IBM Beefs Up The Power7+ Midrange With Double-Whammy Sockets

February 11, 2013 Timothy Prickett Morgan

While the entry part of the Power Systems market has been awaiting its Power7+ refresh, putting new processors and fatter memory and disk drives into essentially the same enclosures that were refreshed at the end of 2011, the midrange of the Power Systems line has been getting a little long in the tooth and was perhaps more in need of some re-engineering. And luckily for customers using midrange Power iron, that is precisely what IBM has done as part of the February 5 announcements.

Not only is the Power 750+ getting a complete revamp while holding the core count steady, but there is a variant of the box called the Power 760+ that pushes the core count, performance, and memory capacity up even further.

You would have a hard time telling the Power 750+ from the Power 760+ even if you squint very hard. (The Power 750+ is on the upper left and has the green stripe along the right side, while the Power 760+ is on the lower right with the black stripe.) Both are based on a new 5U chassis that sports more and faster I/O, which is possible because the Power 750 chassis at 4U was a bit cramped with four processor cards inside. So by adding a little extra space and cutting out two disks drives (from eight to six), IBM is able to add room for twice as much main memory slots, one more peripheral slot, and multifunction networking cards that give customers a variety of options.

The Power 750+ server, which is known as 8408-E8D in the IBM catalog, has four processor sockets and supports up to 32 Power7+ cores. The processors used are not full-on eight core chips, one per socket, but rather two four-core Power7+ chips with half their cores and caches blocked out (they are half-duds, basically) with two of these crammed into one socket. So why would IBM use two four-core chips rather than just put one eight-core chip in each socket? I will tell you.

If you sort through the Power7+ processor bins, you might find one chip that runs perfectly fine at high voltage, but half the cores or half the cache or both have gunk on them and do not work right. And if you search through these, you might find some that run at lower voltages and produce less heat even though they are running at 3.5 GHz and 4 GHz as they do in the Power 750+ server. So you can now put two of these chips, which you might have otherwise thrown out or only been able to use in a Power 720+ machine into the much more expensive Power 750+ box. These are chips that might have made it into a workstation or a blade server under normal circumstances.

The side effect of this double-whammy socket is that with memory controllers on the die, when you double the chips, you can double the memory controllers and therefore the maximum amount of addressable memory. You may not use that extra memory capability, but it is inherent in the system. In the case of the Power 750+, the doubling up of memory controllers allows the machine to address up to 1 TB of main memory without resorting to 64 GB DDR3 main memory sticks and using (presumably) cheaper 32 GB memory features. The Power 760+ supports the 64 GB sticks and can scale to 2 TB of memory.

The Power 750+ with the 3.5 GHz Power7+ double-stuffers is rated at 52,000 CPWs for IBM i workloads, and a fully loaded box with four processor cards using the 4 GHz Power7+ dual-chip modules (or DCMs as IBM calls them) is rated at 208,000 CPWs across its 32 cores. The machine ditches the old PCI-X and PCI-Express 1.0 slots and has six PCI-Express 2.0 slots. IBM is not supporting PCI-Express 3.0 peripherals, which the Intel Xeon E5 processors do. This is not a huge issue, but it will be if IBM customers have to wait until the Power8 processors in 2014 or so to get PCI-Express 3.0 peripherals. You can’t give Intel that kind of lead.

The Power 750+ machine also sports two GX++ ports hanging off the processor, which is better than the single GX++ port and shared GX port that the Power 550 and Power 750 predecessor machines had. The server can support two 12X I/O loops if you have two, three, or four sockets installed (you don’t get any when there is only one processor card). With two drawers per loop, a Power 750+ server can have as many as 1,302 disk drives attached to it for a maximum capacity of 1.17 TB using 900 GB disks.

The Power 760+ system, which is known by the product number 9109-RMD, is a special box in a number of ways. First, it is double-stuffing the sockets with six-core processors that run at either 3.1 GHz or 3.4 GHz, which gives you up to 48 cores and up to 274,000 CPWs of IBM i oomph. That’s 31.7 percent more performance than the top-end Power 750+ machine in the same chassis with a 15 percent drop in clock speed.

The Power 760+ also requires a Hardware Management Controller (HMC) console. IBM has not explained why, but it probably has to do with the fact that the Power 760+ has capacity-on-demand processor core activations, and something has to control that. The Power 750+ doesn’t have this COD feature. Another difference between the two midrange machines is that you can install a Power 750+ yourself, but IBM has to install the Power 760+ system.

The Power 760+ can support up to twice as much main memory if you can afford the 64 GB memory sticks, and it supports the same 1,302 disks and 1.17 TB maximum capacity as the Power 750+ machine.

The Power 750+ and Power 760+ machines support IBM i 6.1.1 and 7.1, AIX 6.1 and 7.1, Red Hat Enterprise Linux 6.4, and SUSE Linux Enterprise Sever 11 SP2. They will ship on the Ides of March, and for those of you who don’t remember your Julius Caesar, that is March 15. Not always a bad day, unless you are an emperor who can’t see the auguries of doom around you.