The Economic Drivers for Storage Virtualization
"..Reduce costs without sacrificing data integrity or performance..."
Computer systems in general are highly complex, too complex, in fact, to be administered at a discrete physical level. As computer technology has evolved, a higher proportion of CPU cycle time has been dedicated to abstracting the underlying hardware, memory management, input/output, and processor requirements from the user interface. Today, a computer user does not have to be conversant in assembly language programming to make a change in a spreadsheet. The interface and management of the underlying technology has been heavily virtualized.
Storage administration, by contrast, is still tedious, manual-intensive, and seemingly never-ending. The introduction of storage networking has centralized storage administrative tasks by consolidating dispersed direct-attached storage assets into larger, shared resources on a SAN. Fewer administrators can now manage more disk capacity and support more servers, but capacity for each server must still be monitored, logical units manually created and assigned, zones established and exported, and new storage assets manually brought online to service new application requirements. In addition, although shared storage represents a major technological advance over direct-attached storage, it has introduced its own complexity in terms of implementation and support. Complexity equates to cost. Finding ways to hide complexity, automate tedious tasks, streamline administration, and still satisfy the requirements of high performance and data availability saves money, and that is always the bottom line. That is the promise of storage virtualization, although many solutions today are still far short of this goal.
Another highly advertised objective for storage virtualization is to overcome vendor interoperability issues. Storage array manufacturers comply with the appropriate SCSI and Fibre Channel standards for basic connectivity to their products. Each, however, also implements proprietary value-added utilities and features to differentiate their offerings to the market and these, in turn, pose interoperability problems for customers with heterogeneous storage environments. Disk-to-disk data replication solutions, for example, are vendor-specific: EMC's version only works with EMC; IBM's only with IBM. By virtualizing vendor-specific storage into its vanilla flavor, storage virtualization products can be used to provide data replication across vendor lines. In addition, it becomes possible to replicate data from higher-end storage arrays with much cheaper disk assets such as JBODs (just a bunch of disks), thus addressing both interoperability and economic issues.
The concept of a system level storage virtualization strategy occurs repeatedly in vendor collateral. One of the early articles was Compaq's Enterprise Network Storage Architecture and its description of a storage utility. According to the ENSA document, this technology would transform storage ". . . into a utility service that is accessed reliably and transparently by users, and is professionally managed with tools and technology behind the scenes. This is achieved by incorporating physical disks into a large consolidated pool, and then virtualizing application disks from the pool."
The operative words here are reliably and transparently. Technical remedies, like doctors, must first do no harm. Reliability implies that storage data is highly accessible, protected, and at expected performance of delivery. Transparency implies that the complexity of storage systems has been successfully masked from view and that tedious administrative tasks have been automated on the back end. The abstraction layer of storage virtualization therefore bears the heavy burden of preserving the performance and data integrity requirements of physical storage while reducing the intricate associations between physical systems to a simple utility outlet into which applications can be plugged. Part of the challenge is to get the abstraction apparition conjured into place; a greater challenge is to ensure that the mirage does not dissolve when unexpected events or failures occur in the physical world. Utilities, after all, are expected to provide continuous service regardless of demand. You shouldn't have to phone the power company every time you wish to turn on a light.
The notion of utility applied to storage and compute resources conveys not only reliability and transparency, but also ubiquity. The simpler a technology becomes, the more widely it may be deployed. Storage networking is still an esoteric technology and requires expertise to design, implement and support. The substantial research, standards requirement definition, product development, testing, certification, and interoperability required to create operational SANs was in effect funded by large enterprise customers who had the most pressing need and budget to support new and complex storage solutions. Once a storage networking industry was established, however, shared storage expanded beyond the top tier enterprises into mainstream businesses. Leveraging storage virtualization to create a storage utility model will accelerate the market penetration of SANs and, in combination with other technologies such as iSCSI, spread shared storage solutions to small and medium businesses as well.
Currently, all major storage providers have some sort of storage virtualization strategy in place, with varying degrees of implementation in products. Upon acquiring Compaq, Hewlett-Packard (HP) inherited the ENSA (and ENSA-2) storage utility white paper and has supplemented it with its Storage Grid and other initiatives. IBM has TotalStorage with SAN Volume Controller. EMC's Information Lifecycle Management (ILM) extends storage virtualization's reach throughout the creation and eventual demise of data. Hitachi Data Systems supports array-based storage virtualization on its 9000 series systems. Even Sun Microsystems has a component for pooling of storage resources within its N1 system virtualization architecture. These vendor-driven storage virtualization initiatives reflect both proactive and reactive responses to the customers' desire for simplified storage management and are being executed through both in-house development and acquisition of innovative startups.
In addition, multilateral partnerships are being forged between vendors of virtualization software, storage providers, SAN switch manufacturers, and even nonstorage vendors such as Microsoft to bring new storage virtualization solutions to market. Despite the high confusion factor (and often contributing to it), storage virtualization development has considerable momentum and continues to spawn a diversity of product offerings. This is typical of an evolutionary process, with initial variation of attributes, cross-pollination, inheritance of successful features, and ultimately a natural selection for the most viable within specific environments. Because storage virtualization is still evolving, it is premature to say which method will ultimately prevail. It is likely that storage virtualization will continue to adapt to a diversity of customer environments and appear in a number of different forms in the storage ecosystem.
