CONFIGURATION GUIDE
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NEC Express5800/A2040c, A2020c, A2010c, A1040c
NEC Corporation
Rev.2.0
–Sep. 2015
54
2.4 Memory Rank Sparing
“Memory Rank Sparing” is the feature to keep operation (for high availability); by having 1 or 2 memory ranks
of 2 DIMMs in one memory channel as a spare, when detecting errors at memory rank in operation,
automatically switching to a spare rank. To use this feature, need to order memory set including 4 DIMMs per
set
Memory Rank Sparing for each Memory Configuration Mode:
Independent Mode: one or 2 memory rank out of 2 DIMMs in one memory channel is assigned as a
spare.
Lockstep Mode: one or 2 memory rank is assigned as a spare out of either a memory pair on CH0 and
CH1 OR a memory pair on CH02 and CH03.
NOTE:
Cannot mix RDIMM and LRDIMM in a server
When using Memory Rank Sparing, the available memory capacity reduces by the capacity of spare
memory rank:
Available Memory Capacity:
1/2 of physical memory (8GB RDIMM)
1/2, 3/4 of physical memory (16GB RDIMM)
Lockstep Mode + Memory Rank Sparing is a standard setting at the server delivery. To use Independent
Mode, need to change the mode from BIOS set-up menu.
Cannot use both Memory Mirroring and Memory Rank Sparing at the same time.
For DIMM installation priority/order, (1) to install larger DIMM first, and (2) to install DIMMs to the sockets in
the priority/order shown in the figure below.
DIMM Installation Order for Memory Rank Sparing
