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Defining storage virtualization

The term storage virtualization has been with us since 1999, and the concept continues with new product offerings that are variations of the original.

The longevity of storage virtualization in a high tech world where new ideas gain a foothold rapidly is a testament to the value that storage virtualization delivers. But there are many descriptions for storage virtualization based on the variety of products and the desire of vendor marketing to distinguish their products. A quick review of what is encompassed by the general phrase “storage virtualization” might be useful to characterize these offerings and the context in which they are typically used.

First, let’s look at the descriptions of virtualization:

  • Grouping or pooling of resources for greater resource utilization.
  • Abstraction to enable storage management at a higher level. This includes the promised ability to automate actions across the virtualized resources and the ability to use the same management tools across heterogeneous devices.
  • Applying advanced features such as remote replication and point-in-time copies (snapshot) across the aggregated, abstracted resources without having to use multiple, device-specific capabilities.
  • Distribution of data to aid in performance.  This may be for parallel access or load balancing.
  • Transparent migration of data between LUNs and storage systems for purposes such as asset retirement, technology upgrades, and load and capacity balancing.

The different types for storage virtualization are depicted with this graphic:

There are preconceptions about the term storage virtualization that exist primarily because of the success of products and product marketing.  Most understand storage virtualization to be block virtualization where LUNs are presented to attached hosts that are constituted from multiple storage resources that may be from different storage systems and vendors.  The next preconception is that the block virtualization is done in-band (in the data path), which again comes from the success or predominance of those types of solutions.  There are several locations where the virtualization can occur either in-band or out-of-band.

The attachment of external storage systems/arrays by other storage systems (storage system-based virtualization) has been commonly deployed with many vendors under different names.  Using an appliance in the data path (in-band) is the most prevalent method of storage virtualization. And abstracting the access to the storage through software installed on servers is another approach that is usually out-of-band from the data access standpoint but is done through the control of where the access is targeted.

Confusion remains around storage virtualization as vendors try to highlight different characteristics their products bring to customers. Ultimately, storage virtualization is all about the value delivered.  It can affect the capital expense with greater resource utilization and greater performance.  It can have a measurable effect on the operational expense with management costs, licensing costs for advanced features, and the ability to transparently migrate data between systems.  IT must look beyond the labels applied to the solution and focus on the value the solution brings.

(Randy Kerns is Senior Strategist at Evaluator Group, an IT analyst firm).