Patent Publication Number: US-2021176513-A1

Title: Storage virtual machine relocation

Description:
RELATED APPLICATIONS 
     This application claims priority to and is a continuation of U.S. application Ser. No. 16/456,846 filed on Jun. 28, 2019, now allowed, titled “STORAGE VIRTUAL MACHINE RELOCATION,” which claims priority to and is a continuation of U.S. Pat. No. 10,346,194 filed on Feb. 22, 2018 and titled “STORAGE VIRTUAL MACHINE RELOCATION,” which claims priority to and is a continuation of U.S. Pat. No. 9,940,154 filed on Oct. 15, 2015 and titled “STORAGE VIRTUAL MACHINE RELOCATION,” which are incorporated herein by reference. 
    
    
     BACKGROUND 
     A storage network environment may comprise one or more storage clusters of storage controllers (e.g., nodes) configured to provide clients with access to user data stored within storage devices. For example, a first storage cluster may comprise a first storage controller hosting a first storage virtual machine (e.g., a virtual server) configured to provide clients with access to user data stored, through a storage aggregate, across one or more storage devices owned by the first storage cluster. A second storage cluster may be configured according to a disaster recovery relationship with respect to the first storage cluster, such that user data (e.g., client I/O operations may be split into two I/O operations that write user data to a local storage device at the first storage cluster and mirror the user data to a remote storage device at the second storage cluster so that two copies of user data are maintained across storage clusters), configuration data (e.g., volume information, a replication policy, a network interface configuration, etc.), and write caching data (e.g., data cached within a non-volatile random-access memory (NVRAM) of the first storage controller before being written/flushed to a storage device during a consistency point) are replicated from the first storage cluster to the second storage cluster and vice versa. In this way, when a disaster occurs at the first storage cluster and clients are unable to access user data within the first storage device because the first storage controller may be unavailable or may have failed from the disaster, a second storage controller of the second storage cluster may provide clients with failover client access (e.g., a temporary switchover of ownership of storage devices and storage virtual machines) to replicated user data that was replicated from the first storage device to a mirrored storage device accessible to the second storage controller. When the first storage cluster recovers from the disaster, the second storage cluster may switch back (e.g., a switch back of ownership of the storage devices and storage virtual machines) to the first storage cluster, such that the first storage controller provides clients with access to user data from the first storage device (e.g., the first storage device may be synchronized with any changes made to user data and/or configuration data within the mirrored storage device during switchover operation by the second storage controller). In this way, user data, cached data, and configuration data may be backed up between storage clusters for disaster recovery. 
     A storage cluster may locally host multiple local storage virtual machines that are actively providing clients with access to user data of the storage cluster. The storage virtual machines are replicated to a remote storage cluster, such that replicated storage virtual machines at the remote storage cluster are dormant until a switchover occurs from the storage cluster to the remote storage cluster due to a failure of the storage cluster. The remote storage cluster may locally host virtual storage machines that are actively providing clients with access to user data of the remote storage cluster. Such storage virtual machines are replicated to the storage cluster, such that replicated storage virtual machines at the storage cluster are dormant until a switchover occurs from the remote storage cluster to the storage cluster due to a failure of the remote storage cluster. Unfortunately, load balancing technology may not exist for balancing workload between storage clusters of a storage network environment. Thus, if the storage cluster experiences a relatively higher load than the remote storage cluster, clients of the storage cluster may experience increased latency and/or other performance issues. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a component block diagram illustrating an example clustered network in accordance with one or more of the provisions set forth herein. 
         FIG. 2  is a component block diagram illustrating an example data storage system in accordance with one or more of the provisions set forth herein. 
         FIG. 3  is a flow chart illustrating an exemplary method of storage virtual machine relocation between storage clusters. 
         FIG. 4A  is a component block diagram illustrating an exemplary system for storage virtual machine relocation between storage clusters, where a storage virtual machine (A 2 ) of a storage cluster (A) is providing clients with access to user data of a storage aggregate (A 2 ). 
         FIG. 4B  is a component block diagram illustrating an exemplary system for storage virtual machine relocation between storage clusters, where ownership of a second set of storage devices of a storage aggregate (A 2 ) is switched from a storage cluster (A) to a storage cluster (B). 
         FIG. 4C  is a component block diagram illustrating an exemplary system for storage virtual machine relocation between storage clusters, where ownership of a storage aggregate (A 2 ) is switched from a storage cluster (A) to a storage cluster (B). 
         FIG. 4D  is a component block diagram illustrating an exemplary system for storage virtual machine relocation between storage clusters, where ownership of a storage virtual machine (A 2 ) and a replicated storage virtual machine (A 2 -DR) are switched from a storage cluster (A) to a storage cluster (B) for load balancing. 
         FIG. 5A  is a component block diagram illustrating an exemplary system for temporary storage virtual machine relocation between storage clusters at a storage virtual machine granularity in response to a disaster of a storage cluster, where a storage virtual machine (A 2 ) of a storage cluster (A) is providing clients with access to user data of a storage aggregate (A 2 ). 
         FIG. 5B  is a component block diagram illustrating an exemplary system for temporary storage virtual machine relocation between storage clusters at a storage virtual machine granularity in response to a disaster of a storage cluster, where a storage cluster (A) experiences a disaster. 
         FIG. 5C  is a component block diagram illustrating an exemplary system for temporary storage virtual machine relocation between storage clusters at a storage virtual machine granularity in response to a disaster of a storage cluster, where ownership of a second set of storage devices of a storage aggregate (A 2 ) is switched from a storage cluster (A) to a storage cluster (B). 
         FIG. 5D  is a component block diagram illustrating an exemplary system for temporary storage virtual machine relocation between storage clusters at a storage virtual machine granularity in response to a disaster of a storage cluster, where ownership of a storage aggregate (A 2 ) is switched from a storage cluster (A) to a storage cluster (B). 
         FIG. 5E  is a component block diagram illustrating an exemplary system for temporary storage virtual machine relocation between storage clusters at a storage virtual machine granularity in response to a disaster of a storage cluster, where a replicated storage virtual machine (A 2 -DR) is switched from a dormant state to an active state. 
         FIG. 5F  is a component block diagram illustrating an exemplary system for temporary storage virtual machine relocation between storage clusters at a storage virtual machine granularity in response to a disaster of a storage cluster, where a switchback operation is performed based upon a storage cluster (A) recovering from a disaster. 
