The virtual server is one of several practices aimed at increasing the efficiency of the data centers and server farms that are the heart and soul of enterprise IT. These practices, which ultimately cut costs and increase efficiency, are getting a big short-term boost from a bad economy that is forcing CIOs to economize. Moreover, executives realize that the initial ways in which data centers were thrown together are not sustainable going forward.
Virtual servers are part of a bigger effort to redesign data centers on the fly, analysts say. During the Internet boom, the accepted approach was to buy a separate server for each application. Space wasn't an issue, and there was a reluctance to deal with the complexities of running different applications on the same server. Mundane topics like heat dissipation versus data center cooling capacity weren't considered -- money was flowing and there was no reason to economize.
Eventually, of course, just about everything in that equation changed, beginning with the last point: the economy tanked. This made partial use of so many servers, and the purchase of a new machines for each new application, unwise. In addition to hardware costs, IT departments wanted to shed, not add, administrative staff. Data center floors became crowded like rush-hour subway trains with boxes -- all running at a fraction of their capacity.
Ideas such as grid and mesh computing, server blades and virtual servers -- techniques that can be used in concert -- are designed to confront these issues. Grid, mesh and related approaches let geographically separate machines work as one entity. By cramming multiple servers into one chassis, blades save precious floor space, reduce pressure on the hosting facility and cut the tangle of cables. Carving existing platforms into virtual servers -- each running its own operating systemincrease the percentage of a server's capacity that can be utilized at any given point in time.
Virtual server schemes are the most granular way of approaching the problem because they reach into the guts of the machines and determine how hardware resources are doled out between multiple operating systems and the applications that run on them. Each tenant OS and its apps are not "aware" of others running on the machine.
There are three approaches to subdividing a machine, says Gordon Haff, a senior analyst with research firm Illuminata:
- Physical partitions, as the name implies, involves electronic separation between pieces of hardware. Separate OSes run on each cordoned off section of hardware.
- Logical partition focus on creation of a software layer that controls the connection between the underlying hardware and the OSes and applications that runs on it. Logical partitions, while more granular than physical partitions, don't enable fluid changes in resource distribution between resident OSes.
- Virtual servers feature a software management layer that enables the resources of the computer to be sliced and diced flexibly.
Virtualization should not be confused with resource management software (RMS). RMS schedules what resources are provided to what applications at a given point in time from a single OS. Thus, a company can delegate the lion's share of server capacity to management of logons from 8 to 10 AM and switch to inventory control from 2 to 5 AM. Theoretically, experts say, RMS and virtual servers can be complementary. In other words, any number of virtual servers running on a given hardware platform can use RMS. "In one camp is one OS running a lot of apps," says Tony Iams, a senior analyst at DH Brown. "In the other is a lot of OSes, each running their own app."
Virtualization is a common attribute of mainframes. There are two theories explaining why it is a more substantial challenge in the Intel world.
One says that Intel architecture in general is too immature to be trusted to run business-critical apps. More specifically, these people say that Intel architecture simply wasn't designed with virtualization in mind. Creating virtual servers on Intel machines, these analysts say, requires methods to reconcile different OS configurations and to keep apps from fighting with each other over resources such as dynamic link library (DLL) entries, disc I/O, CPU capacity, libraries and other elements. This means that designers must finally grapple with the issues they sought to avoid by putting apps on their own servers to begin with.
"[T]o figure out how to multiplex instruction screens from multiple OSes onto a single piece of hardware is extraordinarily difficult because the Intel instruction set is not strictly virtualizable," says Michael Mullany, senior director of product management for VMware.
A second group agrees that the Intel architecture is playing catch up. They maintain that rapid progress is being made. Many of the issues making Intel virtualization difficult, they contend, are more related to how the apps are written than the underlying OS.