Abstract:
A storage hypervisor having a software defined storage controller (SDSC) provides for a comprehensive set of storage control, virtualization and monitoring functions to decide the placement of data and manage functions such as availability, automated provisioning, data protection and performance acceleration. The SDSC running as a software driver on the server replaces the hardware storage controller function, virtualizes physical disks in a cluster into virtual building blocks and eliminates the need for a physical RAID layer, thus maximizing configuration flexibility for virtual disks. This configuration flexibility consequently enables the storage hypervisor to optimize the combination of storage resources, data protection levels and data services to efficiently achieve the performance, availability and cost objectives of individual applications. This invention enables complex SAN infrastructure to be eliminated without sacrificing performance, and provides more services than prior art SAN with fewer components, lower costs and higher performance.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims priority to U.S. Provisional Patent Application No. 61/690,201, filed on Jun. 21, 2012, entitled “STORAGE HYPERVISOR” which is incorporated by reference in its entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates generally to management of computer resources, and more specifically, to management of storage resources in data centers. 
         [0004]    2. Description of the Background Art 
         [0005]    A conventional datacenter typically includes three or more tiers (namely, a server tier, network tier and a storage tier) consisting of physical servers (sometimes referred to as nodes), network switches, storage systems and two or more network protocols. The server tier typically includes multiple servers that are dedicated to each application or application portion. Typically, these servers provide a single function (e.g., file server, application server, backup server, etc.) to one or more client computers coupled through a communication network. A server hypervisor, also known as a virtual machine monitor (VMM) is utilized on most servers. The VMM performs server virtualization to increase utilization rates for server resources and provide management flexibility by de-coupling servers from the physical computer hardware. Server virtualization enables multiple applications, each in an individual virtual machine, to run on the same physical computer. The provides significant cost savings since fewer physical computers are required to support the same application workload. 
         [0006]    The network tier is composed of a set of network segments connected by network switches. The network tier typically includes a communication network used by client computers to communicate with servers and for server-to-server communication in clustered applications. The network tier also includes a separate, dedicated storage area network (hereinafter “SAN”) to connect servers to storage systems. The SAN provides a high performance, low latency network to support input/output requests from applications running on servers to storage systems housing the application data. The communication network and storage area network or SAN typically run different network protocols requiring different skill sets and people with the proper training to manage each network. 
         [0007]    The storage tier typically includes a mix of storage systems based on different technologies including network attached storage (hereinafter “NAS”), block based storage and object based storage devices (hereinafter “OSD”). NAS systems provide file system services through a specialized network protocols while block based storage typically presents storage to servers as logical unit numbers (LUNs) utilizing some form of SCSI protocol. OSD systems typically provide access to data through a key-value pair approach which is highly scalable. The various storage systems include physical disks which are used for permanent storage of application data. The storage systems add data protection methods and services on top of the physical disks using data redundancy techniques (e.g. RAID, triple copy) and data services (e.g. snapshots and replication). Some storage systems support storage virtualization features to aggregate the capacity of the physical disks within the storage system into a centralized pool of storage resources. Storage virtualization provides management flexibility and enables storage resources to be utilized to create virtual storage on demand for applications. The virtual storage is accessed by applications running on servers connected to the storage systems through the SAN. 
         [0008]    When initially conceived, SAN architectures connected non-virtualized servers to storage systems which provided RAID data redundancy or were simple just-a-bunch of disks (JBOD) storage systems. Refresh cycles on servers and storage systems were usually three to five years and it was rare to repurpose systems for new applications. As the pace of change grew in IT datacenters and CPU processing density significantly increased, virtualization techniques were introduced at both the server and storage tiers. The consolidation of servers and storage through virtualization brought improved economy to the IT datacenters but it also introduced a new layer of management and system complexity. 
         [0009]    Server virtualization creates challenges for SAN architectures. SAN-based storage systems typically export a single logical unit number (LUN) shared across multiple virtual machines on a physical server, thereby sharing capacity, performance, RAID levels and data protection methods. This lack of isolation amplifies performance issues and makes managing application performance a tedious, manual and time consuming task. The alternative approach of exporting a single LUN to each virtual machine results in very inefficient use of storage resources and is operationally not feasible in terms of costs. 
         [0010]    While server virtualization adds flexibility and scalability, it also exposes an issue with traditional storage system design with rigid storage layers. Resources in current datacenters may be reconfigured from time to time depending on the changing requirements of the applications used, performance issues, reallocation of resources, and other reasons. A configuration change workflow typically involves creating a ticket, notifying IT staff, and deploying personnel to execute the change. The heavy manual involvement can be very challenging and costly for large scale data centers built on inflexible infrastructures. The rigid RAID and storage virtualization layers of traditional storage systems makes it difficult to reuse storage resources. Reusing storage resources require deleting all virtual disks, storage virtualization layers and RAID arrays before the physical disk resources can be reconfigured. Planning and executing storage resource reallocation becomes a manual and labor intensive process. This lack of flexibility also makes it very challenging to support applications that require self-provisioning and elasticity, e.g. private and hybrid clouds. 
         [0011]    Within the storage tier, additional challenges arise from heterogeneous storage systems from multiple vendors on the same network. This results in the need to manage isolated silos of storage capacity using multiple management tools. Isolated silos means that excess storage capacity in one storage system cannot flexibly be shared with applications running off storage capacity on a different storage system resulting in inefficient storage utilization, as well as, operational complexity. Taking advantage of excess capacity in a different storage system requires migrating data. 
