Fb-Dimm Options For Lower Power Consumption - HP 226824-001 - ProLiant - ML750 Update Manual

ISS Technology Update

FB-DIMM options for lower power consumption

High memory capacity Intel® processor-based HP ProLiant servers have migrated toward high-speed, serial, Fully Buffered Dual
Inline Memory Module (FB-DIMM) technology, mainly because it delivers scalable bandwidth and memory capacity that is not
possible with traditional memory system architectures. The benefits of FB-DIMM technology also include simplified system board
design and improved reliability. To deliver these benefits, the FB-DIMM architecture uses point-to-point serial links to connect the
memory controller to an advanced memory buffer (AMB) chip that resides on each FB-DIMM.
The high-speed serial interface of the AMB causes the FB-DIMM to consume almost 5 Watts more than a typical registered
Double Data Rate 2 (DDR2) DIMM. The AMB power consumption also causes the FB-DIMM to get hotter; therefore, a heat
spreader is required to help draw heat away from the module (Figure 3-1). Notably, the energy consumption gap between FB-
DIMMs and DDR2 DIMMs decreases as the load on the memory subsystem increases because the power use of the AMB
doesn't increase significantly with demand.
To mitigate the power use and heat issues with standard FB-DIMMs, HP has launched lower-power FB-DIMMs that use between
10 and 20 percent less power at the same memory density. Of course, the actual power savings will be based on the system
configuration and work load. However, the percentage of savings should be fairly constant for a given system.
Another option to decrease the memory subsystem power consumption is to use fewer FB-DIMMs of higher capacity. For
example, replacing four 2-GB FB-DIMMs with two 4-GB DIMMs will basically eliminate the power use and heat generation of
two AMBs. Additional power savings are realized because the DRAM power consumption from one 4-GB FB-DIMM is less than
the DRAM power consumption from two 2-GB FB-DIMMs. The total power savings, while quite significant, will vary based on
system configuration and work load.
Figure 3-1. FB-DIMM with full module heat spreader
Additional resources
For additional information on the topics discussed in this article, visit the following link:
Resource
"Fully-Buffered DIMM technology in
HP ProLiant servers" technology
brief
Power calculator for HP ProLiant
servers that support FB-DIMMs
URL
http://h18004.www1.hp.com/products/servers/technology/white
papers/adv-technology.html#mem
http://h30099.www3.hp.com/configurator/calc/Power%20Calcul
ator%20Catalog.xls
Volume 7, Number 1
8