Tesco's current assessment of whether to migrate applications onto the mainframe to simplify IT operations and reduce its carbon footprint has sparked debate as to whether the move may signal a possible resurgence of the technology.
The review by the UK's largest retailer was instigated in response to a series of 'green' pledges made by chairman Terry Leahy at the start of the year. One of those pledges was a promise to halve the company's 4.1 million tonne carbon footprint, about four percent of it generated by IT, by 2020.
While doing the evaluation, Tesco discovered that Wintel platforms accounted for 29 percent of this IT carbon footprint, compared with three percent for mainframes and 18 percent for storage systems. As a result, the firm decided to step up its consolidation and virtualisation efforts in the x86-based server domain as an interim step, although it plans to make a decision about more permanent re-platforming by the end of 2009. The goal is to deploy virtualisation as standard in its Wintel server estate and to cut the number of such servers from about 1,500 to between 150 and 300.
So what makes the mainframe environmentally appealing and more 'green' than the Wintel or Unix alternatives? John Phelps, a research vice president at Gartner, says that despite much talk about corporate social responsibility goals, the bottom line counts for more than the environment.
Keeping costs down
Energy bills and lack of datacentre space are both areas that can be helped by efficiency. "One way of reducing energy costs is to ensure that equipment is more efficient and to introduce things like modern uninterruptible power supply systems," says Phelps. "Another is to reduce the load for power and cooling by utilising servers more fully, as a server uses almost the same energy whether it's running at 20 percent or 100 percent capacity."
Un-virtualised x86 servers in siloes typically utilise between eight and 13 percent of their resources at any given time. Unix systems manage between 25 and 30 percent; mainframes as high as 80 to 90 percent.
According to Doug Neilson, a systems consultant at IBM's systems and technology group, the average high-end Z10 mainframe consumes about 15Kw of energy, while a large Intel server consumes about 1Kw. He claims that introducing a mainframe can result in consolidation ratios of up to 30 (unvirtualised) x86 software licences to one (mainframe licence) as well as savings of up to 85 percent in power and cooling costs and the same in floor space because more transactions are undertaken per watt.
But Roy Illsley, a senior research analyst at the Butler Group, points out the lack of reliable, independent figures available in this area. "The issue is whose figures can you believe? The trouble with the whole 'green' debate is that there are no standards you can apply and there are very conflicting views depending on whom you talk to," he says. "It's very difficult to make a judgement because you need independent comparisons based on workload and how you're using it and to work out things like energy savings and carbon footprint from that."
Another area to consider is the energy used in the manufacture of systems, both in the wider supply chain and in disposal. "It's an area that isn't really considered today, but it should be. Mainframes may take more energy to make but they last a long time, while distributed systems may take less but probably only have a three-year lifespan," says Illsley.
Nonetheless, Phelps believes the mainframe provides a "very good" environmental footprint when used as a consolidation tool. "The gold standard for utilisation is the mainframe. Because it runs diverse workloads on one system, you can drive utilisation rates up and you need fewer servers to do it so power and cooling demands are reduced. The latest z10 machines also include up to 64 engines and, because there's not much difference between running one or 12, you can increase the number quite dramatically with little environmental impact", he says.
And this ability to handle mixed workloads is an important one. One of the reasons x86 server farms are often uneconomical...
