Storage virtualization

In computer science, storage virtualization uses virtualization to enable better functionality and more advanced features in computer data storage systems.

Broadly speaking, a "storage system" is also known as a storage array or disk array or a filer. Storage systems typically use special hardware and software along with disk drives in order to provide very fast and reliable storage for computing and data processing. Storage systems are complex, and may be thought of as a special purpose computer designed to provide storage capacity along with advanced data protection features. Disk drives are only one element within a storage system, along with hardware and special purpose embedded software within the system.

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 or SMB protocols.

Within the context of a storage system, there are two primary types of virtualization that can occur:

virtualization of storage helps achieve location independence by abstracting the physical location of the data. The virtualization system presents to the user a logical space for data storage and handles the process of mapping it to the actual physical location.

It is possible to have multiple layers of virtualization or mapping. It is then possible that the output of one layer of virtualization can then be used as the input for a higher layer of virtualization. Virtualization maps space between back-end resources, to front-end resources. In this instance, "back-end" refers to a logical unit number (LUN) that is not presented to a computer, or host system for direct use. A "front-end" LUN or volume is presented to a host or computer system for use.

The actual form of the mapping will depend on the chosen implementation. Some implementations may limit the granularity of the mapping which may limit the capabilities of the device. Typical granularities range from a single physical disk down to some small subset (multiples of megabytes or gigabytes) of the physical disk.

In a block-based storage environment, a single block of information is addressed using a LUN identifier and an offset within that LUN – known as a logical block addressing (LBA).

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