Lenovo Flex System x440 Compute Node Installation And Service Manual page 905

Table 12. Memory-channel configuration (continued)
Microprocessor
Microprocessor 4
The following notes describe information that you must consider when you install memory:
• You cannot mix RDIMMs, LRDIMMs and UDIMMs in the same compute node.
• UDIMMs are not supported at three DIMMs per channel.
• A total of eight ranks on each channel is supported.
• If a quad-rank DIMM is installed, install it in the connector at the end of the memory channel.
• If a channel has one or more quad-rank RDIMMs, only two DIMMs per channel is supported. The quad-
rank, eight rank per channel limitation only applies to RDIMMs. Quad-rank LRDIMMs can be installed at
three DIMMs per channel since the processor recognizes LRDIMMs as dual-rank DIMMs.
There are three memory modes:
• Independent-channel mode: Independent-channel mode provides a maximum of 384 GB of usable
memory per processor and 1536 GB of usable memory with all four processors installed using 32 GB
DIMMs. DIMMs must be first installed in the last physical DIMM connector of each channel. DIMMs should
also be installed one DIMM per channel first. The best performance is seen with an even memory
distribution among all four channels on the microprocessor. DIMMs can be installed without matching
sizes. Individual channels may run at different DIMM timings, but all channels must run at the same
interface frequency. DIMMs with different timing parameters can be installed in different connectors of the
same channel, but only timings that support the slowest DIMM are applied to all the DIMMs. Faster
DIMMs operate at timings that are supported by the slowest installed DIMM.
• Mirrored-channel mode: In mirrored-channel mode, memory is installed in pairs. Both DIMMs in a pair
must be identical in capacity, type, and rank count. The channels are grouped in pairs with each channel
receiving the same data. One channel is used as a backup of the other, which provides redundancy. In
mirrored-channel mode, memory must be installed in pairs. The memory content is mirrored between
channel 0 and channel 1 and between channel 2 and channel 3. Mirrored-channel mode requires that
channel 0 and channel 1, and channel 2 and channel 3 are be populated identically in regard to size and
organization. DIMM connector populations within a channel do not have to be identical, but the same
DIMM connector location across channel 0 and channel 1 and across channel 2 and channel 3 must be
populated in the same way. The effective memory that is available to the system is only half of what is
installed.
• Rank-sparing mode: In rank-sparing mode, one memory DIMM rank serves as a spare of the other ranks
on the same channel. The spare rank is held in reserve and is not used as active memory. The spare rank
must have identical or larger memory capacity than all the other active DIMM ranks on the same channel.
After an error threshold is surpassed, the contents of that rank are copied to the spare rank. The failed
rank of DIMMs is taken offline, and the spare rank is put online and used as active memory in place of the
failed rank. The following notes describe additional information that you must consider when you select
rank-sparing memory mode:
– Memory sparing on one channel is independent of the sparing on all other channels.
– You can use the Setup utility to determine the status of the DIMM ranks.
Memory channel
Channel 0
Channel 2
Channel 3
Channel 1
Channel 0
.
Chapter 7 Installing, removing, and replacing compute node components
DIMM connectors
34, 35, and 36
37, 38, and 39
40, 41, and 42
43, 44, and 45
46, 47, and 48
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