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Honestly, do you really know what storage virtualization is?

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"For many years, with our Symmetrix and Clariion products, we've always thought that the basic ability to take all of the physical storage, carve it up into logical units [LUNs] and freely assign it to attached hosts, should reside in the storage array," Hollis says.

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Types of Virtualization
HOST-BASED VIRTUALIZATION Veritas' Volume Manager gives users the ability to virtualize multiple storage arrays.

STORAGE ARRAY APPROACH EMC's AutoIS automates storage management in a heterogeneous environment. Hitachi, Compaq, IBM, Sun Microsystems, Xiotech, and HP also are proponents for placing virtualization software in the storage array.

THE IN-BAND (SYMMETRIC) APPROACH DataCore's SANsymphony 5.0 supplies virtualization to heterogeneous hosts and, at the same time, permits users to virtualize any storage array within its SAN. HP's SANlink was the first virtualization solution to be implemented on an appliance (in-band). The SANlink appliance (an Intel-based PC) resides in the data path between the server and storage devices. FalconStor offers a software version of an in-band appliance that works on both IP SANs and Fibre Channel SANs.

OUT-OF-BAND (ASYMMETRIC) APPROACH StoreAge offers Storage Virtualization Manager (SVM), the only out-of-band (asymmetric) appliance that is connected to the SAN fabric. The SVM provides the mapping function for virtualization, working with an intelligent agent that resides in the host server.

Although it is not shipping yet, Compaq also has a highly innovative implementation of storage virtualization called the VersaStor Executor. VersaStor uses intelligent agent technology to virtualize storage and policy management to simplify administration and guarantee Quality of Service (QoS).

THE STORAGE ROUTER Vicom uses a router as the hardware platform rather than a PC or server. Vicom claims that its Storage Virtualization Engine (SVE) gives users greater scalability, and better performance than engines implemented on a PCs or server-based appliances.

He's also quick to add that his company is not focusing on virtualization as an end in itself, but rather is turning its attention to a larger and more important problem: the automation of storage management in a heterogeneous environment through the use of a policy engine with its most recent initiative - Automated Information Storage (AutoIS).

Although virtualization concepts play a role in this effort, it's an enabler - not a major component of the initiative. WideSky, a new middleware layer, is a key part of the AutoIS initiative.

WideSky, which EMC will make available to partners and competitors that agree to participate in the program, will translate commands issued by applications written to it. Specifically, the WideSky program requires a mutual exchange of APIs between EMC and participating vendors. WideSky has been favorably received by several industry analysts and consultants because they see it as a serious commitment by EMC to open storage management. Michael Hogan, general manager of Imation's professional services organization, an independent storage consultancy, sees this move as a radical departure from what EMC has done in the past. "EMC always talks about being a software company, but this is as close as we've seen the company come to acting like one."

Other vendors that are proponents placing virtualization software in the storage array include Hitachi, Compaq, IBM, Sun Microsystems, Xiotech, and Hewlett-Packard.

The in-band (symmetric) approach
Ft. Lauderdale, FL-based DataCore Software offers virtualization software that can be used on an in-band appliance. It differs from Veritas in its architecture - DataCore uses a storage domain server, which the company defines as "a commercial server platform [Windows NT running on an Intel platform] dedicated to the virtualization and allocation of storage to the hosts."

DataCore's SANsymphony 5.0 supplies virtualization to heterogeneous hosts and simultaneously permits users to virtualize any storage array within its SAN. DataCore claims that its GUI provides ease-of-use that differentiates SANsymphony 5.0 from competitive products. For example, the company points out that an administrator can create virtual disks simply with a drag-and-drop motion. DataCore partners with IBM and Fujitsu Softek in the virtualization market.

HP's SANlink was the first virtualization solution to be implemented on an appliance (in-band). The SANlink appliance - an Intel-based PC - resides in the data path between the server and storage devices. SANlink runs SAN OS - an appliance OS - and several applications, including data mirroring and point-in-time copy. Additionally, SANlink provides security through LUN masking/mapping, among different types of arrays. SANlink has the largest market share among the various virtualization appliances, since it was the first such device in the marketplace and began to gain acceptance almost immediately when it was first introduced over two years ago.

FalconStor Software Inc., Melville, NY, offers a software version of an in-band appliance that works on both IP SANs and Fibre Channel SANs. It does an excellent job of pooling, according to Imation.

The out-of-band (asymmetric) approach
Irvine, CA-based StoreAge, offers the only out-of-band (asymmetric) appliance that is shipping today. The heart of the StoreAge solution is the Storage Virtualization Manager (SVM), which runs on an appliance connected to the SAN fabric. The SVM provides the mapping function for virtualization, working with an intelligent agent residing in the host server. Host servers can be Windows NT, Windows 2000, Sun Solaris, Linux, HP-UX, and AIX. The agent retrieves volume metadata from the SVM and permits the server to communicate directly to the storage hardware for read/write operations.

Although it isn't being shipped yet, Palo Alto, CA-based Compaq also has an innovative implementation of storage virtualization called the VersaStor Executor. VersaStor uses intelligent agent technology to virtualize storage. The agent, called a vector, resides in the host. The mapping information permanently resides in the VersaStor Executor. When the virtualization process starts, mapping information is uploaded into the vector, where it's cached. Virtualization commands are sent to the vector in the host from the VersaStor Executor software that resides in the appliance. Then, the vector executes the commands.

This was first published in June 2002

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