         FIG. 6  is an example of a computer readable medium in accordance with one or more of the provisions set forth herein. 
     
    
    
     DETAILED DESCRIPTION 
     Some examples of the claimed subject matter are now described with reference to the drawings, where like reference numerals are generally used to refer to like elements throughout. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide an understanding of the claimed subject matter. It may be evident, however, that the claimed subject matter may be practiced without these specific details. Nothing in this detailed description is admitted as prior art. 
     One or more techniques and/or devices for storage virtual machine relocation (e.g., a change in ownership) between storage clusters are provided. Operational statistics (e.g., a number of client I/O requests, a current latency of processing client I/O requests, a latency of performing backup and replication functionality, an amount of over-utilized or underutilized resources, etc.) of a first storage cluster and a second storage cluster are evaluated to identify a set of load balancing metrics. For example, the set of load balancing metrics may indicate that the first storage cluster has a first operational load that is a threshold amount greater than the second storage cluster (e.g., the second storage cluster may have more available resources for processing client I/O request, whereas the first storage cluster may be overburdened with work). Accordingly, ownership of a first storage aggregate may be switched from the first storage cluster to the second storage cluster. Ownership of a storage virtual machine and a replicated storage virtual machine, configured to provide access to user data through the first storage aggregate, may be switched from the first storage cluster to the second storage cluster. The replicated storage virtual machine may be switched into an active state for facilitating client access, from the second storage cluster, to user data stored through the first storage aggregate. 
     In this way, ownership of storage aggregates and/or storage virtual machines may be changed (e.g., permanently changed for load balancing purposes or temporarily changed at a storage virtual machine granularity for disaster recovery purposes) between the first storage cluster and the second storage cluster, at a storage virtual machine granularity (e.g., merely a selected set of storage virtual machines may be relocated, such as having a change in ownership, based upon the load balancing metrics), utilizing zero-copy ownership change operations (e.g., ownership of the storage aggregate may be changed without copying data from the first storage cluster to the second storage cluster because client I/O operations for the first storage aggregate are already mirrored between a local storage device of the first storage cluster and a remote mirror storage device of the second storage cluster during processing of the client I/O operations) without disrupting client access to user data. 
     To provide context for storage virtual machine relocation (e.g., a change in ownership) between storage clusters,  FIG. 1  illustrates an embodiment of a clustered network environment  100  or a network storage environment. It may be appreciated, however, that the techniques, etc. described herein may be implemented within the clustered network environment  100 , a non-cluster network environment, and/or a variety of other computing environments, such as a desktop computing environment. That is, the instant disclosure, including the scope of the appended claims, is not meant to be limited to the examples provided herein. It will be appreciated that where the same or similar components, elements, features, items, modules, etc. are illustrated in later figures but were previously discussed with regard to prior figures, that a similar (e.g., redundant) discussion of the same may be omitted when describing the subsequent figures (e.g., for purposes of simplicity and ease of understanding). 
       FIG. 1  is a block diagram illustrating an example clustered network environment  100  that may implement at least some embodiments of the techniques and/or systems described herein. The example environment  100  comprises data storage systems or storage sites  102  and  104  that are coupled over a cluster fabric  106 , such as a computing network embodied as a private Infiniband, Fibre Channel (FC), or Ethernet network facilitating communication between the storage systems  102  and  104  (and one or more modules, component, etc. therein, such as, nodes  116  and  118 , for example). It will be appreciated that while two data storage systems  102  and  104  and two nodes  116  and  118  are illustrated in  FIG. 1 , that any suitable number of such components is contemplated. In an example, nodes  116 ,  118  comprise storage controllers (e.g., node  116  may comprise a primary or local storage controller and node  118  may comprise a secondary or remote storage controller) that provide client devices, such as host devices  108 ,  110 , with access to data stored within data storage devices  128 ,  130 . Similarly, unless specifically provided otherwise herein, the same is true for other modules, elements, features, items, etc. referenced herein and/or illustrated in the accompanying drawings. That is, a particular number of components, modules, elements, features, items, etc. disclosed herein is not meant to be interpreted in a limiting manner. 
     It will be further appreciated that clustered networks are not limited to any particular geographic areas and can be clustered locally and/or remotely. Thus, in one embodiment a clustered network can be distributed over a plurality of storage systems and/or nodes located in a plurality of geographic locations; while in another embodiment a clustered network can include data storage systems (e.g.,  102 ,  104 ) residing in a same geographic location (e.g., in a single onsite rack of data storage devices). 
     In the illustrated example, one or more host devices  108 ,  110  which may comprise, for example, client devices, personal computers (PCs), computing devices used for storage (e.g., storage servers), and other computers or peripheral devices (e.g., printers), are coupled to the respective data storage systems  102 ,  104  by storage network connections  112 ,  114 . Network connection may comprise a local area network (LAN) or wide area network (WAN), for example, that utilizes Network Attached Storage (NAS) protocols, such as a Common Internet File System (CIFS) protocol or a Network File System (NFS) protocol to exchange data packets. Illustratively, the host devices  108 ,  110  may be general-purpose computers running applications, and may interact with the data storage systems  102 ,  104  using a client/server model for exchange of information. That is, the host device may request data from the data storage system (e.g., data on a storage device managed by a network storage control configured to process I/O commands issued by the host device for the storage device), and the data storage system may return results of the request to the host device via one or more network connections  112 ,  114 . 
     The nodes  116 ,  118  on clustered data storage systems  102 ,  104  can comprise network or host nodes that are interconnected as a cluster to provide data storage and management services, such as to an enterprise having remote locations, cloud storage (e.g., a storage endpoint may be stored within a data cloud), etc., for example. Such a node in a data storage and management network cluster environment  100  can be a device attached to the network as a connection point, redistribution point or communication endpoint, for example. A node may be capable of sending, receiving, and/or forwarding information over a network communications channel, and could comprise any device that meets any or all of these criteria. One example of a node may be a data storage and management server attached to a network, where the server can comprise a general purpose computer or a computing device particularly configured to operate as a server in a data storage and management system. 
