Storage /

Virtual benefits

By Mike Karp
Network World Storage Newsletter, 02/20/02

Virtualization adds a layer of abstraction between storage and the applications that access it. In this case, " abstraction " refers to the fact that the various storage media are - as far as the applications are concerned - effectively joined together into a single large entity. Your applications and management software address the contents as if they were physically on this disk and never have to worry about where the data actually is stored.

In simple terms, it is as if the " c: " drive on your PC extended out towards infinity, and that no matter where the data is actually stored (even if it were on a CD-ROM or some external media), you could always access it as if it were on that one disk.

This can deliver lots of value in large, complex IT situations. Not the least of such benefits is that - at least in theory - virtualization provides a very efficient method to centrally manage storage that has spread across a wide variety of platforms.

But what's the downside? The technology is being implemented in a number of ways by a number of vendors, so at this point it's hard to generalize. Questions about extensibility frequently arise - can some implementations scale painlessly to meet your increasing demands for storage space? Another question we raised recently was whether virtualization of essentially homogeneous environments (the " SAN in a box, " for example) could offer the rapid payback that we might expect in more complicated situations?

Because of the media invisibility that all implementations of virtualization provide, all software management apps are one step further removed from the hardware (hardware management applications that directly address the hardware should be unaffected). There is a lot of value in this, but in one sense at least, it may also be something of a two-edged sword.

A tremendous benefit that some software vendors (Tivoli and BMC are good examples, but there are others) are beginning to offer is intensive automation of their products. This means they are able to incorporate into their products a good deal of experience that can be applied to building intelligent policies to drive their apps. For example, a back-up application may be able to take advantage of some built-in components of Oracle, or some knowledge of the hardware on which the application or data is sitting, to increase the efficiency of the operation.

This is sometimes referred to as " application awareness " , but it is becoming much more than simple awareness of an application's capabilities. For wont of an existing term then, I'll call this " application versance. "

There is a potential conflict between virtualized storage and application versance. Because the management application can no longer see the hardware, it loses its opportunity to take advantage of that hardware's specific capabilities. Whether, for example, an app will be able to autoconfigure or autodiscover in a virtualized environment is still very much up in the air.

While no vendor is yet talking very much about this issue, it has of course not gone unnoticed by the vendor community. XIOtech, for example, which incorporates some sophisticated virtualization into its boxes, is reportedly taking a good look at this. So too, presumably, are many others.

None of this should scare you away from examining the option of virtualizing your storage environments. But the interplay between application versance and virtualization should be added to the list of issues you discuss with your vendors.