         [0012]    Previous solutions attempt to address the issues of performance, flexibility, manageability and utilization at the storage tier through a storage hypervisor approach. It should be noted that storage hypervisors operate as a virtual layer across multiple heterogeneous storage systems on the SAN to improve their availability, performance and utilization. The storage hypervisor software virtualizes the individual storage resources it controls to create one or more flexible pools of storage capacity. Within a SAN based infrastructure, storage hypervisor solutions are delivered at the server, network and storage tier. Server based solutions include storage hypervisor delivered as software running on a server as sold by Virsto (US 2010/0153617), e.g. Virsto for vSphere. Network based solutions embed the storage hypervisor in a SAN appliance as sold by IBM, e.g. SAN Volume Controller and Tivoli Storage Productivity Center. Both types of solutions abstract heterogeneous storage systems to alleviate management complexity and operational costs but are dependent on the presence of a SAN and on data redundancy, e.g. RAID protection, delivered by storage systems. Storage hypervisor solutions are also delivered within the storage controller at the storage layer as sold by Hitachi (U.S. Pat. No. 7,093,035), e.g. Virtual Storage Platform. Storage hypervisors at the storage system abstract certain third party storage systems but not all. While data redundancy is provided within the storage system, the solution is still dependent on the presence of a SAN. There is no comprehensive solution that eliminates the complexity and cost of a SAN, while providing the manageability, performance, flexibility and data protection in a single solution. 
       SUMMARY OF THE INVENTION 
       [0013]    A storage hypervisor having a software defined storage controller (SDSC) of the present invention provides for a comprehensive set of storage control and monitoring functions, through virtualization to decide the placement of data and orchestrate workloads. The storage hypervisor manages functions such as availability, automated provisioning, data protection and performance acceleration services. A module of the storage hypervisor, the SDSC running as a software driver on the server replaces the storage controller function within a storage system on a SAN based infrastructure. A module of the SDSC, the distributed disk file system module (DFS) virtualizes physical disks into building blocks called chunks which are regions of physical disks. The novel approach of the SDSC enables the complexity and cost of the SAN infrastructure and SAN attached storage systems to be eliminated while greatly increasing the flexibility of a data center infrastructure. The unique design of the SDSC also enables a SAN free infrastructure without sacrificing the performance benefits of a traditional SAN based infrastructure. Modules of the SDSC, the storage virtualization module (SV) and the data redundancy module (DR) combine to eliminate the need for a physical RAID layer. The elimination of the physical RAID layer enables de-allocated virtual disks to be available immediately for reuse without first having to perform complicated and time consuming steps to release physical storage resources. The elimination of the physical RAID layer also enables the storage hypervisor to maximize configuration flexibility for virtual disks. This configuration flexibility enables the storage hypervisor to select and optimize the combination of storage resources, data protection levels and data services to efficiently achieve the performance, availability and cost objectives of each application. With the ability to present uniform virtual devices and services from dissimilar and incompatible hardware in a generic way, the storage hypervisor makes the hardware interchangeable. This enables continuous replacement and substitution of the underlying physical storage to take place without altering or interrupting the virtual storage environment that is presented. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    The invention is illustrated by way of example, and not by way of limitation in the figures of the accompanying drawings in which like reference numerals are used to refer to similar elements. 
           [0015]      FIG. 1  is a high-level block diagram illustrating a prior art system based on a storage area network infrastructure; 
           [0016]      FIG. 2  is a block diagram illustrating prior art example of a storage system presenting a virtual disk which is shared by multiple virtual machines on a physical server; 
           [0017]      FIG. 3  is another high-level block diagram illustrating a prior art system based on a storage area network infrastructure wherein the storage hypervisor is located in the server; 
           [0018]      FIG. 4  is yet another high-level block diagram illustrating a prior art system based on a storage area network infrastructure wherein the storage hypervisor is located in the network; 
           [0019]      FIG. 5  is yet still another high-level block diagram illustrating a prior art system based on a storage area network infrastructure wherein the storage hypervisor is located in the storage system; 
           [0020]      FIG. 6  is a high-level block diagram illustrating a system having a storage hypervisor located in the server with the network tier simplified and the storage tier removed according to one embodiment of the invention; 
           [0021]      FIG. 7  is a high-level block diagram illustrating modules within the storage hypervisor and both storage hypervisors configured for cache mirroring according to one embodiment of the invention; 
           [0022]      FIG. 8  is a block diagram illustrating modules of a software defined storage controller according to one embodiment of the invention; 
           [0023]      FIG. 9  is a block diagram illustrating an example of chunk (region of a physical disk) allocation for a virtual disk across nodes in a cluster (set of nodes that share certain physical disks on a communications network) and a direct mapping function of the virtual machine to a virtual disk according to one embodiment of the invention. 
           [0024]      FIG. 10  is a diagram illustrating an example of a user screen interface for automatically configuring and provisioning virtual machines according to one embodiment of the invention; 
           [0025]      FIG. 11  is a diagram illustrating an example of a user screen interface for automatically configuring and provisioning virtual disks according to one embodiment of the invention; and 
           [0026]      FIG. 12  is a diagram illustrating an example of a user screen interface for monitoring and managing the health and performance of virtual machines according to one embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0027]    Referring to  FIGS. 1 ,  3 ,  4  and  5  there is shown a high-level block diagram illustrating prior art systems based on a SAN infrastructure. The environment comprises multiple servers  10   a - n  and storage systems  20   a - n . The servers are connected to the storage systems  20   a - n  via a storage network  42 , such as a storage area network (SAN), Internet Small Computer System Interface (iSCSI), Network-attached storage (NAS) or other storage networks known to those of ordinary skill in the software or computer arts. Storage systems  20   a - n  comprises one or more homogeneous or heterogeneous computer storage devices. 