     In an example, a first cluster of nodes such as the nodes  116 ,  118  (e.g., a first set of storage controllers configured to provide access to a first storage aggregate comprising a first logical grouping of one or more storage devices) may be located on a first storage site. A second cluster of nodes, not illustrated, may be located at a second storage site (e.g., a second set of storage controllers configured to provide access to a second storage aggregate comprising a second logical grouping of one or more storage devices). The first cluster of nodes and the second cluster of nodes may be configured according to a disaster recovery configuration where a surviving cluster of nodes provides switchover access to storage devices of a disaster cluster of nodes in the event a disaster occurs at a disaster storage site comprising the disaster cluster of nodes (e.g., the first cluster of nodes provides client devices with switchover data access to storage devices of the second storage aggregate in the event a disaster occurs at the second storage site). 
     As illustrated in the exemplary environment  100 , nodes  116 ,  118  can comprise various functional components that coordinate to provide distributed storage architecture for the cluster. For example, the nodes can comprise a network module  120 ,  122  and a data module  124 ,  126 . Network modules  120 ,  122  can be configured to allow the nodes  116 ,  118  (e.g., network storage controllers) to connect with host devices  108 ,  110  over the network connections  112 ,  114 , for example, allowing the host devices  108 ,  110  to access data stored in the distributed storage system. Further, the network modules  120 ,  122  can provide connections with one or more other components through the cluster fabric  106 . For example, in  FIG. 1 , a first network module  120  of first node  116  can access a second data storage device  130  by sending a request through a second data module  126  of a second node  118 . 
     Data modules  124 ,  126  can be configured to connect one or more data storage devices  128 ,  130 , such as disks or arrays of disks, flash memory, or some other form of data storage, to the nodes  116 ,  118 . The nodes  116 ,  118  can be interconnected by the cluster fabric  106 , for example, allowing respective nodes in the cluster to access data on data storage devices  128 ,  130  connected to different nodes in the cluster. Often, data modules  124 ,  126  communicate with the data storage devices  128 ,  130  according to a storage area network (SAN) protocol, such as Small Computer System Interface (SCSI) or Fiber Channel Protocol (FCP), for example. Thus, as seen from an operating system on a node  116 ,  118 , the data storage devices  128 ,  130  can appear as locally attached to the operating system. In this manner, different nodes  116 ,  118 , etc. may access data blocks through the operating system, rather than expressly requesting abstract files. 
     It should be appreciated that, while the example embodiment  100  illustrates an equal number of network and data modules, other embodiments may comprise a differing number of these modules. For example, there may be a plurality of network and data modules interconnected in a cluster that does not have a one-to-one correspondence between the network and data modules. That is, different nodes can have a different number of network and data modules, and the same node can have a different number of network modules than data modules. 
     Further, a host device  108 ,  110  can be networked with the nodes  116 ,  118  in the cluster, over the networking connections  112 ,  114 . As an example, respective host devices  108 ,  110  that are networked to a cluster may request services (e.g., exchanging of information in the form of data packets) of a node  116 ,  118  in the cluster, and the node  116 ,  118  can return results of the requested services to the host devices  108 ,  110 . In one embodiment, the host devices  108 ,  110  can exchange information with the network modules  120 ,  122  residing in the nodes (e.g., network hosts)  116 ,  118  in the data storage systems  102 ,  104 . 
     In one embodiment, the data storage devices  128 ,  130  comprise volumes  132 , which is an implementation of storage of information onto disk drives or disk arrays or other storage (e.g., flash) as a file-system for data, for example. Volumes can span a portion of a disk, a collection of disks, or portions of disks, for example, and typically define an overall logical arrangement of file storage on disk space in the storage system. In one embodiment a volume can comprise stored data as one or more files that reside in a hierarchical directory structure within the volume. 
     Volumes are typically configured in formats that may be associated with particular storage systems, and respective volume formats typically comprise features that provide functionality to the volumes, such as providing an ability for volumes to form clusters. For example, where a first storage system may utilize a first format for their volumes, a second storage system may utilize a second format for their volumes. 
     In the example environment  100 , the host devices  108 ,  110  can utilize the data storage systems  102 ,  104  to store and retrieve data from the volumes  132 . In this embodiment, for example, the host device  108  can send data packets to the network module  120  in the node  116  within data storage system  102 . The node  116  can forward the data to the data storage device  128  using the data module  124 , where the data storage device  128  comprises volume  132 A. In this way, in this example, the host device can access the storage volume  132 A, to store and/or retrieve data, using the data storage system  102  connected by the network connection  112 . Further, in this embodiment, the host device  110  can exchange data with the network module  122  in the host  118  within the data storage system  104  (e.g., which may be remote from the data storage system  102 ). The host  118  can forward the data to the data storage device  130  using the data module  126 , thereby accessing volume  1328  associated with the data storage device  130 . 
     It may be appreciated that storage virtual machine relocation (e.g., a change in ownership) between storage clusters may be implemented within the clustered network environment  100 . For example, a relocation component may be implemented for the node  116  and/or the node  118 . The relocation component may be configured to relocate a storage virtual machine between the node  116  and the node  118 , where the node  116  is hosted within a first storage cluster and the node  118  is hosted within a second storage cluster. In this way, storage virtual machines may be permanently relocated, at a storage virtual machine granularity, between storage clusters utilizing zero-copy ownership change operations for load balancing without client interruption to user data. It may be appreciated that storage virtual machine relocation may be implemented for and/or between any type of computing environment, and may be transferrable between physical devices (e.g., node  116 , node  118 , etc.) and/or a cloud computing environment (e.g., remote to the clustered network environment  100 ). 
       FIG. 2  is an illustrative example of a data storage system  200  (e.g.,  102 ,  104  in  FIG. 1 ), providing further detail of an embodiment of components that may implement one or more of the techniques and/or systems described herein. The example data storage system  200  comprises a node  202  (e.g., host nodes  116 ,  118  in  FIG. 1 ), and a data storage device  234  (e.g., data storage devices  128 ,  130  in  FIG. 1 ). The node  202  may be a general purpose computer, for example, or some other computing device particularly configured to operate as a storage server. A host device  205  (e.g.,  108 ,  110  in  FIG. 1 ) can be connected to the node  202  over a network  216 , for example, to provides access to files and/or other data stored on the data storage device  234 . In an example, the node  202  comprises a storage controller that provides client devices, such as the host device  205 , with access to data stored within data storage device  234 . 
