Three Basic Categories for Storage Virtualization

Three basic categories for Storage Virtualization:
1. What is being virtualized
2. Where the virtualization occurs
3. How it is implemented.

What is being virtualized may include disks (cylinder, head, and sector virtualized into logical block addresses), blocks (logical blocks from disparate storage systems may be pooled into a common asset), tape systems (tape drives and tape systems may be virtualized into a single tape entity, or subdivided into multiple virtual entities), file systems (entire file systems may be virtualized into shared file systems), and file or record virtualization (files or records may be virtualized on different volumes). Where virtualization occurs may be on the host, in storage arrays, or in the network via intelligent fabric switches or SAN-attached appliances. How the virtualizaton occurs may be via in-band or out-of-band separation of control and data paths. While the taxonomy reflects the complexity of the subject matter, the common denominator of the various whats, wheres, and hows is that storage virtualization provides the means to build higher-level storage services that mask the complexity of all underlying components and enable automation of data storage operations.

The ultimate goal of storage virtualization should be to simplify storage administration. This can be achieved by a layered approach, binding multiple levels of technologies on a foundation of logical abstraction. Concealing the complexity of physical storage assets by only revealing a simplified logical view of storage is only a first step towards streamlining storage management. Treating multiple physical disks or arrays as a single logical entity segregates the user of storage capacity from the physical characteristics of disk assets, including physical location and unique requirements of the physical devices. Storage capacity for individual servers, however, must still be configured, assigned, and monitored by someone. Although one layer of complexity has been addressed, the logical abstraction of physical storage alone does not lift the burden of tedious manual administration from the shoulders of storage managers.

Source: Storage Virtualization: Technologies for Simplifying Data Storage and Management By Tom Clark