Al Gore's recent movie An Inconvenient Truth sounds the alarm on global warming. Being exceptionally high consumers of electricity, data centers contribute to the problem. The U.S. Department of Energy states that data center energy use can be a hundred times higher than a typical commercial building's energy use. According to a June 2006 article in The Wall Street Journal, "One large data center can consume enough juice to power a small city of 30,000 to 40,000 people."
Most organizations do not grasp the disproportionate use of electricity and associated costs of operating their own data centers. I can say that with assurance, because I've asked hundreds of organizations if they knew the overhead cost of powering their data centers, and not one knew the answer. Odds are that a business spends at least as much on powering and cooling the servers in the data center over time as it spends on purchasing the hardware.
The cost of server sprawl
On average, servers have a utilization rate of only 5% to 10% -- and utilization is decreasing as more powerful servers proliferate. Although servers sit idle most of the time, organizations continue to purchase more of them in order to provide an isolated operating environment for each new application. Additional servers are included in the data center for testing and clustering and as disaster recovery centers.
The cost of this server extravagance is substantial. In addition to the purchase price and set-up expense, each server consumes floor space, requires ongoing maintenance and needs to be upgraded as the hardware becomes obsolete. Most important is the daily cost of electricity, which is included in the overhead -- and each server consumes lots of electricity.
The amount of electricity used, of course, depends upon the server. An efficient low-end server might use as little as 200 watts an hour, while a newer, more powerful server can consume 450 watts. Older servers can use well over 500 watts. In order to calculate the cost of running a server, we need to know the cost per kilowatt hour (KWH). Pacific Gas and Electric says that a good average for businesses in northern California is 15 to 17 cents, and rising. Because servers usually run 24 hours a day, seven days per week, that means the total electric cost per month (at 15 cents per KWH) to operate just one low-end server comes to $22; a newer server costs $38 and an inefficient server costs more than $50.
This cost alone should be enough to give a CFO concern, but that's not the end of the story. The actual cost is roughly double that amount due to the electricity required to counteract the heat generated by servers and other data center equipment. As you may know, failure to adequately dissipate server heat results in the reduced lifetime of its parts, increased downtime and, possibly, server failure.
The amount of power it takes to cool a server depends on many variables, including the type of server, the composition of the data center and the architecture of the cooling system. Given this variability, some researchers arrive at a lower power estimate for the overhead of air conditioning -- at a quarter to 40% of the total energy cost. But we can simply assume that it requires an equivalent amount of electricity to cool servers as it does to power the servers.
It doesn't stop there. PDUs, generators and additional circuits are required in order to accommodate the ever-growing number of servers. Further electricity is required by UPS units that moderate the current and provide backup power in the event of power failure. These devices consume up to 20% of the total electricity demand. Using some rounded numbers, total energy costs can be estimated at between $50 and $100 per server per month.
Making a change with virtualization
Virtualization changes the data center dynamic by allowing many virtual servers to share physical hardware. Virtualization software packages -- manufactured by companies such as VMware, XenSource and Microsoft -- enable much more efficient use of x86 servers, meaning multiple operating systems can run on a single physical server.
Each individual operating system, along with its applications, runs in its own virtual machine that looks just like the hardware server for which it was designed. Virtual servers are guaranteed specific amounts of processor cycles, memory access, disk I/O and network bandwidth. The number of virtual machines that can be consolidated onto a physical server depends on the characteristics of the original machine and the server host. A rule of thumb is that a two-CPU dual core server should, on average, adequately accommodate up to 20 virtual machines.
Market leader VMware's product enables automatic movement of a virtual machine to another physical server, should its resource requirements exceed the available physical server resources, without disruption to user sessions. Servers, in effect, become like drives in a disk array. Network administrators no longer need to be concerned about individual physical servers any more than they focus on individual hard drives. When aggregate RAM, CPU or network I/O resources start to become constrained, administrators can simply add another server to the pool. And since virtual machines are hardware agnostic, the brand of server is unimportant.
Another benefit of virtualization is automatic transfer of virtual machines from a failed physical server to other physical servers that have adequate resources. This enables organizations to provide high availability for all of their data center servers simply by providing N+1 capacity as opposed to duplicating every server. Disaster recovery centers also benefit from consolidation; under virtualization, the disaster recovery center requires far fewer physical servers to provide recovery for numerous virtual machines.
Virtualization by the numbers
Even without considering costs, the benefits of virtualization -- such as high availability and improved disaster recovery -- present a compelling story. Fortunately, the economic benefits of virtualization are substantial as well.
Consider, for example, a data center populated with a mix of old and new servers of varying configurations with an estimated average total energy cost per month of $75 each. If the organization consolidates 100 physical servers onto six new two-CPU dual core servers, the net electric/power savings for the 94 virtualized servers comes to approximately $423,000 over five years. If the organization pays $6,000 for each physical server (including tax, shipping and set-up) and commonly refreshes servers once every five years, then additional savings of approximately $560,000 are realized over a five-year period for 94 servers that don't need to be replaced. This is a combined savings over five years of almost $1 million.
There are additional long-term cost reductions with virtualization. New applications will reside on cost-effective virtual servers instead of new physical servers. This results in lower electric/power requirements and a reduction in network cards, network switches, SAN HBAs and maintenance contracts -- not to mention a potential reduction in data center components such as air conditioners, PDUs and UPS devices. Because virtual machines require only about 33% of administrative time as their physical servers, there is a further significant reduction in the IT staff time required to support them.
Meeting global warming responsibilities
The topic of global warming is frequently in the headlines, and scientists believe that increased levels of carbon dioxide contribute to global warming. Whether or not the threat is real, the generation of power -- especially from coal-burning power plants -- contributes to the increased amount of carbon dioxide in the atmosphere. Under international accords, the U.S. must reduce carbon dioxide emissions at the same time estimates indicate that 25 million tons of carbon dioxide will be released each year in order to power data centers. Using virtual technology not only slashes costs and enhances the IT infrastructure but also contributes to an organization's social responsibility by unplugging servers and reducing the demand for electricity.
About the columnist: Steve Kaplan is president of AccessFlow Inc., a Benicia, Calif.-based consulting firm specializing in enterprise virtualization. He is also co-author of the book, Citrix Access Suite 4 for Windows Server 2003: The Official Guide, published Osborne/McGraw-Hill.