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Cray XK6 super mates Opterons with Nvidia GPU workhorses

Ceepie-geepies all around

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Gemini dream

The Gemini interconnect is a kind of averaging between the SeasStar2+ interconnect used in the XT5 and XT6 machines and a future interconnect called "Aries" that is being created for the US Defense Advanced Projects agency for a series of machines called "Cascade", due in 2013 or so. El Reg walked you through the guts of the Gemini interconnect last May, when it debuted. Here is what it looks like conceptually in the Cray XE6 x64-based supers and how it differs with the XK6 ceepie-geepies announced today:

Cray XE6 and XK6 schematic

Cray's XE6 and XK6 and their Gemini interconnect (click to enlarge)

Cray announced last September that it planned to add GPU coprocessors to the XE6 line, but was a bit cagey about how it would be done beyond using PCI Express links to hang Nvidia's Tesla 20 series of GPU coprocessors off the Opteron processors in its supers. Cray hinted at the time that it was planning on adopting the future "Kepler" GPU cards within the XE6 frames, but never came out and said that. They did say, however, that the GPU coprocessors would link to the CPUs through PCI Express links.

Cray XE6 Blade Server and Gemini Interconnect

Cray's muscular XE6 blade

The XE6 blade has two Gemini interconnect ASICs on the left (which is the back of the blade), with four two-socket server nodes and their related memory banks to the right of the interconnect.

To make the XK6 blade, Cray took out the four sockets on the right side of the XE6 blade, dropped in four SR5670/SR5100 chipsets from Advanced Micro Devices and four of variants of the new fanless Tesla M2090 GPU coprocessor announced by Nvidia last week. Cray is not using the M2090, but rather a special embedded version of the card called the Tesla X2090, which server makers can buy to put on their own system boards, as Cray has done.

Cray XK6 supercomputer blade server

Cray's Tesla X2090–equipped system board

The AMD chipsets are under the aluminum silver heat sinks on the right side of the blade, and the Tesla X2090 GPUs are under the four copper heat sinks on the right side, to the top and bottom of the chipsets. The chipsets implement the PCI Express 2.0 links between the GPUs and the Opteron processors on the left side of the blade. The GPUs have their own main memory, of course – in this case, 6GB of GDDR5 graphics memory. The Opteron portions of the XE6 and XK6 blades have four DDR3 memory slots running at 1.6GHz for every G34 socket. On the XK6, that works out to 16GB or 32GB per two-socket server node using 2GB or 4GB memory sticks.

Technically, Cray does support 8GB sticks if customers want them, and it could go all the way and support 16GB memory sticks, but these are both too expensive for most HPC customers, says Bolding. On the XE6 blade, each of the four nodes has another Opteron G34 socket linked to it over HyperTransport 3 (HT3) links, and has another four memory slots for double the memory capacity.

The Opteron side of the blade is physically identical to the current XE6 blade, but Cray is not shipping the XK6 with the current 12-core Opteron 6100 processors. Rather, Cray will wait until AMD gets the 16-core "Interlagos" Opterons into the field in the third quarter. AMD's wafer-baking partner, GlobalFoundries, is making the Opteron 6200s, as the Interlagos chips will be called, using its 32-nanometer process. AMD interim CEO Thomas Siefert promised Wall Street last month that these chips, which are based on the new "Bulldozer" cores and which plug into the same G34 sockets as the Opteron 6100s, would ship by late summer.

Cray, having been burned by Opteron delays in the past, is only saying that the XK6 will ship in the second half of 2011.

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