In the same way that server virtualisation builds a layer of abstraction above the physical servers, storage virtualisation does the same but does so above the layer of storage devices.
It is the pooling of physical storage from potentially multiple network storage devices into what appears to be a single storage device that is managed from a central console. Virtual storage, turns the disk drives of many, even disparate, storage devices into virtual disks.
For organisations who have islands of data scattered across different departments, storage virtualisation gives them the ability to view and manage multiple, networked heterogeneous storage devices as if they were a single pool of storage managed from a single console. To an operating system, the virtual storage appears as one device, regardless of the types of storage devices pooled. This also means that end enterprise-users find attaching or detaching extra storage to be easier.
As well as the operational benefits there are also substantial economic reasons why virtualisation is so appealing. Virtualised storage is not restricted by the capacity, speed or reliability limitations of the physical device that comprise them. Additionally with storage virtualisation, platform independent, software-based solutions eliminate the cost and price premiums of exclusive solutions. It brings the entire storage infrastructure to the highest level at the lowest cost because the solutions work on a variety of platforms, with a wide range of storage hardware.