         [0028]    Turning once again to  FIGS. 1 ,  3 ,  4  and  5  (prior art), the servers  10   a - n  have corresponding physical computers  11   a - n  each which may incorporate such resources as CPUs  17   a - n , memory  15   a - n  and I/O adapters  19   a - n . The resources of the physical computers  11   a - n  are controlled by corresponding virtual machine monitors (VMMs)  18   a - n  that create and control multiple isolated virtual machines (VMs)  16   a - n ,  116   a - n  and  216   a - n . VMs  16   a - n ,  116   a - n  and  216   a - n  have guest operating system (OS)  14   a - n ,  114   a - n  and  214   a - n  and one or more software applications  12   a - n ,  112   a - n  and  212   a - n . Each VM  16   a - n ,  116   a - n  and  216   a - n  has one or more block devices (not shown) which are partitions of virtual disks (vDisks)  26   a - n ,  126   a - n  and  226   a - n  presented across the SAN by storage systems  20   a - n . The storage systems  20   a - n  has physical storage resources such as physical disks  22   a - n  and incorporates Redundant Array of Independent Disks (RAID)  24   a - n  to make stored data redundant. The storage systems  20   a - n  typically allocate one or more physical disks  22   a - n  as spare disks  21   a - n  for rebuild operations in event of a physical disk  22   a - n  failure. The storage systems  20   a - n  has corresponding storage virtualization layers  28   a - n  that provide virtualization and storage management functions to create vDisks  26   a - n ,  126   a - n  and  226   a - n . The storage systems  20   a - n  selects one or more vDisks  26   a - n ,  126   a - n  and  226   a - n  and present them as logical unit numbers (LUNs) to servers  10   a - n . The LUN is recognized by an operating system as a disk. 
         [0029]    Referring now to  FIG. 2  is a high-level block diagram illustrating prior art example of a storage system  20  presenting vDisks  26   a - n  to a server  10 . The vDisks  26   a - n  is an abstraction of the underlying physical disks  22  within the storage system  20 . Each VM  16   a - n  has one or more block devices (not shown) which are partitions of the vDisk  26   a - n  presented to the server  10 . Since the vDisk  26   a - n  provides shared storage to the VMs  16   a - n , and by extension to corresponding guest OS  14   a - n  and application  12   a - n , the block devices (not shown) for each VM  16   a - n , guest OS  14   a - n  and application  12   a - n  consequentially share the same capacity, the same performance, the same RAID levels and the same data service policies associated with vDisk  26   a - n.    
         [0030]    Referring now to  FIG. 3  there is shown a high-level block diagram illustrating a prior art system based on SAN infrastructure wherein the storage hypervisor  43   a - n  is located in the server  10   a - n . The storage hypervisor  43   a - n  provide virtualization and management services for a subset or all of the storage systems  20   a - n  on storage network  42  and typically rely on storage systems  20   a - n  to provide data protection services. 
         [0031]    Referring now to  FIG. 4  there is shown a high-level block diagram illustrating a prior art system based on SAN infrastructure wherein the storage hypervisor  45  is located in a SAN appliance  44  on storage network  42 . The storage hypervisor  45  provides virtualization and management services for a subset or all of the storage systems  20   a - n  on storage network  42  and typically rely on storage systems  20   a - n  to provide data protection services. 
         [0032]    Referring now to  FIG. 5  there is shown a high-level block diagram illustrating a prior art system based on SAN infrastructure wherein the storage hypervisor  47  is located in a storage system  20  on storage network  42 . The storage hypervisor  47  provides virtualization and management services for internal physical disks  22  and for external storage systems  46   a - n  directly attached to storage system  20 . 
         [0033]    Referring now to  FIG. 6  is a block diagram illustrating a system having our storage hypervisors  28   a ′- n ′ located in servers  10   a ′- n ′ with the network tier simplified and the storage tier removed according to one embodiment of the invention. The environment comprises multiple servers (nodes)  10   a ′- n ′ connected to each other via communications network  48 , such as Ethernet, InfiniBand and other networks known to those of ordinary skills in the art. An embodiment of the invention may split the communications network  48  into a client (not shown) to server  10   a ′- n ′ network and a server  10   a ′- n ′ to server  10   a ′- n ′ network by utilizing one or more network adapters on the servers  10   a ′- n ′. Such an embodiment may also have a third network adapter dedicated to system management. Communications network  48  may have one or more clusters which are sets of nodes  10   a ′- n ′ that share certain physical disks  28   a ′- n ′ on communications network  48 . In this invention, our storage hypervisor  28   a ′- n ′ virtualizes certain physical disks  28   a ′- n ′ on communications network  48  through a distributed disk file system (as will be described below). Virtualizing the physical disks  28   a ′- n ′ and using the resulting chunks (as will be described below) as building blocks enables the invention to eliminate the need for spare physical disks  21   a - n  ( FIG. 1 ) as practiced in prior art. Our storage hypervisor  28   a ′- n ′ also incorporates the functions of a hardware storage controller as software running on nodes  10   a ′- n ′. The invention thus enables the removal of the SAN and consolidates the storage tier into the server tier resulting in dramatic reduction in the complexity and cost of the system  60 . 
