Storage virtualization: How, what and why

Corporate marketers have discovered – and are busily hyping – the concept of ‘virtualization’. But the precise definition of ‘storage virtualization’ depends very much on who’s using the term. Because storage virtualization sets the foundation for the enterprise storage utility, it’s crucial for business IT planners to understand its first principles, and not be fooled by the hype.

Virtualization separates the representation of storage to the server operating system from actual physical storage. This division of physical storage devices from the logical storage space presented to users and applications turns storage into a generally available utility pool.

Virtualization fulfils a role for storage similar to that which an operating system does for a computer system – namely, making programming and operation simpler by automating resource management ‘housekeeping’. When this process occurs, computer users are said to be ‘viewing its resources at a higher level of abstraction.’ Thus, in short, virtualization is the abstraction of storage.

This concept – and process – has great potential benefits for storage administration because it dramatically increases the amount of storage an administrator can manage in the same amount of time, or slashes the work necessary to manage the same amount of storage. But there’s one glitch: virtualization that will meet this goal of abstraction and serve as the key enabler for policy-based storage management at the highest strategic level is not yet widely available. Vendors recognize the importance of virtualization and have been sharing their roadmaps for product delivery. Most important to customers: the approach the vendors take, and when the solutions are delivered.

How Is It Done?

Storage virtualization hardware and/or software automatically maintain a set of tables (or other control structure) that maps the logical storage space that applications need to the physical storage actually available to the system. When logical-to-physical mapping occurs while applications are running – just as virtual memory operates in a PC – the storage virtualization is dynamic.

If the mapping is based on a simple rule, or algorithm – so that the storage available to an application is only provided preplanned, and not while the application is running – the storage virtualization is static. The relationship of dynamic storage virtualization and physical storage is analogous to virtual memory and RAM, because programmers do not need to think about memory requirements. Static virtual storage is to physical storage as memory overlays are to physical memory – users don’t have to think about program memory requirements as long as the programmers have.

Vendors are implementing storage virtualization in different ways – via varied architectures, or hardware and software (or mixed) approaches.

Virtualization can be implemented as: