The reality of Windows storage virtualization

What you want and what is really out there can be vastly different. First lesson: Be specific about what you expect to get from a vendor.

While Microsoft has several virtualization features in Windows Server 2003, notably MPIO (multi-path I/O), VSS

(Volume Shadow Copy Services) and Microsoft's Distributed File System, they don't translate into a complete virtualization solution. Likewise, a number of Windows vendors, such as DataCore Software Corp., offer products that provide some level of virtualization for Windows systems -- but, again, they're not complete.

It's no surprise that virtualization continues to intrigue IT managers and admins. Who doesn't want a way to optimize and simplify their IT infrastructure? If a virtual machine can make a single system appear and work like multiple systems and make the most of the under-used Windows server environment, bring it on.

Storage virtualization promised a seamless presentation, management and provision of all the enterprise storage (regardless of vendor) with the messy details hidden under the neat virtualization layer. Users could find anything they needed without worrying about where it was stored or what operating system it was stored under. Storage administrators could manage everything from one location and concentrate on the virtual storage entities without worrying about translating the results down to the physical layer. And disaster recovery would be a snap.

Of course, no vendor is currently able to deliver that level of virtualization, and it doesn't appear as though it will be available for some time to come. Interoperability issues, a lack of standards and technical challenges are among the obstacles vendors need to overcome. Most of the virtualization action currently centers on high-end products from big vendors like IBM, Hitachi Data Systems and EMC Corp.

Virtualization is also a place where size matters. Today, the larger the enterprise, the more closely you can approach the ideal of virtual storage. Although they all support Windows, the virtualization products capturing attention, such as IBM's TotalStorage products, Hitachi's TagmaStore and EMC's yet-to-be-released Storage Router, are designed for high-end systems and have the high price tags to match. Some of them, such as IBM's, will work in midrange organizations, but when you start looking at small or medium companies, broad solutions are thin on the ground.

"The issue with Windows is primarily focus," says Simon Robinson, an analyst with The 451 Group, a consulting firm based in New York City. "I don't think these guys [the major vendors] are focusing on Windows primarily."

What does 'storage virtualization' mean?
Today most vendors who are still talking about storage virtualization are using a much more modest definition. When they talk about it, they really mean features and products that hide some of the complexity of provisioning and managing storage behind a layer of virtual entities. This has the advantage of realism, but by this definition a RAID controller or volume management software can be considered storage virtualization products. That's not what comes to mind when most Windows storage administrators think about virtualization.

So, the first lesson is to be very clear about what you're expecting to get when considering storage virtualization.

The real advantages of storage virtualization are better capacity utilization and much easier management. There is enough virtualization available today to be a major help in both those areas.

Capacity utilization is a particularly sore spot with Windows administrators because the amount of wasted storage space tends to increase as the size of the systems being managed drops. One widely cited statistic is that as little as 25% of a Windows system's available disk capacity is actually used to store data, and most of the studies cite 66% or less as the maximum. A virtualization solution that reaches beyond controlling a single disk array can increase utilization.

Some products offer a few sophisticated options. For example, DataCore's SANmelody software features "virtual capacity," which allows storage administrators to assign far more disk space than is actually available. SANmelody monitors actual disk use and automatically provides additional real capacity to the virtual disks as needed. Since the capacity can be anywhere in the storage pool, DataCore says the result is very efficient disk utilization.

Robinson points out that in the real world, storage virtualization is still an emerging technology. "But," he adds, "it's going to be an increasingly viable technology."

Robinson's advice to Windows storage administrators: "It's something they need to be thinking about when building out their storage infrastructures."


Rick Cook has been writing about mass storage since the days when the term meant an 80K floppy disk. The computers he learned on used ferrite cores and magnetic drums. For the last 20 years he has been a freelance writer specializing in storage and other computer issues.
This was first published in April 2005

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