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Volume 3, Number 38 -- October 16, 2007

IBM Touts the Power Efficiency of Mainframe Linux

Published: October 16, 2007

by Timothy Prickett Morgan

When IBM caught the Linux bug back in December 1999, the company was just hoping to keep its four server lines relevant by supporting an up-and-coming and possibly quite popular data center operating system on its gear. As it turns out, Linux has been something of a lifesaver for Big Blue's mainframe line, allowing its largest customers to consolidate some Unix and Windows back onto the mainframe, where CIOs can build their empires while saving the company money.

The Integrated Facility for Linux virtualization hypervisor, which is really just a funky version of IBM's VM operating system, is very good at hosting hundreds or thousands of instances of Linux on a single machine; exactly how many Linux instances depends on the size of the mainframe, its main memory and processing capacity, and what those Linux instances are doing. While initially positioned as a consolidation play, the Linux on the mainframe is now being used as a crowbar to peddle mainframes because of the power efficiency the mainframe affords compared to racks and racks of RISC/Unix or X64/Linux servers.

Last week, as part of IBM's Big Green energy efficiency initiative announced earlier this year, IBM is launching a power metering program for its System z9 mainframe line and, based on results of real customers running real workloads, is publishing estimated power ratings for its mainframes. This is akin to the Energy Star ratings for PCs and various electronics, but done in real time on real workloads. The mainframe gas gauge program--that's IBM's name for this new tool, drawing an analogy to miles per gallon ratings for cars--makes use of internal power measurement sensors already inside the mainframe and then displays power consumption statistics on the System Activity Display, and this data can be correlated (presumably by hand) to actual workload statistics to get a sense of unit of work per kilowatt-hour of juice consumed. IBM is offering another program called the Power Estimator Tool to help system administrators look at how much energy will be required as they change workloads to both run the software and to cool the mainframe.

IBM has been gathering information from 1,000 mainframe sites running various workloads using these tools since August 2, when the Environmental Protection Agency in the United States issued a report that outlined how data centers should and could start conserving power. IBM says that the typical mainframe runs at about 60 percent of its rated power in kilowatts while supporting a very large percentage of maximum processing capacity (it is not unusual for a mainframe to be running at 80 percent or higher capacity). IBM also says that based on its analysis of customer data, a typical Linux instance on a mainframe using the IFL hypervisor consumes under 20 watts of juice.

"The mainframe's high utilization rates and extreme virtualization capability may help make it a more energy-efficient choice for large enterprises," explained David Anderson, an IBM green consultant. "A single mainframe running Linux may be able to perform the same amount of work as approximately 250 X86 processors while using as little as 2 to 10 percent of the amount of energy. Customers can now measure the energy advantages of IBM System z."

Of course, there are two problems with this comparison. First, Linux can and will be virtualized, and it is really only fair to compare virtualized Linux on an X64 architecture to virtualized Linux on the IFL on a mainframe. And second, such a comparison does not take into account the cost differential of mainframe hardware and software, even after the deep discounting IBM gives for Linux engines on mainframes. (Linux on the mainframe costs roughly 10 times as much as it does on X64 servers, and mainframe engines cost roughly $100,000 a pop compared to around $3,000 for a new X64 server with four cores.) It would be interesting to see a full accounting of real workloads, virtualized, running side by side on System z mainframes and clusters of X64 servers, with three year's worth of maintenance and support thrown in.


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