Memory: The New Power Hog

Computerworld - For engineers developing the next generation of servers, the CPU is no longer the biggest design obstacle to controlling power and cooling costs, which is a major issue for many data centers. "It used to be that the processor was our main concern," says Roger Schmidt, chief thermal architect and distinguished engineer in IBM's server and workstations division.

Not anymore.

System designers have been given a reprieve from contending with spiking CPU power demands in the volume server market as both AMD and Intel have continued to move to more energy-efficient multicore designs. For now, both chip makers are pledging to hold the line on power consumption while continuing to offer improved performance in smaller packages.

The other big kahuna -- power supply conversion losses -- is gradually coming under control. The power supplies found in most commodity Wintel servers today can waste 35% or more of incoming power before it ever reaches the proc­essor. But Sun, HP and IBM have all developed power supplies that exceed 80% efficiency, even at low load levels. Some servers are now shipping with power supplies that exceed 90% efficiency.

The challenge now, Schmidt says, is not processors. Or power supplies. Or storage. It's memory. Users simply want too much of it.

Applications are demanding more RAM than ever. And ironically, the very technologies IT has used to consolidate server sprawl and reduce power and cooling loads -- virtualization, multicore chips and blade servers -- have also increased the demand for memory. "The more processing power you put on a chip, the more you need to surround it with memory," says Rich Hetherington, chief architect and distinguished engineer at Sun.

While memory density continues to follow Moore's Law, the demand for memory is moving faster than the rate at which memory-chip density is increasing. That leaves system designers struggling to fit more and more dual in-line memory modules (DIMM) on smaller and smaller mother­boards.

IBM's high-end Intel-based System x3950 four-way servers are now being configured with as many as 64 DIMMs. And the need to free up more real estate for DIMMs led Sun to go with fatter server blades in its 8000 Series line, bucking the "smaller is better" trend.

Increasingly, IBM is shipping machines whose power requirements for memory far outstrip those for processors. "The ratio we're seeing now is the memory taking over 2 to 1. That's huge," Schmidt says. Depending on the system architecture, the power load for just one DIMM can be as high as 14 watts, according to AMD. In contrast, the chip maker's dual-core processor for the blade server market consumes 68 watts.