         [0034]    Also in  FIG. 6 , the nodes  10   a ′- n ′ have corresponding physical computers  11   a ′-n′ which incorporate such resources as CPUs  17   a ′- n ′, memory  15   a ′- n ′, I/O adapters  19   a ′- n ′ and physical disks  22   a ′- n ′. The CPUs  17   a ′- n ′, memory  15   a ′- n ′ and I/O adapters  19   a ′- n ′ resources of the physical computers  11   a ′-n′ are controlled by corresponding virtual machine monitors (VMMs)  18   a ′- n ′ that create and control multiple isolated virtual machines (VMs)  16   a ′- n ′,  116   a ′- n ′ and  216   a ′- n ′. VMs  16   a ′- n ′,  116   a ′- n ′ and  216   a ′- n ′ have guest OS  14   a ′- n ′,  114   a ′- n ′ and  214   a ′- n ′ and one or more software applications  12   a ′- n ′,  112   a ′- n ′ and  212   a ′- n ′. Nodes  10   a ′- n ′ run corresponding storage hypervisors  28   a ′- n ′. The physical disks  22   a ′- n ′ resources of physical computers  11   a ′-n′ are controlled by storage hypervisors  28   a ′- n ′ that create and control multiple vDisks  26   a ′- n ′,  126   a ′- n ′ and  226   a ′- n ′. The storage hypervisors  28   a ′- n ′ play a complementary role to the VMMs  18   a ′- n ′ by providing isolated vDisks  26   a ′- n ′,  126   a ′- n ′ and  226   a ′- n ′ for VMs  16   a ′- n ′,  116   a ′- n ′ and  216   a ′- n ′ which are abstractions of the physical disks  22   a ′- n ′. For each vDisk  26   a ′- n ′,  126   a ′- n ′ and  226   a ′- n ′, the storage hypervisor  28   a ′- n ′ manages a mapping list (as will be described below) that translates logical addresses in an input/output request from a VM  16   a ′- n ′,  116   a ′-n′ and  216   a ′- n ′ to physical addresses on underlying physical disks  22   a ′- n ′ in the communications network  48 . To create vDisks  26   a ′- n ′,  126   a ′- n ′ and  226   a ′- n ′, the storage hypervisor  28   a ′- n ′ requests unallocated storage chunks (as will be described below) from one or more nodes  10   a ′- n ′ in the cluster. By abstracting the underlying physical disks  22   a ′- n ′ and providing storage management and virtualization, data availability and data services in software, the storage hypervisor  28   a ′- n ′ incorporates functions of storage systems  20   a - n  ( FIG. 1 ) within physical servers  10   a ′- n ′. Adding new nodes  10   a ′- n ′ adds another storage hypervisor  28   a ′- n ′ to process input/output requests from VM  16   a ′- n ′,  116   a ′- n ′ and  216   a ′- n ′. The invention thus enables performance of the storage hypervisor  28   a ′- n ′ to scale linearly as new nodes  10   a ′- n ′ are added to the system  60 . By incorporating the functions of storage systems  20   a - n  ( FIG. 1 ) within physical servers  10   a ′- n ′, the storage hypervisor  28   a ′- n ′ directly presents local vDisks  26   a ′- n ′,  126   a ′- n ′ and  226   a ′- n ′ to VMs  16   a ′- n ′,  116   a ′- n ′ and  216   a ′- n ′ within nodes  10   a ′- n ′. This invention therefore eliminates the SAN  42  ( FIG. 1 ) as well as the network components needed to communicate between the servers  10   a - n  ( FIG. 1 ) and the storage systems  20   a - n  ( FIG. 1 ), such as SAN switches, host bus adapters (HBAs), device drivers for HBAs, and special protocols (e.g. SCSI) used to communicate between the servers  10   a - n  ( FIG. 1 ) and the storage systems  20   a - n  ( FIG. 1 ). The result is higher performance and lower latency for data reads and writes between the VMs  16   a ′- n ′,  116   a ′- n ′ and  216   a ′- n ′ and vDisks  26   a ′-n′,  126   a ′- n ′ and  226   a ′- n ′ within nodes  10   a ′- n′.    
         [0035]      FIG. 7  is a high-level block diagram illustrating modules within storage hypervisors  28   a ′ and  28   b ′ and both storage hypervisors  28   a ′ and  28   b ′ configured for cache mirroring according to one embodiment of the invention. In this invention, my storage hypervisor  28   a ′ comprises a data availability and protection module (DAP)  38   a , a persistent coherent cache (PCC)  37   a , a software defined storage controller (SDSC)  36   a , a block driver  32   a  and a network driver  34   a . Storage hypervisors  28   a ′ and  28   b ′ run on corresponding nodes  10   a ′ and  10   b ′. Storage hypervisor  28   a ′ presents the abstraction of physical disks  22   a ′- n ′ ( FIG. 6 ) as multiple vDisks  26   a ′- n ′ through a block device interface to VMs  16   a ′- n ′,  116   a ′- n ′ and  216   a ′- n ′ ( FIG. 6 ). 
         [0036]    Also in  FIG. 7 , DAP  38   a  provides data availability services to vDisk  26   a ′- n ′. The services include high availability services to prevent interrupted application operation due to VM  16   a ′- n ′,  116   a ′- n ′ and  216   a ′- n ′ ( FIG. 6 ) or node  10   a ′ failures. Snapshot services in DAP  38   a  provide protection against logical data corruption through point in time copies of data on vDisks  26   a ′- n ′. Replication services in DAP  38   a  provide protection against site failures by duplicating copies of data on vDisks  26   a ′- n ′ to remote locations or availability zones. DAP  38   a  provides encryption services to protect data against authorized access. Deduplication and compression services are also provided by DAP  38   a  to increase the efficiency of data storage on vDisks  26   a ′- n ′ and minimize the consumption of communications network  48  ( FIG. 6 ) bandwidth. The data availability and protection services may be automatically configured and/or manually configured through a user interface. Data services in DAP  38   a  may also be configured programmatically through a programming interface. 
