Cisco UCS C3160, Installation And Service Manual

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Cisco UCS C3160 Rack Server Installation and Service Guide
OL-32062-01
Chapter 3 Maintaining the System
Installing or Replacing System Components
Memory Mirroring Mode
When you enable memory mirroring mode, the memory subsystem simultaneously writes identical data
to two channels. If a memory read from one of the channels returns incorrect data due to an uncorrectable
memory error, the system automatically retrieves the data from the other channel. A transient or soft
error in one channel does not affect the mirrored data, and operation continues.
Memory mirroring reduces the amount of memory available to the operating system by 50 percent
because only one of the two populated channels provides data.
Lockstep Channel Mode
When you enable lockstep channel mode, each memory access is a 128-bit data access that spans four
channels.
Lockstep channel mode requires that all four memory channels on a CPU must be populated identically
with regards to size and organization. DIMM socket populations within a channel do not have to be
identical but the same DIMM slot location across all four channels must be populated the same.
For example, DIMMs in sockets A1, B1, C1, and D1 must be identical. DIMMs in sockets A2, B2, C2,
and D2 must be identical. However, the A1-B1-C1-D1 DIMMs do not have to be identical with the
A2-B2-C2-D2 DIMMs.
Table 3-5 DIMM Mixing Rules
DIMM Parameter DIMMs in the Same Channel DIMMs in the Same Bank
DIMM Capacity:
RDIMM = 8 or 16 GB
You can mix different capacity DIMMs in
the same channel (for example, A1, A2).
•
You can mix different capacity DIMMs
in the same bank. However, for optimal
performance DIMMs in the same bank
(for example, A1, B1, C1, D1) should
have the same capacity.
DIMM Speed:
1600- or 1866-MHz
You can mix speeds, but DIMMs will run at
the speed of the slowest DIMMs/CPUs
installed in the channel. You can mix speeds, but DIMMs will run at
the speed of the slowest DIMMs/CPUs
installed in the bank.
DIMM Type:
RDIMMs
You cannot mix DIMM types in a channel. You cannot mix DIMM types in a bank.