV flag in the volume structure to indicate the new volume is a VLV. Further at  322 , the MIC  310  issues a volume request to the BV  312 . At  323 , the BV requests volume element (e.g., ALU) information from the MIC  310  for the legacy device. Then, at  324 , the BV  312  uses the ALU information for the legacy device to request extent and disk information from the VCM  314 . The method  300  continues at  325  with the BV building the volume tree (see  FIG. 2 ) using the legacy device (such as legacy device  170  or  230 ), e.g., slice is set at −1, and forwards the tree to the VCM  325 . Again, the volume or volume tree is marked as a VLV. 
   At  326 , the VCM  314  notifies the MVSP  316  of a volume configuration change. The method  300  continues at  327  with the MVSP  316  receiving the request from the VCM  314 , and in response, the MVSP  316  requests from the VCM  314  a list of extents associated with the new volume (i.e., the new VLV). The MVSP  316  also requests from the VCM  314  volume information for the new VLV. At  328 , the MVSP  316  validates the received extent information and also, verifies that the VLV objects being created do not already exist. This may be accomplished via queries to the VSMDB  318 . 
   If these validations are successful, the MVSP  316  at  329  creates and writes the VLV database objects to the VSMDB  318 . For example, the MVSP  316  may check in-memory (e.g., “alu_arr”) to validate the legacy device. The MVSP may also request a raw or legacy device list from the VSMDB  318  and see VLV flags. As shown, the VSMDB  318  creates or manages a global set  350  of captive storage devices (or captive or DSP-owned ALUs) that have a reserved configuration metadata region (MDR)  340 ,  360  and within each of these MDRs  340 ,  360  a global set (GS)  342 ,  362  is stored including device configuration information, such as volume information and the like, for each device in the storage pool. This global set of information  342 ,  362  is useful for providing data services such as virtualization, and significantly, is shown to include VLV data  344 ,  364  that is created as part of the VLV generation process  300 . In other words, the global set of information  342 ,  362  stores configuration and state information persistently. At  330 , the MVSP  316  sends the volume tree and creation response to the VCM  314 . After successful completion of the VLV generation  300 , a “show volume” request or instruction may result in a volume name (such as vol/vlv and/or disk/4/3/2/0 or the like), a volume type (such as SAN or the like and/or concatenated), a volume size (such as a listing of the available storage space), a volume state (such as free, online, and the like), and a condition of the VLV (such as “intact” or the like). 
     FIGS. 4 and 5  illustrate the creation of a VLV with a legacy device with the snapshot data services feature.  FIG. 4  illustrates a volume tree  400  for a VLV with a dynamic COW pool, and  FIG. 5  illustrates a method  500  for creating such a VLV. In one embodiment, a legacy device  450  (such as a 17.09 GB legacy device or the like) is made accessible via a host storage processor  440 , and the VLV and dynamic COW pool created based on the legacy device  450  are the size of the legacy device  450 . The volume tree  400  is shown to include a storage process (SP) or DSP  410  with a concatenated volume or VLV  412  along with a point in time image (PIT) or snapshot volume or VLV  416 . These volumes are made available via a snapshot SRC  420  that includes a snap partition  422  mapped to a raw partition  424 , a snapshot COW  426 , and a snapshot log  428 . The snapshot COW  426  and snapshot log  428  are mapped to a dynamic COW ALU  430  with a MDR  434  but in some cases the COW  426  and log  428  may be separate ALUs. A communication link (e.g., an iSCSI link)  442  is provided to the logic/processor hardware  448  of the host SP  440  that is providing the legacy device  450  to the storage pool controlled by SP  410 . Note, the dynamic COW pool  430  is not provided on the legacy device  450 , which prevents alteration or damage of existing legacy or user data, and in some cases the legacy device  450  may also be connected to the snapshot SRC  420 . 
     FIG. 5  illustrate creation  500  of a VLV with snapshot. The components of a DSP responsible for performing the creation method  500  are shown and include a MIC  510 , a BV  512 , a VCM  514 , a MVSP  516 , and a VSMDB  518 . At step  521 , the MIC executes a storage scan that locates all the available storage devices linked to the DSP (such as devices  150 ,  170  linked via link  130  to DSP  110  as shown in  FIG. 1 ). For example, a legacy device (such as device  170  or  450 ) shows up in the storage scan as an “uninitialized” disk or device with no slices. At  522 , the MIC allows the located legacy device to be used as the first element of the VLV and sets the VLV flag in the volume structure. Since this volume is a VLV, the MIC verifies that there is space for the desired dynamic COW pool on a different ALU, i.e., on a captive or DSP owned storage device. Also, at  522 , the MIC issues a volume request to the BV  512 . 
   The method  500  continues at  523  with the BV  512  requesting or getting element information regarding the legacy device and additional/different ALU for the volume from the MIC  510 . The BV  512  checks applicable snapshot rules and validates that the elements conform to snapshot rules for VLV. At  524 , the BV  512  requests extent and disk information for the applicable ALUs from the VCM  514 , and then, at  525 , the BV  512  validates the legacy device and additional/different storage device or captive ALU. The BV  512  then builds the volume tree (see tree  400  of  FIG. 4 ) using the legacy device (see device  450  or device  170 ) and the ALU selected to be the dynamic COW ALU. The BV  512  then forwards the volume tree, which is marked as VLV tree, to the VCM  514 . 