         [0037]    Also in  FIG. 7 , PCC  37   a  performs data caching on input/output requests from VMs-n′,  116   a ′- n ′ and  216   a ′- n ′ ( FIG. 6 ) to enhance system responsiveness. The data may reside in different tiers of cache memory, including server system memory  15   a ′- n ′ ( FIG. 6 ), physical disks  22   a ′- n ′ or memory tiers within physical disks  22   a ′- n ′. Data from input/outputs requests are initially written to cache memory. The length of time data stays in cache memory is based on information gathered from analysis of input/output requests from VMs  16   a ′- n ′,  116   a ′- n ′ and  216   a ′- n ′ ( FIG. 6 ) and from system input. System input include information such as application type, guest OS, file system type, performance requirements or VM priority provided during creation of the VM  16   a ′- n ′,  116   a ′- n ′ and  216   a ′- n ′ ( FIG. 6 ). The information collected enables PCC  37   a  to perform application aware caching and efficiently enhance system responsiveness. Software modules of the PCC  37   a  may run on CPU  17   a ′- n ′ resources on the nodes  10   a ′- n ′ and/or within physical disks  22   a ′- n ′. There are some data called metadata (not shown) that are used to define ownership, to provide access, to control and to recover vDisks  26   a ′- n ′. Data for write requests to vDisks  26   a ′- n ′ and metadata changes for vDisks  26   a ′- n ′ on node  10   a ′ are mirrored by PCC  37   a  through an interlink  39  across the communications network  48  ( FIG. 6 ). The mirrored metadata provide the information needed to rapidly recover VMs  16   a ′- n ′,  116   a ′- n ′ and  216   a ′- n ′ ( FIG. 6 ) for operation on any node  10   a ′- n ′ in the cluster in the event of VM  16   a ′- n ′,  116   a ′- n ′ and  216   a ′- n ′ or node  10   a ′- n ′ failures. The ability to rapidly recover VMs  16   a ′- n ′,  116   a ′- n ′ and  216   a ′- n ′ ( FIG. 6 ) enable high availability services to support continuous operation of applications  12   a ′- n ′,  112   a ′- n ′ and  212   a ′- n ′ ( FIG. 6 ). 
         [0038]    Also in  FIG. 7 , SDSC  36   a  receives input/output requests from PCC  37   a . SDSC  36   a  translates logical addresses in input/output requests to physical addresses on physical disks  22   a ′- n ′ ( FIG. 6 ) and reads/writes data to the physical addresses. The SDSC  36   a  is further described in  FIG. 8 . The block driver  32   a  reads from and/or writes to storage chunks (as will be described below) based on the address space translation from SDSC  36   a . Input/output requests to remote nodes  10   a ′- n ′ ( FIG. 6 ) are passed through network driver  34   a.    
         [0039]      FIGS. 6 and 8  contain a block diagram illustrating modules of the SDSC  36  according to one embodiment of the invention. The SDSC  36  comprises a storage virtualization module (SV)  52 , a data redundancy module (DR)  56  and a distributed disk file system module (DFS)  58 . 
         [0040]    Also in  FIGS. 6 ,  8  and  9 , the DFS  58  module virtualizes and enables certain physical disk resources  22   a ′- n ′ in a cluster to be aggregated, centrally managed and shared across the communications network  48 . The DFS  58  implements metadata (not shown) structures to organize physical disk resources  22   a ′- n ′ of the cluster into chunks  68  of unallocated virtual storage blocks. The metadata (not shown) are used to define ownership, to provide access, to control and to perform recovery on vDisks  26   a ′- n ′,  126   a ′- n ′ and  226   a ′- n ′. The DFS  58  module supports an negotiated allocation scheme utilized by nodes  10   a ′- n ′ to request and dynamically allocate chunks  68  from any node  10   a ′- n ′ in the cluster. Chunks  68  that have been allocated to a node  10   a ′- n ′ are used as building blocks to create corresponding vDisks  26   a ′- n ′,  126   a ′- n ′ and  226   a ′- n ′ for the node  10   a ′- n ′. By virtualizing physical disks  22   a ′- n ′ into virtual building blocks, the DFS  58  module enables elastic usage of chunks  68 . Chunks  68  which have been allocated, written to and then de-allocated, may be immediately erased and released for reuse. This elasticity of chunk  68  allocation/de-allocation enables dynamic storage capacity balancing across nodes  10   a ′- n ′. Request for new chunks  68  may be allocated from nodes  10   a ′- n ′ which have more available capacity. The newly allocated chunks  68  are used to physically migrate data to the destination node  10   a ′- n ′. On completion of the data migration, chunks  68  from the source node  10   a ′- n ′ may be immediately released and added to the available pool of storage capacity. The elasticity extends to metadata management in the DFS  58  module. vDisks  26   a ′- n ′,  126   a ′- n ′ and  226   a ′- n ′ may be quickly migrated without data movement through metadata transfer and metadata update of vDisk  26   a ′- n ′,  126   a ′- n ′ and  226   a ′- n ′ ownership. With this approach, the DFS  58  module supports workload balancing among nodes  10   a ′- n ′ for CPU  17   a ′- n ′ resources and input/output requests load balancing across nodes  10   a ′- n ′. The DFS  58  module supports nodes  10   a ′- n ′ and physical disks  22   a ′- n ′ to be dynamically added or removed from the cluster. New nodes  10   a ′- n ′ or physical disks  22   a ′- n ′ added to the cluster are automatically registered by the DFS  58  module. The physical disks  22   a ′- n ′ added are virtualized and the DFS  58  metadata (not shown) structures are updated to reflect the added capacity. 
