The IT industry continues to trend towards hosting ever more massive workloads with scale-out architectures, in which large numbers of industry-standard servers containing x86/x64 processors are joined into clusters or grids. Much of the attention in recent years has been on scaling out with blade servers, which allow large numbers of servers contained in specialized modules to be deployed and managed in an optimal hardware footprint. Now, IBM has introduced a new server design, called the iDataPlex, which introduces a new level of density for cramming large numbers of processors into a small amount of space, using traditional rack-mounted servers rather than blades.
The iDataPlex concept resulted from a number of conversations IBM executives and engineers had with major web-based businesses and leading-edge financial services organizations. All of the major server vendors, including IBM, were pushing blade servers to these customers. But blades were too expensive for these massive scale-out deployments and traditional rack servers were not sufficiently customizable and lacked the required density. As a result, most of these customers ended up building their own server complexes simply because nothing on the market met their needs.
In designing the iDataPlex, IBM took a "clean sheet" approach that was inspired by blades, but uses the traditional rackmounted form factor. Server vendors like HP are pushing blades everywhere, and other companies like Dell and Sun are pushing a combination of rack and bladed servers. But no one had seriously looked at rack servers in years. IBM chose to use the same 42U standard rack envelope, but turn it sideways and shorten the servers themselves to 15 inches. That allowed up to 42 2U servers or 28 3U servers to be positioned into the same space that held half that many in a traditional rack design. A maximum of 672 processor cores per rack doubles the conventional rack density. Due to cost considerations, the iDataPlex has no backplane and relies on cables to carry all of the I/O. Each iDataPlex is entirely built in China in an IBM facility. Like mainframes, every system is custom built. It takes 3-4 months to sell and IBM expects that 70% of deployments will be in a new or redesigned datacenter.
For cooling, there are no fans attached to the processor boards themselves, only in the 2U/3U chassis, each of which contains 4 large fans. Further, IBM offers an optional rear-door heat exchanger for the iDataPlex that uses water cooling. The rack can be cooled sufficiently without the heat exchanger, which costs $75-100,000. However, when the water cooling is used, the demands on Computer Room Air Conditioning (CRAC) devices can be lowered or even eliminated in many cases. The result is a staggering 40% reduction in datacenter cooling costs today, and IBM is working to push that to 60% in the future.
Both rack servers and blade servers were designed back during the time when performance and performance density were key requirements. Reliability was also paramount and numerous redundancies and failover capabilities were added to ensure that applications would remain available even after a major server or component failure. The problem is all of the added redundancies pushed up the cost. With cloud computing, the old requirements have changed. Component reliability is no longer needed because the application itself can deal with failures. With tens of thousands of servers, failures occur all the time and bad servers can be swapped out on an hourly or daily basis. The cost of computing, and specifically the operating cost, is now the defining criterion. Anything that can save on the cost of electricity is a huge plus. IBM realized that this new market is now large enough to support a specialized server design that prioritizes low energy consumption and density over redundancies. Today, there are few customers demanding this type of solution, but the ones that do exist buy tens of thousands of servers at a time for deployments that can reach 100,000 servers or more. We at IDEAS feel that iDataPlex is a strong solution for this new class of customers.
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