Product guide

Ultrascalability combined with extreme availability
features and industry-leading performance
Please see the Legal Information section for important notices and information.
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enhanced CRC protection, data retry on error detect and buffer registers for improved fault
isolation.
An 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.
Notes: DIMMs must be installed in matching pairs. Also, each CPU requires at least 2
DIMMs. It is important to ensure that all 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:
• Populate both processors with equal amounts of memory to enable a balanced NUMA
system.
• Populate both memory controllers within a processor with equal memory capacity.
• Populate an even number of ranks per channel.
• Use dual-rank DIMMs whenever appropriate.
Power guidelines:
• Fewer larger DIMMs (for example 8 x 4GB DIMMs vs. 16 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 8 x 4 GB DIMMs vs. 16 x 2GB DIMMs is generally
more reliable
• Memory controllers support IBM Chipkill memory protection technology with x4 DIMMs (x4
data width of rank) and x8 DIMMs
For increased availability beyond Chipkill error correction, the eX5 servers offer additional
levels of IBM Active Memory protection:
Memory ProteXion technology provides multichip error protection and works in conjunction
with Chipkill technology—which provides multibit protection per chip—and standard ECC
protection, to provide multi-level memory correction.
Memory scrubbing is an automatic daily test of all system memory. It detects and reports
memory errors that might be developing before they cause a server outage. Memory
scrubbing and Memory ProteXion work together. When a bit error is detected, memory
scrubbing determines whether the error is recoverable. If so, the Memory ProteXion feature
will write the data to new location; if it is not recoverable, scrubbing sends an alert to light
path diagnostics, which then notifies IBM Systems Director.
Memory mirroring works much like disk mirroring. The total memory is divided into two
channels. Data is written concurrently to both channels. If a DIMM fails in one of the DIMMs
in the primary channel, it is instantly disabled and the mirrored (backup) memory in the other
channel becomes active (primary) until the failing DIMM is replaced. With mirroring enabled,
one-half of total memory is available for use. (Note: Due to the double writes to memory,
performance is affected.) Mirroring is handled at the hardware level; no operating system
support is required.
Memory rank sparing works somewhat like mirroring, except instead of having an entire
memory channel reserved, two memory ranks per memory card are configured as spares. In
the event of a memory failure on the same card, one of the spare ranks is automatically used
in place of the failing one. (Rank sparing and mirroring are mutually exclusive.)
Memory is available in 2GB, 4GB, 8GB, 16GB and 32GB DIMMs
1
.
High
-
Performance Scalability
Scalability can be achieved in two different ways. You can choose to scale “natively” by
simply cabling two chassis together via the Quick Path Interconnect (QPI) ports, for 8 sockets
and 128 DIMMs. Or, you can scale via MAX5, adding memory capacity for increased
performance. This configuration cables a 4-socket chassis to a MAX5. You can also go
further, with two chassis and two MAX5 units, all interconnected
2
. The two MAX5 units are
cabled together using our exclusive EXA Scalability Kit. The result is an
8
-
socket
,
192 DIMM
1
32GB DIMMs supported in machine type 7143 only