Product guide
High-performance blade server optimized for virtualization
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7.
memory controllers and faster DDR3 1333MHz memory. Throughput at 800MHz is 25 gigabytes per
second (GBps); at 1066MHz it’s 32GBps; and at 1333MHz it’s 35GBps. This improvement translates
into improved application performance and scalability.
Memory interleaving refers to how physical memory is interleaved across the physical DIMMs. A
balanced system provides the best interleaving. A Xeon 5600 processor-based system is balanced when
all memory channels for a socket have the same amount of memory.
In the case of HS22V, which has a balanced DIMM layout, it is easy to balance the system for all three
memory frequencies. The recommended DIMM population is shown below, assuming DIMMs with
identical capacities.
Desired Memory Speed DIMMs per Channel DIMM Slots to Populate
1333MHz 1 3, 6, 9, 12, 15, and 18
1066MHz 2 2, 3, 5, 6, 8, 9, 11, 12, 14, 15, 17, and 18
800MHz 3 All slots
A memory rank is simply a segment of memory that is addressed by a specific address bit. DIMMs
typically have 1, 2 or 4 memory ranks, as indicated by their size designation.
A typical memory DIMM description is 2GB 4Rx8 DIMM
The 4R designator is the rank count for this particular DIMM (R for rank = 4)
The x8 designator is the data width of the rank
It is important to ensure that DIMMs with appropriate number of ranks are populated in each channel for
optimal performance. Whenever possible, it is recommended to use dual-rank DIMMs in the system.
Dual-rank DIMMs offer better interleaving and hence better performance than single-rank DIMMs. For
instance, a system populated with six 2GB dual-rank DIMMs outperforms a system populated with six
2GB single-rank DIMMs by 7% for SPECjbb2005. Dual-rank DIMMs are also better than quad-rank
DIMMs because quad-rank DIMMs will cause the memory speed to be down-clocked.
Another important guideline is to populate equivalent ranks per channel. For instance, mixing one
single-rank DIMM and one dual-rank DIMM in a channel should be avoided.
Note: It is important to ensure that all three memory channels in each processor are populated. The
relative memory bandwidth decreases as the number of channels populated decreases. This is because
the bandwidth of all the memory channels is utilized to support the capability of the processor. So, as the
channels are decreased, the burden to support the requisite bandwidth is increased on the remaining
channels, causing them to become a bottleneck.
For peak performance:
Always populate both processors with equal amounts of memory to ensure a balanced NUMA system.
Always populate all 3 memory channels on each processor with equal memory capacity.
Populate an even number of ranks per channel.
Use dual-rank DIMMs whenever appropriate.
For optimal 1333MHz performance, populate with 6 dual-rank DIMMs (3 per processor, 1 per
channel).
For optimal 1066MHz performance, populate with 12 dual-rank DIMMs (6 per processor, 2 per
channel).
For optimal 800MHz performance with high DIMM counts, populate with 18 dual-rank or quad-rank
DIMMs (9 per processor) and clock memory down to 800MHz in BIOS.
With the above rules, it is not possible to have a performance-optimized system with 4GB, 8GB,
16GB, or 128GB. With 3 memory channels and interleaving rules, configure systems with 6GB, 12GB,
18GB, 24GB, 48GB, 72GB, 96GB, etc., for optimized performance.
Power guidelines:
Fewer larger DIMMs (for example 6 x 4GB DIMMs vs. 12 x 2GB DIMMs will generally have lower
power requirements
x8 DIMMs (x8 data width of rank) will generally draw less power than equivalently sized x4 DIMMs
Reliability guidelines:
Using fewer, larger DIMMs (for example 6 x 4 GB DIMMs vs. 12 x 2GB DIMMs is generally more
reliable
Xeon 5600 series and 5500 series memory controllers support IBM Chipkill memory protection
technology with x4 DIMMs (x4 data width of rank), but not with x8 DIMMs