Faster i5 595 Rumored to Be Imminent

Published: February 12, 2007

by Timothy Prickett Morgan

The word on the street is that within the next month or so, IBM will roll out a faster high-end System i5 box, one that matches the basic feeds and speeds of the most powerful System p5 servers that Big Blue sells. It is not clear if this supposed upgrade to the System i5 595 machine will be done as a formal launch or as a special request box that only the largest i5/OS shops are even aware of.

The latter kind of machine is available as an RPQ, which is short for "request for price quotation" in IBMspeak. Historically, IBM often makes machines with special characteristics available on a special bid basis, perhaps using faster processors, or allowing more main memory or a larger number of disk drives to attach to the system.

The reason IBM does this, of course, is because it is well aware of the problem of customers hitting the performance ceiling, which happened with the original System/38s back in the early 1980s, the latter System/36s in the late 1980s, and the original B Series AS/400s back in 1988 and 1989. Through the early years of the AS/400 line, as IBM moved to two-way, then three-way, then four-way servers in the early CISC processor days, customers kept hitting the performance ceiling. With the advent of very powerful PowerPC AS RISC processors in late 1995, performance became less of an issue for all but the largest AS/400 shops, and as the years went by and IBM moved from systems with four then 12 then 24 and then 32 processors, each jump is SMP scalability and the roughly doubling of performance in the processors underneath them meant that a smaller and smaller subset of the OS/400 community needed to have one of these mammoth machines.

But, still, there are probably several hundred very large i5/OS shops that have multiple i5 595 machines--it could even be in the thousands for all we know. IBM doesn't talk about it much. And because these customers write the biggest checks in the System i5 space--and they also generate the biggest software and services sales from IBM's partners--IBM doesn't like to have these customers pushing up against the performance ceiling. It makes them jumpy, particularly when transaction loads keep growing and batch windows keep shrinking.

Which is why it is reasonable to assume that IBM will put out an i5 595 machine that uses either the 2.1 GHz or 2.3 GHz Power5+ multichip modules (MCMs) that are currently in the p5 595 over on the AIX side of the Systems and Technology Group.

IBM launched the Power5+ versions of the p5 595 back in July 2006, finishing off a nine-month revamping of the p5 line with the dual-core Power5+ processors. Last summer, before these Power5+ chips came to market in the p5 590 (expandable to 16 sockets) and p5 595 (expandable to 32 sockets), the 1.65 GHz and 1.9 GHz Power5 chips were what customers had. While these processors were fine at besting dual-core UltraSparc-IV and single-core "Madison" Itanium 2 processors, from Sun Microsystems and Intel respectively, the performance gap on many workloads (excepting the TPC-C transaction processing benchmark test, where IBM still rules) closed as Sun and Intel upgraded their chips last year. Sun's dual-core "Panther" UltraSparc-IV+ processors pulled even with the Power5 and Power5+ chips on a number of benchmarks, and Intel's "Montecito" dual-core Itanium 9000 chips have either met or bested the Power5+ chips--even the fastest ones IBM has in the p5 machines--on a number of tests. If the System p5 is feeling a lot of competitive pressure in the market right now as AIX customers await the Power6 chips--due some time this year--then the System i5 line--particularly top-end customers--feel at least some pressure to consider alternatives.

The i5 and p5 servers, like most servers designed today, were made to support at least two generations of processors. They have enough crossbar bandwidth, memory bandwidth, and I/O bandwidth so that adding faster processors to the machines actually yields the increase in performance that extra clock cycles engender. While IBM was aiming to have Power5+ chips hit 3 GHz or higher, for one reason or another the company has only been able to push the clocks to a top speed of 2.3 GHz. IBM never talks about what happened, but it seems likely that yields are lower than expected on these MCM parts at high clock speeds.

Exactly what IBM will do is unclear. The p5 595 is using the 2.1 GHz and 2.3 GHz parts, but one rumor I have heard suggests that the p5 595 will get a 2.2 GHz clock speed--one that matches the highest clock speed of the dual-core module (DCM) that is used in the i5 570 server. The i5 570 is a two-socket server that can be expanded by adding up to four different servers and lashing them together with NUMA electronics and software to create a 16-socket box with a shared main memory and coherent cache memories. I don't know if the MCM can even run at 2.2 GHz because of other timing issues in the system--relating to DDR2 main memory or I/O buses.

But you can bet that if IBM is not going to ship a System i variant of the Power6 server until 2008, as some people have suggested may happen, then it is going to have to goose the performance on the current p5 595, which is using older 1.65 GHz and 1.9 GHz Power5 processors. (The System p line is expected to get the Power6 chip some time this year.)

Exactly how much performance this upgraded i5 595 box will deliver depends in large part on the clock speed of the chip IBM might put into this machine, how much main memory it has, and whatever tweaks i5/OS V5R4 gets. Just on raw clock speed alone, you would expect a 64-core i5 595 using 2.1 GHz Power5+ processors to have an i5 performance rating of around 203,500 CPWs, with a 2.2 GHz machine rated at 213,000 CPWs and a 2.3 GHz machine rated at 222,750 CPWs. Those bumped equate to performance increases of 11 percent, 16 percent, and 23 percent over the 184,000 CPWs that the i5 595 is rated at using the 1.9 GHz processors.

It would not be at all surprising to see IBM move to denser DDR2 main memory, which is now becoming more affordable, and thereby allowing the number of memory cards in the box to be cut in two. The i5 595, which was launched in October 2004 with 1 GB memory DIMMs, topped out at 1 TB of maximum main memory, and when IBM shifted to 2 GB DIMMs in the spring of 2005, it doubled to 2 TB. This is a huge amount of main memory, but IBM could move to 4 GB DIMMs and thereby allow up to 4 TB of main memory, or it could simply allow customers to go to 2 TB with half as many memory cards. IBM could, of course, do both.

As far as I know, IBM does not offer an RPQ upgrade option for the i5 595 to support the faster Power5+ chips or larger main memories. If you know otherwise, please let me know.

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