Cisco UCS C240 M4 Installation And Service Manual page 62
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Installing or Replacing Server Components
Table 3-5
DIMM Mixing Rules for C240 M4 Servers
DIMM Parameter
DIMM Speed:
2133 or 2400 MHz
DIMM Type:
RDIMMs or LRDIMMs
Memory Mirroring
When memory mirroring is enabled, 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 unless there is a
simultaneous error in exactly the same location on a DIMM and its mirrored DIMM.
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.
Note
You must choose to enable memory mirroring in the server BIOS setup utility, under
Advanced > Memory Configuration > Mirroring.
If you choose to enable memory mirroring, populate the DIMM sockets in the order shown in
Table 3-6
Number of
DIMMs per CPU
4
6
8
10
12
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 regard to size and organization. DIMM socket populations within a channel (for example, A1, A2,
A3) 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.
Cisco UCS C240 M4 Server Installation and Service Guide
3-22
DIMMs in the Same Channel
You can mix speeds, but DIMMs will run at
the speed of the slowest DIMMs/CPUs
installed in the channel.
You cannot mix DIMM types in a channel. You cannot mix DIMM types in a bank.
Memory Mirroring DIMM Population
CPU 1 Population
A1, B1; A2, B2
A1, B1; A2, B2; A3, B3
A1, B1; C1, D1; A2, B2; C2, D2
A1, B1; C1, D1; A2, B2; C2, D2; A3, B3 E1, F1; G1, H1; E2, F2; G2, H2; E3, F3
A1, B1; C1, D1; A2, B2; C2, D2; A3, B3;
C3, D3
Chapter 3
Maintaining the Server
DIMMs in the Same Bank
You can mix speeds, but DIMMs will run at
the speed of the slowest DIMMs/CPUs
installed in the bank.
CPU2 Population
E1, F1; E2, F2
E1, F1; E2, F2; E3, F3
E1, F1; G1, H1; E2, F2; G2, H2
E1, F1; G1, H1; E2, F2; G2, H2; E3, F3;
G3, H3
Table
3-6.
OL-32474-01
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