         [0041]    Also in  FIGS. 6 ,  8  and  9 , the SV  52  module presents a block device interface and performs translation of logical block addresses from input/output requests to logical addresses on chunks  68 . The SV  52  manages the address translation through a mapping list  23 . The mapping list  23  is used by the SV  52  module to logically concatenate chunks  68  and presents them as a contiguous virtual block storage device called a vDisk  26   a ′- n ′,  126   a ′- n ′ and  226   a ′- n ′ to VMs  16   a ′- n ′,  116   a ′- n ′ and  216   a ′- n ′. The SV  52  module enables vDisk  26   a ′- n ′,  126   a ′- n ′ and  226   a ′- n ′ to be created, expanded or deleted on demand automatically and/or configured through a user interface. Created vDisks  26   a ′- n ′,  126   a ′- n ′ and  226   a ′- n ′ are visible on communications network  48  and may be accessed by VMs  16   a ′- n ′,  116   a ′- n ′ and  216   a ′- n ′ in the system  60  that are granted access permissions. A reservation protocol is utilized to negotiate access to vDisks  26   a ′- n ′,  126   a ′- n ′ and  226   a ′- n ′ to maintain data consistency, privacy and security. vDisks  26   a ′- n ′,  126   a ′- n ′ and  226   a ′- n ′ ownership are assigned to individual nodes  10   a ′- n ′. Only nodes  10   a ′- n ′ with ownership of the vDisk  26   a ′- n ′,  126   a ′- n ′ and  226   a ′- n ′ can accept and process input/output requests and read/write data to chunks  68  on physical disks  22   a ′- n ′ which are allocated to the vDisk  26   a ′- n ′,  126   a ′- n ′ and  226   a ′- n ′. The vDisk  26   a ′- n ′,  126   a ′- n ′ and  226   a ′- n ′ operations are also configured programmatically through a programming interface. SV  52  also manages input/output performance metrics (latency, IOPS, throughput) per vDisk  26   a ′- n ′,  126   a ′- n ′ and  226   a ′- n ′. Any available chunk  68  from any node  10   a ′- n ′ in the cluster can be allocated and utilized to create a vDisk  26   a ′- n ′,  126   a ′- n ′ and  226   a ′- n ′. De-allocated chunks  68  may be immediately erased and available for reuse on new vDisks  26   a ′- n ′,  126   a ′- n ′ and  226   a ′- n ′ without complicated and time consuming steps to delete virtual disks  26   a - n ,  126   a - n  and  226   a - n  ( FIG. 1 ), storage virtualization  28   a - n  ( FIG. 1 ) layers and RAID  24   a - n  layers ( FIG. 1 ) layers as practiced in prior art. The invention enables this elasticity by adding data redundancy (as will be described below) as data are written to chunks  68 . The invention thus eliminates the need for rigid physical RAID  24   a - n  layer ( FIG. 1 ) as practiced in prior art. The SV  52  module supports a thin provisioning approach in creating and managing vDisks  26   a ′- n ′,  126   a ′- n ′ and  226   a ′- n ′. Chunks  68  are not allocated and added to the mapping list  23  for a vDisk  26   a ′- n ′,  126   a ′- n ′ and  226   a ′- n ′ until a write request is received to save data to the vDisk  26   a ′- n ′,  126   a ′- n ′ and  226   a ′- n ′. The thin provisioning approach enables logical storage resources to be provisioned for applications  12   a ′- n ′,  112   a ′- n ′ and  212   a ′- n ′ without actually committing physical disk  22   a ′- n ′ capacity. The invention enables the available physical disk  22   a ′- n ′ capacity in the system  60  to be efficiently utilized only for actual written data instead of committing physical disk  22   a ′- n ′ capacity which may or may not be utilized by applications  12   a ′- n ′,  112   a ′- n ′ and  212   a ′- n ′ in the future. 