   The VCM  514  responds by forwarding the request to the MVSP  516  at  526 . The method  500  continues at  527  with the MVSP  516  getting extent and volume information from the VCM  514 . At  528 , the MVSP  516  verifies the extent and partition information such as with comparison with volume object data (VOD)  540  in the MDR  540  of the dynamic COW or snapshot ALU. At  529 , the MVSP  516  interacts with the VSMDB  518  to update the VOD  542  on the snapshot ALU (see ALU  430  of  FIG. 4  or one of the resources  150  in  FIG. 1 ) with the COW and log partitions. The MVSP  516  also creates and writes VLV objects to the VLV database, e.g., VSMDB  518  or a portion of VSMDB  518 . Again, a global set of ALUs (or captive resources such as resources  150  in the storage pool)  560  are updated such that their reserved metadata regions  550 ,  570  include a global set of data  552 ,  572  that shows the updated VLV region  558 ,  578  showing the creation of the VLV for the particular legacy device (such as device  450  or  170 ). As part of  529 , the MVSP  516  requests raw or legacy device information from the VCM  514  and then, builds the volume tree, with a VLV tag. At  530 , the MVSP  516  returns the volume tree and creation status to the VCM  514 . 
     FIG. 6  illustrates how a DSP, such as DSP  110  of  FIG. 1 , may operate to delete a VLV and particularly, a VLV with an associated dynamic COW pool from a storage resource pool. The VLV deletion method  600  is shown again to be performed by a MIC  610 , a BV  612 , a VCM  614 , a MVSP  616 , and a VSMDB  618  of a DSP (not shown in  FIG. 6  but see platform  110  of  FIG. 1 ). At  621 , the MIC  610  sends a volume delete request to the BV  612 . The BV  612  at step  622  at to get extent information from the VCM  614 . The BV  612  then updates extent information and passes the updated volume information (e.g., updated volume tree) and updated extents to the VCM  614  along with the delete request. At  623 , the VCM  614  forwards the delete request to the MVSP  616 . 
   At  624 , with interaction with the VSMDB  618 , the MVSP  616  locates associated ALU information and updates the VOD  646  (or dynamic COW pool VOD) in the MDR  642  of the snapshot ALU  640 . At  625 . Again, the storage pool includes a global set of ALUs that each have a set aside configuration metadata region (MDR)  650 ,  660  with a global set of data used for data services  652 ,  662  including a VLV region  654 ,  664 , as the information for use in providing data services by the DSP is not placed on the legacy device corresponding to the VLV. At step  625 , the MVSP  616  removes VLV object(s) affected by the VLV delete request from the VLV region  654 ,  664  of the global set  652 ,  662  of the MDRs  650 ,  660  in the global set of ALUs  670 . At  626 , the MVSP  616  returns the volume deleted status to the VCM  614 . 
     FIG. 7  illustrates a VLV restoration process  700  performed by a data services platform (DSP), such as DSP  110  of  FIG. 1 , when the DSP is booted and a VLV was previously created in the storage system or storage resource pool. Again, the DSP includes an MIC  710 , a BV  712 , a VCM  714 , a VSM and MVSP  716 , and VSMDB  718  to perform various functions during the VLV restoration  700 . At step  721 , when the DSP is booted, the VCM  714  is initialized (e.g., at run level  3  on the NINE). At  722 , the VCM  714  selects a MVSP  716 , and sets up connections (e.g., iSCSI connections) to any DSP-owned or captive resources or ALUs that the MVSP  716  cannot see in the resource pool. At  723 , the VCM  714  builds a list of all the captive ALUs in the storage pool (e.g., on the chassis or the like) and sends the ALU list to the VSM/MVSP  716  along with a request to build volume trees. 
   The method  700  continues at  724  with the MVSP  716  receiving the device list and then, walking the list to build an in-memory ALU list or database  730 . At  725 , the MVSP  716  builds the volume trees  750  from this list which is stored in a device in the metadata region  740  as VOD  742 , and then, updates the in-memory tree database  750  via VSMDB  718 . At  725 , the MVSP  716  checks the VLV database for VLV information by inspecting the VLV region  754 ,  764  of the global set or region of data  752 ,  762  in the MDRs  750 ,  750  of the global set of captive or DSP-owned storage resources  770 . The MVSP  716  sees that one or more VLV exist in the storage pool and, in response, the MVSP  716  requests a list of raw devices from the VCM  714 . Using the VLV regions  754 ,  764  of the MDRs  750 ,  760  and applicable ALUs, the MVSP  716  builds the VLV volume tree(s). At  726 , the MVSP notifies the VCM  714  that the image is built and that there are extent and volume changes. At  727 , the VCM  714  queries the MVSP  716  for extent and volume information builds it own copy of the volume trees. 
   In preferred embodiments of the invention, VLVs are configured to support multi-path features as the case with other volumes formed for a DSP-owned or captive storage resource or device. These multi-path features include symmetric access from multiple host ports among other features.  FIG. 8  illustrates a multi-path volume tree for a single device VLV (e.g., a VLV formed based on legacy device  860 ) that is mapped to a host  810  with multi-path support. The VCM in the DSP configures the proper connections, e.g., multi-path iSCSI link  848 . As shown, the two paths are provided to the legacy device  860  to storage processors  840 ,  850  with link  848  connecting logic/hardware  854  of storage processor  850  with MP  846  of storage processor  840 . Symmetry is provided in the system  800  as host  810  can access the virtualized legacy volume provided by legacy device  860  via concatenated VLVs  824 ,  836  provided by storage processors  820 ,  830 , which each are mapped to the raw partition  842  maintained by storage processor  840 . 
   Although the invention has been described and illustrated with a certain degree of particularity, it is understood that the present disclosure has been made only by way of example, and that numerous changes in the combination and arrangement of parts can be resorted to by those skilled in the art without departing from the spirit and scope of the invention, as hereinafter claimed.