Virtual Memory Operating Systems first arrived during the ’60s. Storage virtualization was pioneered on mainframes during the ’70s as virtualization concepts began to advance from the processor into storage subsystems. In the mid-70s, the original IBM 3850 Mass Storage System used virtualization to make a helical scan tape cartridge look like a disk drive to the mainframe operating system. The late ’70s witnessed the introduction of the first solid-state disk, a box of Dynamic Random Access Memory (DRAM) chips that appeared to the operating system as several rotating magnetic disks.

Virtualization reached a new level when the first Redundant Array of Inexpensive Disks (RAID) virtual disk array was announced in 1992 for mainframe systems. By combining data compression with virtualization, customers were able to store more data than the actual capacity of the array’s disk drives. Integrated virtual tape systems, which are disk arrays that serve as a front-end buffer for robotic tape libraries, first appeared in 1997 on mainframe systems. Storage Area networks (SAns) or switch virtualization appeared in the late ’90s for open systems but the seeds of this concept, called “shared DASD,” had been a mainframe staple for years. The Virtual Tape Library (VTL) concept, a derivative of the integrated VTL that had no physical tape, was introduced earlier this decade for open systems.

Storage Virtualization

Virtualization techniques are most commonly used when consolidating resources. The benefits of virtualization are vast and range from a reduction in software license fees to energy savings. Storage virtualization is an abstraction layer that overlays a large number of physical storage devices. With the steady proliferation of disk arrays and tape drives in and beyond the primary data center, managing these resources is a never-ending challenge. The abstraction possible with storage virtualization can mask the unique or proprietary features of each physical storage system and provide a common way of dealing with these disparate devices, ultimately easing storage management.

Storage virtualization also provides a more consistent user interface for all storage applications. A mainframe storage array from IBM, EMC, Sun, or Hitachi Data Systems comes with its own set of storage management applications such as replication, snapshots and mirroring, but the actual storage applications are implemented differently for each system. By adding storage virtualization on top of these different products, a single set of storage applications can be initiated, so there’s no need to learn multiple user interfaces to achieve the same function; this reduces management time and costs.

Storage virtualization is widely used in file systems, SANs, switches, disk arrays, and virtual tape systems on mainframe and open systems. Users can implement storage virtualization with host software, or hardware and software appliances. Highly cost-effective solutions such as tiered storage can be simplified when based on a virtualized storage environment.

Storage virtualization is now a rapidly maturing open systems technology and is beginning to traverse both mainframe and non-mainframe systems using a common interface. Long overdue, this commonality pushes IT in the direction that “you don’t have to be a platform or operating system expert; you just need to understand storage.” This gives the customer added leverage for coping with limited personnel resources and reduces overall complexity. Knowing how, when, and where to virtualize is critical to realizing these benefits and there are several options to carefully consider.

Four Options for Storage Virtualization

Businesses have four primary options for where they can implement the virtualization architecture:

• Virtualization is provided by software installed on the host or on all application hosts.

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