Out-of-Band Virtualization

Out-of- Band Virtualization

DataCore and other in-band virtualization appliance providers, such as StorageTek, have been fighting a two-front war for the past several years to offset the concerns raised by the placement of devices in the data path between initiators and targets in a switched fabric. On the one hand, such a strategy arguably usurps the functionality of array controllers themselves , mitigating in the process the value proposition that has supported the pricing of high-end arrays to more than 20 times that of simpler arrays. Brand name array manufacturers have been less than receptive to the notion of a "super-controller" place in front of their products that potentially reduces them to a JBOD.

In-band vendors have also fought with peer start-ups comprising an out-of-band virtualization camp, companies like StoreAge and pre-merger Compaq Computer Corporation. Compaq originally conceived of an out-of-band virtualization engine, which it branded as VersaStor, to fulfill the storage management and control functionality requirements described in its Enterprise Network Storage Architecture (ENSA) Whitepaper, considered to be a foundational document describing contemporary SAN architecture.

In effect, the VersaStor server sat on the sidelines of the SAN, evaluating application requirements and capacity utilization, and monitoring available storage resources connected to the SAN infrastructure. The VersaStor server was to accomplish the virtualization of the storage in the SAN by writing virtual volume descriptions to a proprietary chip on the host bus adapter installed in the application server.

The industry turned a cold shoulder to Compaq's proposal of a proprietary VersaStor chip, despite arguments from the vendor that writing the virtual volume descriptions to a proprietary chip would make them less vulnerable to hackers. An alternative that circumvented the proprietary chip issue by writing volume descriptions to application host systems was proposed by StoreAge and is now a fixture of the virtualization solution from that company. ^[5]

The out-of-band approach appeared to be leading the charge as the least intrusive strategy for open systems storage virtualization, but the outlook has dimmed since 2002 as a result of the 1) general economic downturn, which is stalling implementation plans for SANs generally , 2) the disillusionment over SAN management in many quarters , 3) the acquisition of its most well-known champion, Compaq, by Hewlett Packard Company and subsequent "reconsideration" of ENSA by that company, and 4) the recent and increasingly noisy dialogue between leading vendors of both host software-based virtualization products and high-end disk arrays, and switch vendors such as Cisco Systems, Andiamo Systems, and Brocade Communications Systems. As of this writing, virtually all eyes are on switch- makers as the future providers of virtualization services in a SAN.