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April 12, 2011

IBM Revs Power7 Server Lineup

Michael Feldman

Watson’s decisive win over two of Jeopardy’s top champions on national television earlier this year could turn out to be the most effective infomercial in the history of IT. Capitalizing on that accomplishment, IBM is working hard to highlight the supercomputing technology at every opportunity, including this week’s rollout of new and improved Power7-based servers.

The Power7, of course, was the server chip behind Watson’s game-winning performance in February, and will be the CPU that powers NCSA’s 10-petaflop Blue Waters supercomputer later this year. Although IBM employs Intel Xeon and AMD Opteron processors for its X series servers, the company seems to reserve its greatest enthusiasm for its home-grown Power7 and its associated Power-based rackmount boxes and blades. The latest offerings announced this week include an expanded Power7 blade lineup and speedier CPUs for its Power 750 and 755 servers.

Both the 750 and the 755 are four-socket Power7 servers that were introduced last year. The 750 is built for database serving and general enterprise consolidation/virtualization, while the InfiniBand-equipped 755 is aimed specifically at HPC users. The additional options on the 750 include new four-core and six-core Power7 CPUs running at 3.7 GHz, and two new eight-core Power7s running at 3.2 GHz and 3.6 GHz, respectively. The Power 755, which used to come only with 3.3 GHz chips, is now being outfitted with 3.6 GHz Power7s.

Why they didn’t offer an option for the faster 3.7 GHz Power7s on the Power 755 is a little mysterious. It seems like there would be some interest by HPC users that needed faster threads and a higher memory-to-compute ratio on certain applications.

In the case of the new Power7 blades — the PS703 and PS704 — IBM has actually opted for slower processors. The PS703 is a two-socket (16-core) single-wide blade that substitutes 2.4 GHz Power7 CPUs for the corresponding 3.0 GHz parts in the existing two-socket 16-core PS702. The difference is that the PS702 is a double-wide blade, so presumably the single-wide PS703 could only accommodate the slower, cooler chips in its denser form factor. The PS704 essentially doubles up on the PS703 offering four eight-core Power7 processors, again at 2.4 GHz, in a double-wide blade.

Apparently, the rationale is to offer denser and more scaled-out blades, even at the expense of single-thread performance. According to IBM, the PS704 delivers 60 percent more performance with twice the number of cores, but uses the same amount of space and energy as the older PS702. Cost of the new blades was not specified, but since the Power7 chips are not cheap (even lesser-clocked parts), customers will undoubtedly pay for the privilege of doubling up on their core count.

According to the IBM press release, the University of Massachusetts-Dartmouth is using two Power7 blades (type unspecified) to study the effect of gravitational waves on black holes. According to Gaurav Khanna, professor of physics at UMass-Dartmouth, calculations based on Einstein’s theory of relativity that used to take a month on an 2.5 GHz Xeon-based system can now be executed in less than a week. On this particular application, the Dartmouth team realized an eight-fold performance boost with the Power7 hardware.

It’s not all about Power7 though. In the same announcement this week, IBM also unveiled upgrades to its x86 server lineup, including a new InfiniBand solution for its Intelligent Cluster system (with a built-in Ethernet gateway for high frequency trading work), a 10GbE solution for HPC using BLADE Network Technologies’ RackSwitch, and new platforms refreshed with the latest Intel Xeon E7 (Westmere EX) processors.

IBM’s embrace of Xeons, and E7 in particular, is worth noting. Intel is increasingly positioning its multi-socket Xeons as cost-effective alternatives for the traditionally RISC-based “mission-critical” application space. That pits the Xeon E7 CPUs against Oracle’s Sparc processor and IBM’s Power7, as well as, ironically, Intel’s own Itanium chip.

Intel claimed that an E7 4800-based server matched integer throughput performance of a Power 750 server at about one fifth the cost. Given the Westmere architecture can execute only four floating point (FP) operations per clock cycle to the Power7’s eight, Intel was careful not to claim that its latest Xeons were better than Power7 at FP throughput. On top of that, the IBM chip delivers about four times the memory bandwidth as the latest offerings from Intel. For raw computational horsepower, the Power CPUs still outrun the Xeons.

Where Intel has managed to establish some headway is memory capacity. The E7-4800 CPUs will support up to 2 TB of DRAM in a four-socket setup, while the Power 750 and 755 top out at 512 GB and 256 GB, respectively. That’s a significant edge, especially for analytics workloads that rely on terabyte-sized in-memory datasets.

Ironically, IBM’s super-sized memory solution for big data analytics is provided by its Xeon-based eX5 servers (x3850 X5 and x3950 X5), which were introduced in March 2010. The technology uses a special memory expansion unit, known as the MAX5, which connects the extra RAM to the Xeon servers via QPI cables. The MAX5 adds an extra 32 DIMMs to the 64 DIMMs in the four-socket server, which means a system topped out with 16 GB DIMMs could access 1.5 TB of global memory. Since these boxes now support the new E7 Xeons, and with them, 32 GB DIMMs, maximum memory has doubled to 3 TB per server — the same as in IBM’s Z series mainframe.

For the time being, IBM seems content to let its x86 servers carry the big memory banner. At some point, the company may ramp up capacities on the Power servers, as long as it can justify the application demand from its customers. In the meantime, neither Intel nor IBM is likely to get too vocal about the other architecture’s shortcomings.

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