Cisco UCS C240 M4, Installation And Service Manual

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Cisco UCS C240 M4 Server Installation and Service Guide
OL-32474-01
Chapter 3 Maintaining the Server
Installing or Replacing Server Components
Memory Mirroring and RAS
The Intel E5-2600 CPUs within the server support memory mirroring only when an even number of
channels are populated with DIMMs. If one or three channels are populated with DIMMs, memory
mirroring is automatically disabled. Furthermore, if memory mirroring is used, DRAM size is reduced
by 50 percent for reasons of reliability.
For details on populating recommended memory mirroring configurations, see the specification sheet for
the server:
•
Cisco UCS C240 M4 High Density Rack Server (Small Form-Factor Disk Drive Model)
Specification Sheet
• Cisco UCS C240 M4 High Density Rack Server (Large Form-Factor Disk Drive Model)
Specification Sheet
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.
Table 3-5 DIMM Mixing Rules for C240 M4 Servers
DIMM Parameter DIMMs in the Same Channel DIMMs in the Same Bank
DIMM Capacity:
RDIMM = 8 or 16 GB
LRDIMM = 32 or 64 GB
•
You can mix different capacity
DIMMs in the same channel (for
example, A1, A2, A3).
•
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:
2133 or 2400 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 or LRDIMMs
You cannot mix DIMM types in a channel. You cannot mix DIMM types in a bank.