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Study: I/O is Main Hindrance on Virtualization

UPDATED: Xsigo Systems on Monday released a study that it says identifies a major complication in the deployment of virtualization servers: the data bottleneck from all of the I/O that takes place in a virtualized world.

The current I/O  infrastructure in servers was designed for traditional usage, which is typically one application or use per server. If a machine was acting as a Web server, it would connect to a database or e-commerce system, while a mail server would connect to a storage system.

This allowed for servers to run in a 1U "pizza box"-style server with a single gigabit network connection. But in a virtualized system, multiple application servers require multiple connections and multiple Ethernet ports to handle several gigabits of data going in and out of the server.

"Think about this: The race to virtualization is all about density," Greg Schulz, founder and senior analyst with The StorageIO Group told "You can squeeze multiple servers onto a virtual machine, but as you put more and more of those servers, you have to do something about the connectivity."

"If you put the equivalent of eight servers on one machine and each needed one gigabit of bandwidth, that's eight gigabits," he said. "A one-gigabit Ethernet port isn't enough."

Xsigo Systems is a startup, launched in September specifically to address the I/O connection bottlenecks. Not surprisingly, its report suggests there's indeed a need for its products. Its flagship offering, the 780 I/O Director, provides a single interface into a 1U server for all virtualized connections.

Using one or two InfiniBand connections instead of multiple Ethernet connections, the Director can reduce the amount of cabling required by up to 70 percent, according to Jon Toor, vice president of marketing at Xsigo. At the same time, it can provide a full 10-gigabit bandwidth for all virtual applications. A dual-rate InfiniBand port can hit 20 gigabits.

To accommodate virtualization I/O, servers require six to 10 ports, which means a 4U box to handle all those cards and ports. The Xsigo survey found that 75 percent of virtualized servers have seven or more I/O connections per server, compared to two to four connections for a server running without virtualization software.

So while virtualization may allow a datacenter to consolidate from 500 servers to 100 servers, you end up with a spider web of cabling. "What ends up happening is you end up connecting everything to everything," Toor told "People can overrun traditional I/O with services they have in a virtualized environment, unless you put a lot of the load in the same physical box."

Managing the physical cabling is as important as managing the I/O and the adapters, Schulz said. "For users looking to save money, it's about an ease of management and reducing the amount of adapter cards and cabling," he said.

In a standard virtual server, each port runs at 1 gigabit and the ports are separated. With the Director, the full 10 gigabits are available to any application that needs it. So if one application requires several gigabits and the others don't require it, that app can have full access to all of the bandwidth.

Adding to the problem is the fact that ports are often being assigned to applications by MAC address, so it's difficult and time-consuming to move an application to a new physical server because the networking has to be reconfigured on top of moving the application.

Xsigo found that 35 percent of virtualization users had to reconfigure I/O connections six or more times in the past year, usually when they moved a virtual server to new physical hardware.

The survey also found that 58 percent of virtualization users had to add connectivity to a server specifically for virtualization requirements, and because of this, had to use larger hardware -- 4U instead of 1U -- which consumes more power.

Privately-held Xsigo features some heavyweight venture backing from the likes of Kleiner Perkins, Khosla Ventures and Greylock Partners.

Update adds comments from Schulz.