         [0042]    Also in  FIGS. 6 ,  8  and  9 , in the preferred embodiment the DR  56  module provides data redundancy services to protect against hardware failures, such as physical disk  22   a ′- n ′ failures or node  10   a ′- n ′ failures. The DR  56  module utilizes RAID parity and/or erasure coding to add data redundancy. As write requests are received, the write data in the requests are utilized by the DR  56  module to compute parity or redundant data. The DR  56  module writes both the data and the computed parity or redundant data to chunks  68  which are mapped to physical addresses on physical disks  22   a ′- n ′. In the event of hardware failures such as media errors on physical disks  22   a ′- n ′, physical disk  22   a ′- n ′ failures or node  10   a ′- n ′ failures, redundant data is utilized to calculate and rebuild the data on failed physical disks  22   a ′-n′ or nodes  10   a ′- n ′. The rebuilt data are written to new chunks  68  allocated for the rebuild operation. Since the size of chunks  68  is much smaller than the capacity of physical disks  22   a ′- n ′, the time to compute parity and write the rebuilt data for chunks  68  is proportionately shorter. Compared to prior art, the invention significantly shortens the time to recover from hardware failures. By shortening the time for the rebuild operation, the invention greatly reduces the chance of losing data due to a second failure occurring prior to the rebuilding operation completing. By adding data redundancy to chunks  68 , the invention also eliminates the need for spare physical disks  21   a - n  ( FIG. 1 ) practiced in prior art. Compared to prior art, the invention further shortens the rebuilding time by enabling rebuilding operations on one or more nodes  10   a ′- n ′ onto one or more physical disks  22   a ′- n ′. The DR  56  module on each node  10   a ′- n ′ performs the rebuilding operation for corresponding vDisks  26   a ′- n ′,  126   a ′- n ′ and  226   a ′- n ′ on the node  10   a ′- n ′. Since the replacement chunk  68  for the rebuild operation may be allocated from one or more physical disks  22   a ′- n ′, the invention enables the rebuild operation to be performed in parallel on one or more nodes  10   a ′- n ′ onto one or more physical disks  22   a ′- n ′. This is much faster than a storage system  20   a - n  ( FIG. 1 ) performing a rebuild operation on one spare physical disk  22   a - n  ( FIG. 1 ) as practiced in prior art. Since the SV  52  module allocates and adds chunks  68  to mapping list  23  on write requests, rebuilding a vDisk  26 ′ is significantly faster compared to the prior art approach of rebuilding an entire physical disk  22   a ′- n ′ on hardware failures. By utilizing a thin provisioning approach, the rebuilding operation only has to compute parity and rebuild data for chunks  65 ,  66  and  67  with application data written. The invention encompasses the prior art approach of triple copy for data redundancy and provides a much more efficient redundancy approach. For example in the triple copy approach, chunks  65 ,  66  and  67  have identical data written. With this approach, only one third of the capacity is actually used for storing data. In one embodiment of the invention, a RAID parity approach enables chunks  65 ,  66  and  67  to be written with both data and computed parity. Both the data and computed parity are distributed among chunks  65 ,  66  and  67 . Compared to the triple copy approach, the RAID parity approach enables twice as much data to be written to chunks  65 ,  66  and  67 . The efficiency of data capacity can be further improved by increasing the number of chunks  68  used to distribute data. By utilizing RAID parity and/or erasure coding, the DR  56  module enables significantly more efficient data capacity utilization compared to the triple copy approach practiced in prior art. Since vDisks  26   a ′- n ′,  126   a ′- n ′ and  226   a ′- n ′ are created from chunks  68  allocated and accessed across the communications network  48 , the network bandwidth is also efficiently utilized compared to prior art practices. The DR  56  module enables the data redundancy type to be selectable per vDisk  26   a ′- n ′,  126   a ′- n ′ and  226   a ′- n ′. The data redundancy type may be automatically and/or manually configured through a user interface. The data redundancy type is also configurable programmatically through a programming interface. 
         [0043]      FIG. 9  is a diagram illustrating an example of chunk (region of a physical disk) allocation for a vDisk  26 ′ across nodes  10   a ′- n ′ in a cluster (set of nodes that share certain physical disks on a communications network) and a direct mapping function  27  of the virtual machine  16 ′ to a virtual disk  26 ′ and consequently to chunks  65 ,  66  and  67  on physical disks  22   a ′- n ′ according to one embodiment of the invention. One vDisk  26 ′ with three allocated chunks  65 ,  66  and  67  is illustrated for purposes of simplification. The SV  52  ( FIG. 8 ) module allocates chunks  68  from nodes  10   a ′- n ′ in the cluster through an negotiated allocation scheme. A mapping list  23  is used by the SV  52  ( FIG. 8 ) module to logically concatenate chunks  68  and presents them as a contiguous virtual block storage device called a vDisk  26 ′ to VM  16 ′. Write data from VM  16 ′ to vDisk  26 ′ are used by the DR  56  module ( FIG. 8 ) to compute parity and add data redundancy. The physical addresses for the write data and computed parity or redundant data are translated from the mapping list  23 . The write data from VM  16 ′ and the computed parity or redundant data are written by the DR  56  module ( FIG. 8 ) to translated addresses for chunks  65 ,  66  and  67  in mapping list  23 . This invention enables the SV  52  module ( FIG. 8 ) to select the data redundancy type independently for each vDisk  26 ′. In contrast with the consequential sharing of capacity, performance, RAID levels and data service policies of prior art ( FIG. 2 ), the ability to independently select data redundancy type maximizes configuration flexibility and isolation between vDisk  26 ′. Each vDisk  26 ′ is provided with the capacity, performance, data redundancy protection and data service policies that matches the needs of the application  12 ′ corresponding to VM  16 ′. The configurable performance parameters include the maximum number of input/output operations per second, the priority at which input/output requests for the vDisks  26 ′ will be processed and the locking of allocated chunks  65 ,  66  and  67  to the highest performance storage tier, such as SSD. The configurable data service policies include enabling services such as snapshot, replication, encryption, deduplication, compression and data persistence. Services such as snapshot support additional configuration parameters including the time of snapshot, snapshot period and the maximum number of snapshots. Additional configuration parameters for encryption services include the type of encryption. With system input on application type, VM  16 ′ may be automatically provisioned and managed according to its application  12 ′ and/or guest OS  14 ′ unique requirements without impact to adjacent VMs  16   a ′- n ′,  116   a ′- n ′ and  216   a ′- n ′ ( FIG. 6 ). An example of such system input is illustrated in  FIGS. 10 and 11  where the user selects the type of application and computing environment they want on their VM  16   a ′- n ′,  116   a ′- n ′ and  216   a ′- n ′ ( FIG. 6 ). The isolation between vDisks  26 ′ also enables simple performance reporting and tuning for each vDisk  26 ′ and its corresponding VM  16 ′, guest OS  14 ′ and application  12 ′. Performance demanding VMs  16   a ′-n′,  116   a ′- n ′ and  216   a ′- n ′ ( FIG. 6 ) generating increased IOPS or throughput may be quickly identified and/or managed. An example of such a user interface and reporting tool is illustrated in  FIG. 12 . The invention thus provides more valuable information, greater flexibility and a higher degree of control at the VM  16   a ′- n ′,  116   a ′- n ′ and  216   a ′- n ′ ( FIG. 6 ) level compared to the prior art illustrated in  FIG. 2 . 