     The data storage device  234  can comprise mass storage devices, such as disks  224 ,  226 ,  228  of a disk array  218 ,  220 ,  222 . It will be appreciated that the techniques and systems, described herein, are not limited by the example embodiment. For example, disks  224 ,  226 ,  228  may comprise any type of mass storage devices, including but not limited to magnetic disk drives, flash memory, and any other similar media adapted to store information, including, for example, data (D) and/or parity (P) information. 
     The node  202  comprises one or more processors  204 , a memory  206 , a network adapter  210 , a cluster access adapter  212 , and a storage adapter  214  interconnected by a system bus  242 . The storage system  200  also includes an operating system  208  installed in the memory  206  of the node  202  that can, for example, implement a Redundant Array of Independent (or Inexpensive) Disks (RAID) optimization technique to optimize a reconstruction process of data of a failed disk in an array. 
     The operating system  208  can also manage communications for the data storage system, and communications between other data storage systems that may be in a clustered network, such as attached to a cluster fabric  215  (e.g.,  106  in  FIG. 1 ). Thus, the node  202 , such as a network storage controller, can respond to host device requests to manage data on the data storage device  234  (e.g., or additional clustered devices) in accordance with these host device requests. The operating system  208  can often establish one or more file systems on the data storage system  200 , where a file system can include software code and data structures that implement a persistent hierarchical namespace of files and directories, for example. As an example, when a new data storage device (not shown) is added to a clustered network system, the operating system  208  is informed where, in an existing directory tree, new files associated with the new data storage device are to be stored. This is often referred to as “mounting” a file system. 
     In the example data storage system  200 , memory  206  can include storage locations that are addressable by the processors  204  and adapters  210 ,  212 ,  214  for storing related software application code and data structures. The processors  204  and adapters  210 ,  212 ,  214  may, for example, include processing elements and/or logic circuitry configured to execute the software code and manipulate the data structures. The operating system  208 , portions of which are typically resident in the memory  206  and executed by the processing elements, functionally organizes the storage system by, among other things, invoking storage operations in support of a file service implemented by the storage system. It will be apparent to those skilled in the art that other processing and memory mechanisms, including various computer readable media, may be used for storing and/or executing application instructions pertaining to the techniques described herein. For example, the operating system can also utilize one or more control files (not shown) to aid in the provisioning of virtual machines. 
     The network adapter  210  includes the mechanical, electrical and signaling circuitry needed to connect the data storage system  200  to a host device  205  over a computer network  216 , which may comprise, among other things, a point-to-point connection or a shared medium, such as a local area network. The host device  205  (e.g.,  108 ,  110  of  FIG. 1 ) may be a general-purpose computer configured to execute applications. As described above, the host device  205  may interact with the data storage system  200  in accordance with a client/host model of information delivery. 
     The storage adapter  214  cooperates with the operating system  208  executing on the node  202  to access information requested by the host device  205  (e.g., access data on a storage device managed by a network storage controller). The information may be stored on any type of attached array of writeable media such as magnetic disk drives, flash memory, and/or any other similar media adapted to store information. In the example data storage system  200 , the information can be stored in data blocks on the disks  224 ,  226 ,  228 . The storage adapter  214  can include input/output (I/O) interface circuitry that couples to the disks over an I/O interconnect arrangement, such as a storage area network (SAN) protocol (e.g., Small Computer System Interface (SCSI), iSCSI, hyperSCSI, Fiber Channel Protocol (FCP)). The information is retrieved by the storage adapter  214  and, if necessary, processed by the one or more processors  204  (or the storage adapter  214  itself) prior to being forwarded over the system bus  242  to the network adapter  210  (and/or the cluster access adapter  212  if sending to another node in the cluster) where the information is formatted into a data packet and returned to the host device  205  over the network connection  216  (and/or returned to another node attached to the cluster over the cluster fabric  215 ). 
     In one embodiment, storage of information on arrays  218 ,  220 ,  222  can be implemented as one or more storage “volumes”  230 ,  232  that are comprised of a cluster of disks  224 ,  226 ,  228  defining an overall logical arrangement of disk space. The disks  224 ,  226 ,  228  that comprise one or more volumes are typically organized as one or more groups of RAIDs. As an example, volume  230  comprises an aggregate of disk arrays  218  and  220 , which comprise the cluster of disks  224  and  226 . 
     In one embodiment, to facilitate access to disks  224 ,  226 ,  228 , the operating system  208  may implement a file system (e.g., write anywhere file system) that logically organizes the information as a hierarchical structure of directories and files on the disks. In this embodiment, respective files may be implemented as a set of disk blocks configured to store information, whereas directories may be implemented as specially formatted files in which information about other files and directories are stored. 
     Whatever the underlying physical configuration within this data storage system  200 , data can be stored as files within physical and/or virtual volumes, which can be associated with respective volume identifiers, such as file system identifiers (FSIDs), which can be 32-bits in length in one example. 
     A physical volume corresponds to at least a portion of physical storage devices whose address, addressable space, location, etc. doesn&#39;t change, such as at least some of one or more data storage devices  234  (e.g., a Redundant Array of Independent (or Inexpensive) Disks (RAID system)). Typically the location of the physical volume doesn&#39;t change in that the (range of) address(es) used to access it generally remains constant. 
     A virtual volume, in contrast, is stored over an aggregate of disparate portions of different physical storage devices. The virtual volume may be a collection of different available portions of different physical storage device locations, such as some available space from each of the disks  224 ,  226 , and/or  228 . It will be appreciated that since a virtual volume is not “tied” to any one particular storage device, a virtual volume can be said to include a layer of abstraction or virtualization, which allows it to be resized and/or flexible in some regards. 
     Further, a virtual volume can include one or more logical unit numbers (LUNs)  238 , directories  236 , Qtrees  235 , and files  240 . Among other things, these features, but more particularly LUNS, allow the disparate memory locations within which data is stored to be identified, for example, and grouped as data storage unit. As such, the LUNs  238  may be characterized as constituting a virtual disk or drive upon which data within the virtual volume is stored within the aggregate. For example, LUNs are often referred to as virtual drives, such that they emulate a hard drive from a general purpose computer, while they actually comprise data blocks stored in various parts of a volume. 
