Storage virtualization creates a layer of abstraction between the operating system and the physical disks used for data storage. The virtualized storage is then location-independent, which can enable more efficient storage use and better storage management.
For example, the storage virtualization software or device creates a logical space, and then manages metadata that establishes a map between the logical space and the physical disk space. The creation of logical space allows a virtualization platform to present storage volumes that can be created and changed with little regard for the underlying disks.
The most immediate benefit of storage virtualization is increased storage utilization, which can reduce wasted storage within the enterprise. For example, a logical unit number (LUN) provisioned on a storage area network (SAN) may allocate space that may not be used, or disks may be left unallocated -- lost and forgotten on storage arrays scattered across the data center. With virtualization, otherwise-unused storage can be cobbled together into viable LUNs and allocated to applications.
Data storage virtualization also supports migration and replication of LUNs between storage systems. This is particularly useful when one storage system must be taken offline for maintenance or replacement. By simply changing the mapping scheme, virtualization can move the location of data without disrupting disk I/O, allowing for efficient and nondisruptive data movement within an enterprise.
Storage management can be greatly simplified. Rather than managing multiple (often heterogeneous) storage subsystems, a virtualized storage environment can be managed through a single mechanism. In addition, advanced storage management techniques such as thin provisioning and dynamic provisioning can readily be supported. thin provisioning allows the creation of a LUN that is larger than the physical disk space allocated to it. For example, a 1 GB LUN can be created with perhaps 100 MB of storage space to start. As the associated application uses the disk space, more disk space can be allocated periodically (up to the assigned amount) without having to recreate the LUN.
Dynamic provisioning is similar, allowing the size of a LUN to be grown or shrunk as needed, ensuring the size of a LUN is always appropriate for each application. But traditional storage management (such as RAID group creation and maintenance) is still required.
Host-based storage virtualization such as Symantec's Veritas Storage Foundation uses device drivers and additional software to virtualize the physical disks within a host system. Device-based storage virtualization such as Hitachi Data Systems' Universal Storage Platform incorporates and manages virtualization within the storage array itself. Network-based storage virtualization uses a server (appliance) or smart switch like an EMC Invista within a Fibre Channel or iSCSI SAN to implement the abstraction between the network I/O and storage controllers.