         [0044]      FIG. 10  is a diagram illustrating an example of a user screen interface  80  for automatically configuring and provisioning VMs  16   a ′- n ′,  116   a ′- n ′ and  216   a ′- n ′ ( FIG. 6 ) according to one embodiment of the invention. The user screen interface  80  may include a number of functions  82  that allow the user to list the computing environment by operating systems, application type or user defined libraries. The user screen interface  80  may include a function  84  that allows the user to select a pre-configured virtual system. A user screen interface  80  may include a function  86  that allows the user to assign the level of computing resource for VMs  16   a ′- n ′,  116   a ′- n ′ and  216   a ′- n ′ ( FIG. 6 ). The computing resources may have different number of processors, processor speeds or memory capacity. Depending on the implementation, the user screen interface  80  may include additional, fewer, or different features than those shown. 
         [0045]      FIG. 11  is a diagram illustrating an example of a user screen interface  90  for automatically configuring and provisioning vDisks  26   a ′- n ′,  126   a ′- n ′ and  226   a ′- n ′ ( FIG. 6 ) according to one embodiment of the invention. The user screen interface  90  shows a pre-configured vDisk  92  associated with the application previously selected by the user. A function  98  may include options for the user to change the configuration. The user screen interface  90  shows data services selection  94  automatically configured according to the application previously selected by the user. The user screen interface  90  may include a function  96  that allows the user to change the pre-configured capacity. Depending on the implementation, the user screen interface  90  may include additional, fewer, or different features than those shown. 
         [0046]      FIG. 12  is a diagram illustrating an example of a user screen interface  100  for monitoring and managing the health and performance of VMs  16   a ′- n ′,  116   a ′- n ′ and  216   a ′- n ′ ( FIG. 6 ) according to one embodiment of the invention. The user screen interface  100  may include a number of functions  102  for changing the views of the user. The user screen interface  100  may present a view  104  to list the parameters and status of VMs that are assigned to a user account. The user screen interface  100  may include views  106  to present detailed performance metrics to the user. Depending on the implementation, the user screen interface  100  may include additional, fewer, or different features than those shown. 
         [0047]    As will be appreciated by one skilled in the art, aspects of the present invention may be embodied as a system, method or computer program product. Accordingly, aspects of the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, micro-code, etc.) or an embodiment combining software and hardware aspects that may all generally be referred to herein as a “circuit,” “module” or “system.”Furthermore, aspects of the present invention may take the form of a computer program product embodied in one or more computer readable medium(s) having computer readable program code embodied thereon. 
         [0048]    Any combination of one or more computer readable medium(s) may be utilized. The computer readable medium may be a computer readable storage medium. A computer readable storage medium may be, for example, but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. More specific examples (a non-exhaustive list) of the computer readable storage medium would include the following: an electrical connection having one or more wires, a portable computer diskette, a hard disk, a solid state drive (SSD), a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), an optical fiber, a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing. In the context of this document, a computer readable storage medium may be any tangible medium that can contain, or store a program for use by or in connection with an instruction execution system, apparatus, or device. 
         [0049]    Program code embodied on a computer readable medium may be transmitted using any appropriate medium, including but not limited to wireless, wireline, optical fiber cable, RF, etc., or any suitable combination of the foregoing. 
         [0050]    Computer program code for carrying out operations for aspects of the present invention may be written in any combination of one or more programming languages, including an object oriented programming language such as Java, Smailtalk, C++ or the like and conventional procedural programming languages, such as the “C” programming language or programming languages such as assembly language. 
         [0051]    Aspects of the present invention are described below with reference to block diagrams of methods, apparatus (systems) and computer program products according to embodiments of the invention. It will be understood that each block of the block diagrams, and combinations of blocks in the block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions/acts specified in the block diagram block or blocks. 
         [0052]    These computer program instructions may also be stored in a computer readable medium that can direct a computer, other programmable data processing apparatus, or other devices to function in a particular manner, such that the instructions stored in the computer readable medium produce an article of manufacture including instructions which implement the function/act specified in the block diagram block or blocks. 
         [0053]    The computer program instructions may also be loaded onto a computer, other programmable data processing apparatus, or other devices to cause a series of operational steps to be performed on the computer, other programmable apparatus or other devices to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide processes for implementing the functions/acts specified in the block diagram block or blocks. 
         [0054]    The block diagrams in  FIGS. 6 through 13  illustrate the architecture, functionality, and operation of possible implementations of systems, methods and computer program products according to various embodiments of the present invention. In this regard, each block in the block diagrams may represent a module, segment, or portion of code, which comprises one or more executable instructions for implementing the specified logical function(s). It should also be noted that, in some alternative implementations, the functions noted in the block may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each block of the block diagrams, and combinations of blocks in the block diagrams, can be implemented by special purpose hardware-based systems that perform the specified functions or acts, or combinations of special purpose hardware and computer instructions. 
         [0055]    The corresponding structures, materials, acts, and equivalents of all means or steps plus function elements in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of the present invention has been presented for purposes of illustration and description, but it is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention. The embodiment was chosen and described in order to best explain the principles of the invention and the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated.