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Storage Virtualization

Storage virtualization is a concept and term used within computer science. In few words, virtualization is the pooling of physical storage from multiple network storage devices into what appears to be a single storage device that is managed from a central console. Specifically, storage systems may use virtualization concepts as a tool to enable better functionality and more advanced features within the storage system.

User Benefits
Non-disruptive data migration
One of the major benefits of abstracting the host or server from the actual storage is the ability to migrate data while maintaining concurrent I/O access.
The process of moving the physical location is known as data migration. Most implementations allow for this to be done in a non-disruptive manner, that is concurrently while the host continues to perform I/O to the logical disk (or LUN).
The host only knows about the logical disk (the mapped LUN) and so any changes to the meta-data mapping is transparent to the host. This means the actual data can be moved or replicated to another physical location without affecting the operation of any client. When the data has been copied or moved, the meta-data can simply be updated to point to the new location, therefore freeing up the physical storage at the old location.
Improved utilization
Utilization can be increased by virtue of the pooling, migration, and Thin Provisioning services.
When all available storage capacity is pooled, system administrators no longer have to search for disks that have free space to allocate to a particular host or server. A new logical disk can be simply allocated from the available pool, or an existing disk can be expanded.
Pooling also means that all the available storage capacity can potentially be used. In a traditional environment, an entire disk would be mapped to a host. This may be larger than is required, thus wasting space. In a virtual environment, the logical disk (LUN) is assigned the capacity required by the using host.
Storage can be assigned where it is needed at that point in time, reducing the need to guess how much a given host will need in the future. Using Thin Provisioning, the administrator can create a very large thin provisioned logical disk, thus the using system thinks it has a very large disk from day 1.
Storage Tiering
Storage tiering automates the placement and movement of data between different tiers (or classes) of storage, with each tier potentially comprising devices from multiple vendors.
From the cost perspective point of view, here you can better see the benefits. While your active data stay on performing and fast storage, like the one that uses solid-state drives, rarely accessed data will be automatically stored on cheap hardware, based on policies. Policies can be made based on time, access frequency and file type.
Storage virtualization is a technology that helps organization to become Green, by better storage utilization.

Business impact
The main advantage in implementing a storage virtualization project is that an organization can rely on all storage systems from his infrastructure.
Every time when an application is implemented, a storage resource has to be allocated and certain SLA should be fulfilled.
Since the virtualization layer acts like a proxy between users and application and storage pool, resources can be allocated by specific needs: you need fast storage for an intensive I/O application, you get it, no matter what lays behind the proxy. Obviously, your organization should have fast storage inside. With help from virtualization layer, resources are used accordingly with business needs, to maximize the costs and improve efficiency.

Products supporting this technology

Storage systems can provide either block accessed storage, or file accessed storage. Block access is typically delivered over Fibre Channel, iSCSI, SAS, FICON or other protocols. File access is often provided using NFS or CIFS protocols.
Within the context of a storage system, there are two primary types of virtualisation that can occur:
- Block Virtualization 
- File Virtualization

Block virtualization used in this context refers to the separation of logical storage from physical storage so that it may be accessed without regard to physical storage or heterogeneous structure. This separation allows the administrators of the storage system greater flexibility in how they manage storage for end users.
Block virtualization is best summed up by Storage Area Network (SAN) and Network Attached Storage (NAS) technologies: distributed storage networks that appear to be single physical devices.

File-level virtualization addresses the NAS challenges by eliminating the dependencies between the data accessed at the file level and the location where the files are physically stored. This provides opportunities to optimize storage utilization and server consolidation and to perform non disruptive file migrations. Block virtualization is best summed up by Storage Area Network (SAN) and Network Attached Storage (NAS) technologies: distributed storage networks that appear to be single physical devices.
File virtualization moves the virtual layer up into the more human-consumable file and directory structure level. Most file virtualization technologies sit in front of storage networks and keep track of which files and directories reside on which storage devices, maintaining global mappings of file locations.