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The virtues and vices of virtual appliances

Virtual appliances bundle up just the software functions required for a specific job into a virtual machine that can be deployed on any hardware. So what’s the downside?

Appliances are expanding their presence in today’s data centers. When they first arrived, they took the form of turnkey boxes -- pre-bundled with software -- that VARs plugged into data centers to assume prescribed tasks. 

More recently, there’s been a flood of virtual appliances in which VARs or ISVs use tools like VMware Studio or Novell’s SUSE Studio to parse out just the bits and bytes necessary to perform specific jobs. That software bundle can then run on whatever hardware the customer has available. 

But in spite their benefits, appliances aren’t for everyone. VARs need to be able to counsel customers on when to opt for virtual appliances. And if that decision is made, they need to help customers determine in what scenarios a virtual appliance is a better fit than a physical appliance. 

The question is what, if anything, is the downside to this slick virtual appliance technology? The definitive answer is that it all depends. 

It depends on how virtualized your IT shop already is. It depends on how well the virtualization stack within the virtual appliance fits in with the rest of your company’s stack. It depends on what kind of appliance it is -- and there are appliances for almost any application, including storage, security, systems management, email -- you name it. 

And it depends on what storage array is running at the back end of it all. Big, high-end, high IOPS arrays with fast interconnects may mean less of a performance hit for a virtual appliance. 

Not a virtual cure-all

Here’s the thing: Although virtualization is typically preached as a cure-all for anything that ails enterprise IT, there are tradeoffs to using virtualization versus running stuff on physical machines -- in this case, a physical appliance. Plainly put, virtualization in any form can cause performance issues if it is not done correctly. 

One long-time IT pro, who requested anonymity, goes even further: “It’s not even whether or not you do it right. It’s a plain fact that virtual machines have worse performance [compared to physical machines]. Period. Amen. It’s just that some apps can stand it better, some can’t.” 

Bearing that in mind, virtual appliances make perfect sense when a company has hardware around that is not fully utilized. They also provide a useful bulwark against vendor lock-in. 

At the very least, the notion of software-only virtualized appliances means that IT pros can run them on their hardware of choice, not the vendor’s hardware of choice; said ChrisWolf, research vice president at Gartner Inc. 

Indeed, this approach flies in the face of the traditional “appliance” sell where the software is locked to an often proprietary hardware appliance, specifically built for the application at hand -- or so it is advertised. 

In Wolf’s view, a virtual appliance can be a terrific solution for some business continuity applications. 

“If I need to fail over, I don’t have to move to and from a physical box, I just move the virtual machine,”Wolf said. “That’s a lot of flexibility that can be very attractive.” 

But users must not be fooled by the whole performance issue thing, said John Ross, CTO of GreenPages Technology Solutions, a Kittery, Maine, solution provider. Aside from the underlying physical disk, he said there’s no reason that everything in a data center should not be virtualized. And by that, he means everything. 

Ross said he understands the cultural resistance to that notion. “There are some challenges in security appliances -- where people still look at these things as a gate, and so they don’t like them to be virtual,” he said. 

For a solution provider, the key is to bring to the customer a couple of vetted choices for any given application. “We usually come in with A, B and C offerings -- a choice of two hardware products and one cloud-oriented or virtual appliance option,” Ross said. Then the VAR can sort through the pros and cons of each option with the client, he added. 

Another large reseller in the mid-Atlantic region, who asked not to be named, said it’s important to tread carefully when introducing any new technology into any existing data center so as not to disrupt what’s already there. 

Virtual appliances can be “a huge landmine” in some shops, the reseller said. “You want virtualized appliances in highly virtualized environments. In some of those cases, some tasks cannot be done on physical [machines]. Recommending against using a virtual appliance could be bad.” 

Conversely, if the data center is not highly virtualized, bringing in a virtual appliance that is outside the purview of a data center’s existing management structure could also be a nightmare. “If you have started down the orchestration path, and your physical machines cannot be managed by your virtual tools, that can cause problems,” the reseller added. 

Virtual vs. physical appliances

What it comes down to is a cost-benefit analysis. “Virtual appliances are indeed advantaged in that they run [on whatever hardware you want],” said the CTO of a large financial services firm who asked not to be identified. “Most physical appliances run on a Linux distro these days, but you seldom get optimum performance from a VM,” he said, adding that a lot of these appliances need to be optimized too. “So pick your poison,” the executive said: It’s either cheap, flexible and slow virtual appliances or fixed, fast and more expensive physical appliances. 

Virtual appliances can be a natural fit in environments that are already highly virtualized, said Edward Haletky, CEO of The Virtualization Practice LLC, an analyst firm in Wrentham,Mass. But unless a data center is 100% virtualized, it will need some combination of physical and virtual capabilities, he said. Given that most shops in the United States hover around the 30%virtualization mark -- with the leaders topping out at 80% virtualized -- that means a lot of mixed environments, Haletky said. 

But virtual appliances do suit some use cases over others. In storage, for example, “it all depends on the IOPS and the I/O latency measured inside the storage network,” Haletky said. “For that, a virtual appliance may be perfect for the dev-test environment, but for production you may need full-blown hardware.” 

Virtual storage appliances come in a few flavors. “A storage optimizer aggregates and speeds up access to disparate hardware,” Haletky said. “Some optimize and perform replication, and in that case, you may get better functionality on a virtual appliance compared to your physical hardware,” he said. “As not every storage solution has replication, in those cases you may want to look at a virtual appliance.” 

About the author:
Barbara Darrow is senior news director for TechTarget’s Data Center and Virtualization Media Group and has covered technology, business and the channel formore than 20 years as reporter and editor. Prior to TechTarget, Darrow worked at CRN where she focused on channel issues and software news. She has also written for InfoWorld, ComputerWorld, NetworkWorld, InfoSecMagazine, eWeek and other publications. Contact her at

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