To virtualize or not to virtualize -- that is no longer the question when it comes to deploying Linux in the data centre. Today, the question is which virtualization approach to take.

One option is to junk dozens, or hundreds, of stand-alone server boxes and consolidate virtualized Linux server images onto a few large hosts. Another is to buy hundreds of new Linux machines and tie them together as a single, virtual system via clustering or grid technology.

"Linux is the strongest example of an operating system that runs on almost any hardware you can think of, and almost any deployment scenario you can think of," says Jean Bozman, research vice president with IDC's Enterprise Server Group. "The style of a virtualized Linux deployment you use depends who you are and what problems you're trying to solve. Clusters, grids, virtualized servers are all possible from the basic building blocks of Linux."

Scale up with consolidation

The trendy data-centre virtualization scheme among Linux users is server consolidation, which aims to address a problem that has roots in the economic downturn of 2001 to 2003, when cash-strapped enterprises started favouring smaller servers over larger ones, Bozman says.

"Over that time, there was a proliferation of volume servers, the likes of which has never been seen," he says. Before 2001, Linux server shipments were around 3 million to 4 million units per year. Now they top 7 million. For customers who built out data centres using hundreds of machines, there is now a push to pare down the amount of "pizza box" hardware.

"Customers who run a data center with 50 or 100 physical servers may need 500 or 1,000 of those machines someday," says Kevin Lehay, director of virtualization at IBM. "How do you manage all of that environment? That's where the scale-up environment takes advantage of that."

The drivers behind the scale-up model include the ability to manage and provision servers more easily, with virtualized servers all running inside one box. Cost savings on power consumption of one large machine, vs. hundreds of single-rack-unit boxes, can be significant. A recent study by Gartner found that the cost of energy in data centres is in some cases almost equal to the cost of the server hardware itself.

For Nationwide Insurance, consolidation of 416 Linux servers onto a single Big Iron box means less walking around and pushing buttons. This is not insignificant when considering wide-scale server maintenance, such as applying Linux kernel or application software patches, according to Steve Womer, senior IT architect at Nationwide Insurance.

"Let's say it takes you 45 minutes per server to apply patches and software fixes, to reboot them and get them back up," Womer says. "Forty five minutes, with 418 servers - that's 315 man-hours. I've got eight people to do all this. That's a long time."

Womer uses a single shared-root file system, which the 418 servers share, running on top of the IBM z/VM virtualization layer of the mainframe. "If you only have one root, it's only two man-hours to patch the copy of the shared read-only root, then you start rolling it through."