     In one embodiment, one or more data storage devices  234  can have one or more physical ports, wherein each physical port can be assigned a target address (e.g., SCSI target address). To represent respective volumes stored on a data storage device, a target address on the data storage device can be used to identify one or more LUNs  238 . Thus, for example, when the node  202  connects to a volume  230 ,  232  through the storage adapter  214 , a connection between the node  202  and the one or more LUNs  238  underlying the volume is created. 
     In one embodiment, respective target addresses can identify multiple LUNs, such that a target address can represent multiple volumes. The I/O interface, which can be implemented as circuitry and/or software in the storage adapter  214  or as executable code residing in memory  206  and executed by the processors  204 , for example, can connect to volume  230  by using one or more addresses that identify the LUNs  238 . 
     It may be appreciated that storage virtual machine relocation (e.g., change in ownership) between storage clusters may be implemented for the data storage system  200 . For example, a relocation component may be implemented for the node  202  of a first storage cluster and a second node of a second storage cluster. The relocation component may be configured to relocate a storage virtual machine between the node  202  and the second node. In this way, storage virtual machines may be permanently relocated, at a storage virtual machine granularity, between storage clusters utilizing zero-copy ownership change operations for load balancing without client interruption to user data. It may be appreciated that storage virtual machine relocation may be implemented for and/or between any type of computing environment, and may be transferrable between physical devices (e.g., node  202 , host  205 , etc.) and/or a cloud computing environment (e.g., remote to the node  202  and/or the host  205 ). 
     One embodiment of storage virtual machine relocation (e.g., change in ownership) between storage clusters is illustrated by an exemplary method  300  of  FIG. 3 . At  302 , operational statistics of a first storage cluster and a second storage cluster are evaluated to determine that the first storage cluster has a first operational load and that the second storage cluster has a second operational load. An operational load may correspond to a load on a storage cluster in relation to resources of the storage cluster (e.g., a latency of processing client I/O operations, available hardware resources of storage controllers, bandwidth, etc.). The first storage cluster may comprise a first storage virtual machine associated with a first storage aggregate, a second storage virtual machine associated with a second storage aggregate, and/or other storage virtual machines associated with other storage aggregates. The storage virtual machines, hosted by the first storage cluster, may be replicated (configuration data replicated using a configuration replication layer, cached data of an NVRAM replicated using NVRAM mirroring, etc.) to the second storage cluster as replicated storage virtual machines located at the second storage cluster but initially owned by the first storage cluster. The storage virtual machines may be in an active state for facilitating client access to user data within the storage aggregates of the first storage cluster, and the replicated virtual machines may be in a dormant state waiting to provide failover client access to user data in the event the first storage cluster fails or has a disaster. 
     A storage aggregate may be stored across one or more storage devices according to a data mirroring configuration. A RAID synchronous mirroring solution may be implemented where a client I/O operation to the storage aggregate is split into two operations where data is stored within a local storage device of a local storage cluster by a first operation and a backup mirror of the data is stored within a remote mirror storage device of a remote storage cluster. For example, a write operation to the first storage aggregate may be split into a first operation that stores data of the write operation within a first storage device of the first storage cluster (e.g., during a flush of an NVRAM, within which the data of the write operation may have been cached, of the first storage controller into a local storage device) and within a mirror storage device of the second storage cluster. In this way, data within the first storage aggregate may be stored within the first storage cluster and mirrored to the second storage cluster. 
     The first operational load may be compared to the second operational load to determine whether the first storage cluster and/or the second storage cluster are overburdened with workloads or have available resources. For example, the first operational load may be determined as being a threshold amount greater than the second operational load, and thus load balancing of workloads from the first storage cluster to the second storage cluster may be beneficial. Accordingly, ownership of the first storage aggregate may be switched from the first storage cluster to the second storage cluster, at  304 . For example, the first storage aggregate may be unmounted. Ownership of a first storage device, associated with the first storage aggregate and maintained at the first storage cluster, may be changed from the first storage cluster to the second storage cluster. In an example, ownership of a mirror storage device, associated with the first storage aggregate as a mirror of the first storage aggregate and maintained at the second storage cluster, may be changed from the first storage cluster to the second storage cluster. The first storage aggregate may be onlined for ownership by the second storage cluster. A zero-copy ownership change operation may be performed to switch the ownership of the first storage aggregate because the mirror storage device, hosted at the second storage cluster, is a backup mirror already comprising replicated data of the first storage device, and thus little to no additional copying of user data to the second storage cluster may be performed, for example. In an example, the second storage cluster may be specified as a non-temporary owner (e.g., a permanent owner) of the first storage aggregate. 
     At  306 , ownership of the first storage virtual machine and the replicated storage virtual machine may be switched from the first storage cluster to the second storage cluster. At  308 , the replicated storage virtual machine may be switched to an active state for facilitating client access, from the second storage cluster, to user data stored through the first storage aggregate (e.g., replicated data stored within the mirror storage device). The first storage virtual machine may be switch to a dormant state. In an example, the second storage cluster may be designated as a non-temporary owner (e.g., a permanent owner) of the first storage virtual machine. Non-disruptive client access to data may be maintained through the first storage aggregate during switchover of ownership of the first storage aggregate, the first storage virtual machine, and/or the replicated storage virtual machine from the first storage cluster to the second storage cluster. In this way, ownership of one or more storage aggregates and one or more storage virtual machines may be permanently changed between the first storage cluster and the second storage cluster utilizing zero-copy ownership change operations based upon load balancing metrics associated with the first storage cluster and the second storage cluster without disrupting client access to user data. 
     In an example, storage virtual machines may be temporarily relocated between storage clusters at a storage virtual machine granularity such as for disaster recovery purposes. For example, the first storage cluster and the second storage cluster may be configured according to a disaster recovery relationship, such that the second storage cluster is configured to provide failover client access to data, replicated from the first storage cluster (e.g., access to data within a mirror storage device, of the second storage cluster, comprising replicated data mirrored from a storage device of the first storage cluster), responsive to a disaster occurring at the first storage cluster. The first storage cluster may comprise a third storage aggregate and a third storage virtual machine. The second storage cluster may comprise a replicated third storage virtual machine that is a replication of the third storage virtual machine. 
     Responsive to determining that the first storage cluster has experienced the disaster, a temporary switchover of ownership of the third storage aggregate, but not the second storage aggregate, may be performed from the first storage cluster to the second storage cluster based upon the disaster recovery relationship. For example, the first storage cluster may retain ownership of the third storage virtual machine and the replicated storage virtual machine, however, the replicated storage virtual machine may be switched from a dormant state to an active state for providing failover client access to the third storage aggregate temporarily owned by the second storage cluster. In this way, select storage aggregates may be temporarily relocated, at a storage virtual server granularity, for disaster recovery operation. 
     Responsive to determining that the first storage cluster has recovered to an operational state from the disaster, a switchback of ownership of the third storage aggregate may be performed from the second storage cluster to the first storage cluster. The third replicated storage virtual machine may be switched from the active state to the dormant state. The storage virtual machine may be set to the active state for providing primary client access to data from the third storage aggregate. 
       FIGS. 4A-4D  illustrate examples of a system  400 , comprising a relocation component  401 , for storage virtual machine relocation (e.g., change in ownership) between storage clusters. The relocation component  401  may be hosted within storage cluster (A)  402 , storage cluster (B)  404 , or a remote location having network connectivity to the storage cluster (A)  402  and/or the storage cluster (B)  404 . The storage cluster (A)  402  may comprise a storage controller (A 1 )  406 , a storage controller (A 2 )  416 , and/or other storage controllers not illustrated. The storage cluster (B)  404  may comprise a storage controller (B 1 )  418 , a storage controller (B 2 )  426 , and/or other storage controllers not illustrated. It may be appreciated that storage controllers and storage devices that are owned by the storage cluster (A)  402  are represented by a dotted fill, while storage controllers and storage devices that are owned by the storage cluster (B)  404  are represented by a slanted line fill. 
     A storage controller may be configured to provide clients with storage using storage aggregates hosted by storage virtual machines. In an example, the storage controller (A 1 )  406  may provide clients with storage through a storage aggregate (A 1 ) maintained by a storage virtual machine (A 1 )  408 . The storage aggregate (A 1 ) may comprise a first set of storage devices  430  (e.g., one or more storage devices hosted within the storage cluster (A)  402  and one or more mirrored storage devices hosted within the storage cluster (B)  404 , such that a client I/O operation to the storage aggregate (A 1 ) is written to both a storage device hosted within the storage cluster (A)  402  and a corresponding mirrored storage device hosted within the storage cluster (B)  404  for data redundancy and data loss mitigation). In another example, the storage controller (A 2 )  426  may provide clients with storage through a storage aggregate (A 2 ) maintained by a storage virtual machine (A 2 )  414 . The storage aggregate (A 2 ) may comprise a second set of storage devices  434  (e.g., one or more storage devices hosted within the storage cluster (A)  402  and one or more mirrored storage devices hosted within the storage cluster (B)  404 , such that a client I/O operation to the storage aggregate (A 2 ) is written to both a storage device hosted within the storage cluster (A)  402  and a corresponding mirrored storage device hosted within the storage cluster (B)  404  for data redundancy and data loss mitigation). 
     In another example, the storage controller (B 1 )  418  may provide clients with storage through a storage aggregate (B 1 ) maintained by a storage virtual machine (B 1 )  422 . The storage aggregate (B 1 ) may comprise a third set of storage devices  432  (e.g., one or more storage devices hosted within the storage cluster (B)  404  and one or more mirrored storage devices hosted within the storage cluster (A)  402 , such that a client I/O operation to the storage aggregate (B 1 ) is written to both a storage device hosted within the storage cluster (B)  404  and a corresponding mirrored storage device hosted within the storage cluster (A)  402  for data redundancy and data loss mitigation). 
     Replicated storage virtual machines, corresponding to replications of storage virtual machines at a different storage cluster, may be maintained at remote storage clusters in order to provide failover access to replicated user data in the event a disaster occurs at a storage cluster. For example, the storage cluster (B)  404  may host a replicated storage virtual machine (A 1 -DR)  420 , corresponding to a replication of the storage virtual machine (A 1 )  408 , and a replicated storage virtual machine (A 2 -DR)  424  corresponding to a replication of the storage virtual machine (A 2 )  414 , which may provide failover access to replicated user data in the event the storage cluster (A)  402  experiences a disaster. The storage cluster (A)  402  may host a replicated storage virtual machine (B 1 -DR)  410  corresponding to a replication of the storage virtual machine (B 1 )  422 , which may provide failover access to replicated user data in the event the storage cluster (B)  404  experiences a disaster. Within a pairing of storage virtual machines, merely a single storage virtual machine is active for providing access to user data while the other storage virtual machine is dormant (e.g., the replicated storage virtual machine (A 1 -DR)  420  is dormant while the storage virtual machine (A 1 )  408  is actively providing clients with access to user data). 
       FIG. 4A  illustrates the storage virtual machine (A 2 )  414  actively serving clients with access to user data of the storage aggregate (A 2 ) stored within the second set of storage devices  434  (e.g., from within storage devices hosted at the storage cluster (A)  402 , and where data is replicated to mirrored storage devices hosted at the storage cluster (B)  404 ) while the storage cluster (A)  402  has ownership  440  of the second set of storage devices  434  and the storage aggregate (A 2 ). The relocation component  401  may evaluate operational statistics of the storage cluster (A)  402  and the storage cluster (B)  404  to determine that an operational load of the storage cluster (A)  402  exceeds an operational load to the storage cluster (B)  404  by a threshold amount (e.g., latency, available resources, bandwidth, a number of clients being served, a number and frequency of client I/O operations, and/or other information may indicate that the storage cluster (B)  404  has more available resources and/or a lighter load than the storage cluster (A)  402 ). Accordingly, the relocation component  401  may perform a relocation (e.g., a change in ownership) of the storage virtual machine (A 2 )  414  from the storage cluster (A)  402  to the storage cluster (B)  404  for load balancing. 
       FIG. 4B  illustrates the relocation component  401  performing the relocation by initiating a switch of ownership  440 B of the second set of storage devices  434  of the storage aggregate (A 2 ) from the storage cluster (A)  402  to the storage cluster (B)  404 .  FIG. 4C  illustrates the relocation component  401  switching ownership of the storage aggregate (A 2 ) from the storage cluster (A)  402  to the storage cluster (B)  404 , which is illustrated by the second set of storage devices  434  having the slanted line fill, as opposed to the dotted fill, to illustrate ownership by the storage cluster (B)  404 . 
       FIG. 4D  illustrates the relocation component  401  switching ownership of the storage virtual machine (A 2 )  414  and the replicated storage virtual machine (A 2 -DR)  424  from the storage cluster (A)  402  to the storage cluster (B)  404 . The relocation component  401  may switch the storage virtual machine  414  into a dormant state and the replicated storage virtual machine (A 2 -DR)  424  into an active state for facilitating client access, from the storage cluster (B)  404 , to user data stored within the storage aggregate (A 2 ) such as data within the second set of storage devices  434  now owned by the storage cluster (B)  404 . In this way, load balancing may be achieved between the storage cluster (A)  402  and the storage cluster (B)  404  at a storage virtual machine granularity (e.g., resources of the storage controller (B 2 )  426  may now be used to host the replicated storage virtual machine (A 2 -DR)  424  in the active state). 
       FIGS. 5A-5F  illustrate examples of a system  500 , comprising a relocation component  501 , for temporary storage virtual machine relocation between storage clusters at a storage virtual machine granularity in response to a disaster of a storage cluster. The relocation component  501  may be hosted within storage cluster (A)  502 , storage cluster (B)  504 , or a remote location having network connectivity to the storage cluster (A)  502  and/or the storage cluster (B)  504 . The storage cluster (A)  502  may comprise a storage controller (A 1 )  506 , a storage controller (A 2 )  516 , and/or other storage controllers not illustrated. The storage cluster (B)  504  may comprise a storage controller (B 1 )  518 , a storage controller (B 2 )  526 , and/or other storage controllers not illustrated. It may be appreciated that storage controllers and storage devices that are owned by the storage cluster (A)  502  are represented by a dotted fill, while storage controllers and storage devices that are owned by the storage cluster (B)  504  are represented by a slanted line fill. 
     A storage controller may be configured to provide clients with storage using storage aggregates hosted by storage virtual machines. In an example, the storage controller (A 1 )  506  may provide clients with storage through a storage aggregate (A 1 ) maintained by a storage virtual machine (A 1 )  508 . The storage aggregate (A 1 ) may comprise a first set of storage devices  530  (e.g., one or more storage devices hosted within the storage cluster (A)  502  and one or more mirrored storage devices hosted within the storage cluster (B)  504 , such that a client I/O operation to the storage aggregate (A 1 ) is written to both a storage device hosted within the storage cluster (A)  502  and a corresponding mirrored storage device hosted within the storage cluster (B)  504  for data redundancy and data loss mitigation). In another example, the storage controller (A 2 )  526  may provide clients with storage through a storage aggregate (A 2 ) maintained by a storage virtual machine (A 2 )  514 . The storage aggregate (A 2 ) may comprise a second set of storage devices  534  (e.g., one or more storage devices hosted within the storage cluster (A)  502  and one or more mirrored storage devices hosted within the storage cluster (B)  504 , such that a client I/O operation to the storage aggregate (A 2 ) is written to both a storage device hosted within the storage cluster (A)  502  and a corresponding mirrored storage device hosted within the storage cluster (B)  504  for data redundancy and data loss mitigation). 
     In another example, the storage controller (B 1 )  518  may provide clients with storage through a storage aggregate (B 1 ) maintained by a storage virtual machine (B 1 )  522 . The storage aggregate (B 1 ) may comprise a third set of storage devices  532  (e.g., one or more storage devices hosted within the storage cluster (B)  504  and one or more mirrored storage devices hosted within the storage cluster (A)  502 , such that a client I/O operation to the storage aggregate (B 1 ) is written to both a storage device hosted within the storage cluster (B)  504  and a corresponding mirrored storage device hosted within the storage cluster (A)  502  for data redundancy and data loss mitigation). 
     Replicated storage virtual machines, corresponding to replications of storage virtual machines at a different storage cluster, may be maintained at remote storage clusters in order to provide failover access to replicated user data in the event a disaster occurs at a storage cluster. For example, the storage cluster (B)  504  may host a replicated storage virtual machine (A 1 -DR)  520 , corresponding to a replication of the storage virtual machine (A 1 )  508 , and a replicated storage virtual machine (A 2 -DR)  524  corresponding to a replication of the storage virtual machine (A 2 )  514 , which may provide failover access to replicated user data in the event the storage cluster (A)  502  experiences a disaster. The storage cluster (A)  502  may host a replicated storage virtual machine (B 1 -DR)  510  corresponding to a replication of the storage virtual machine (B 1 )  522 , which may provide failover access to replicated user data in the event the storage cluster (B)  504  experiences a disaster. 
       FIG. 5A  illustrates the storage virtual machine (A 2 )  514  actively serving clients with access to user data of the storage aggregate (A 2 ) stored within the second set of storage devices  534  (e.g., from within storage devices hosted at the storage cluster (A)  502 , and where data is replicated to mirrored storage devices hosted at the storage cluster (B)  504 ) while the storage cluster (A)  502  has ownership  540  of the second set of storage devices  534  and the storage aggregate (A 2 ). 
       FIG. 5B  illustrates a disaster  550  occurring at the storage cluster (A)  502 . The storage controller (A 2 )  516  may be inoperable for providing clients with access to user data through the storage aggregate (A 2 ) of the storage virtual machine (A 2 )  514  because of the disaster  550 . Accordingly, the relocation component  501  may perform a temporary switchover of ownership of the storage aggregate (A 2 ) from the storage cluster (A)  502  to the storage cluster (B)  504  based upon a disaster recovery relationship between the storage cluster (A)  502  and the storage cluster (B)  504 .  FIG. 5C  illustrates the relocation component  501  switching ownership  540 B of the second set of storage devices  534  of the storage aggregate (A 2 ) from the storage cluster (A)  502  to the storage cluster (B)  504 .  FIG. 5D  illustrates the relocation component  501  switching ownership of the storage aggregate (A 2 ) from the storage cluster (A)  502  to the storage cluster (B)  504 , which is illustrated by the second set of storage devices  534  having the slanted line fill, as opposed to the dotted fill, to illustrate ownership by the storage cluster (B)  504 .  FIG. 5E  illustrates the relocation component  501  switching the replicated storage virtual machine (A 2 -DR)  524  from a dormant state to an active state (e.g., where the replicated storage virtual machine (A 2 -DR)  524  may remain to be owned by the storage cluster (A)  502 ) for providing failover client access to the storage aggregate (A 2 ) that is temporarily owned by the storage cluster (B)  504 . In this way, storage virtual machines may be switched over for failover operation to the storage cluster (B)  504  at a storage virtual machine level of granularity, which may improve a recovery time object (RTO) because merely some, but not all, of storage could be switched over in response to the disaster  550 , for example. 
       FIG. 5F  illustrates the relocation component  501  determining that the storage cluster (A)  502  has recovered into an operational state from the disaster  550 . The relocation component  501  may switch the replicated storage virtual machine (A 2 -DR)  524  into the dormant state. The relocation component  501  may switch ownership of the storage aggregate (A 2 ) and the second set of storage devices  534  back from the storage cluster (B)  504  to the storage cluster (A)  502 . In this way, the relocation component  501  may perform a switchback of ownership to the first storage cluster  502 . 
     Still another embodiment involves a computer-readable medium comprising processor-executable instructions configured to implement one or more of the techniques presented herein. An example embodiment of a computer-readable medium or a computer-readable device that is devised in these ways is illustrated in  FIG. 6 , wherein the implementation  600  comprises a computer-readable medium  608 , such as a CD-R, DVD-R, flash drive, a platter of a hard disk drive, etc., on which is encoded computer-readable data  606 . This computer-readable data  606 , such as binary data comprising at least one of a zero or a one, in turn comprises a set of computer instructions  604  configured to operate according to one or more of the principles set forth herein. In some embodiments, the processor-executable computer instructions  604  are configured to perform a method  602 , such as at least some of the exemplary method  300  of  FIG. 3 , for example. In some embodiments, the processor-executable instructions  604  are configured to implement a system, such as at least some of the exemplary system  400  of  FIGS. 4A-4D  and/or at least some of the exemplary system  500  of  FIGS. 5A-5F , for example. Many such computer-readable media are contemplated to operate in accordance with the techniques presented herein. 
     It will be appreciated that processes, architectures and/or procedures described herein can be implemented in hardware, firmware and/or software. It will also be appreciated that the provisions set forth herein may apply to any type of special-purpose computer (e.g., file host, storage server and/or storage serving appliance) and/or general-purpose computer, including a standalone computer or portion thereof, embodied as or including a storage system. Moreover, the teachings herein can be configured to a variety of storage system architectures including, but not limited to, a network-attached storage environment and/or a storage area network and disk assembly directly attached to a client or host computer. Storage system should therefore be taken broadly to include such arrangements in addition to any subsystems configured to perform a storage function and associated with other equipment or systems. 
     In some embodiments, methods described and/or illustrated in this disclosure may be realized in whole or in part on computer-readable media. Computer readable media can include processor-executable instructions configured to implement one or more of the methods presented herein, and may include any mechanism for storing this data that can be thereafter read by a computer system. Examples of computer readable media include (hard) drives (e.g., accessible via network attached storage (NAS)), Storage Area Networks (SAN), volatile and non-volatile memory, such as read-only memory (ROM), random-access memory (RAM), EEPROM and/or flash memory, CD-ROMs, CD-Rs, CD-RWs, DVDs, cassettes, magnetic tape, magnetic disk storage, optical or non-optical data storage devices and/or any other medium which can be used to store data. 
     Although the subject matter has been described in language specific to structural features or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing at least some of the claims. 
     Various operations of embodiments are provided herein. The order in which some or all of the operations are described should not be construed to imply that these operations are necessarily order dependent. Alternative ordering will be appreciated given the benefit of this description. Further, it will be understood that not all operations are necessarily present in each embodiment provided herein. Also, it will be understood that not all operations are necessary in some embodiments. 
     Furthermore, the claimed subject matter is implemented as a method, apparatus, or article of manufacture using standard applicationming or engineering techniques to produce software, firmware, hardware, or any combination thereof to control a computer to implement the disclosed subject matter. The term “article of manufacture” as used herein is intended to encompass a computer application accessible from any computer-readable device, carrier, or media. Of course, many modifications may be made to this configuration without departing from the scope or spirit of the claimed subject matter. 
     As used in this application, the terms “component”, “module,” “system”, “interface”, and the like are generally intended to refer to a computer-related entity, either hardware, a combination of hardware and software, software, or software in execution. For example, a component includes a process running on a processor, a processor, an object, an executable, a thread of execution, an application, or a computer. By way of illustration, both an application running on a controller and the controller can be a component. One or more components residing within a process or thread of execution and a component may be localized on one computer or distributed between two or more computers. 
     Moreover, “exemplary” is used herein to mean serving as an example, instance, illustration, etc., and not necessarily as advantageous. As used in this application, “or” is intended to mean an inclusive “or” rather than an exclusive “or”. In addition, “a” and “an” as used in this application are generally be construed to mean “one or more” unless specified otherwise or clear from context to be directed to a singular form. Also, at least one of A and B and/or the like generally means A or B and/or both A and B. Furthermore, to the extent that “includes”, “having”, “has”, “with”, or variants thereof are used, such terms are intended to be inclusive in a manner similar to the term “comprising”. 
     Many modifications may be made to the instant disclosure without departing from the scope or spirit of the claimed subject matter. Unless specified otherwise, “first,” “second,” or the like are not intended to imply a temporal aspect, a spatial aspect, an ordering, etc. Rather, such terms are merely used as identifiers, names, etc. for features, elements, items, etc. For example, a first set of information and a second set of information generally correspond to set of information A and set of information B or two different or two identical sets of information or the same set of information. 
     Also, although the disclosure has been shown and described with respect to one or more implementations, equivalent alterations and modifications will occur to others skilled in the art based upon a reading and understanding of this specification and the annexed drawings. The disclosure includes all such modifications and alterations and is limited only by the scope of the following claims. In particular regard to the various functions performed by the above described components (e.g., elements, resources, etc.), the terms used to describe such components are intended to correspond, unless otherwise indicated, to any component which performs the specified function of the described component (e.g., that is functionally equivalent), even though not structurally equivalent to the disclosed structure. In addition, while a particular feature of the disclosure may have been disclosed with respect to only one of several implementations, such feature may be combined with one or more other features of the other implementations as may be desired and advantageous for any given or particular application.