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Cisco UCS C200 Server Installation and Service Guide
OL-20732-02
Chapter 3 Maintaining the Server
Installing or Replacing Components
Low-Voltage DIMM Considerations (Generation M2 Only)
The Generation M2 of this server can be ordered with low-voltage (1.35 V) DIMMs or standard-voltage
(1.5 V) DIMMs. Note the following considerations:
• Low-voltage DIMMs within the server must have the identical manufacturer, type, speed, and size.
• Low-voltage DIMMs and standard-voltage DIMMs can be mixed in the same server. Note that this
causes the system BIOS to default to standard-voltage operation (Performance Mode). That is, the
server cannot operate in Power Saving Mode unless all DIMMs are low-voltage DIMMs.
Note CPUs that have a maximum memory frequency less than 1333 MHz support LV DIMMs
operating in Power saving Mode only, and do not support Performance mode. However, if your
server has one of these CPUs, monitoring output for LV DIMMs will show identical voltages for
both Power Saving Mode and Performance Mode. In this case, Performance Mode is not active
and its fields only mirror the values from the Power Savings Mode fields.
• In Generation M2 only, there is a setting in the BIOS Setup utility that you can use to change the
DDR memory mode when the server has all low-voltage DIMMs installed. To access this setting,
follow these steps:
Step 1 Enter the BIOS setup utility by pressing the F2 key when prompted during bootup.
Step 2 Select the Advanced tab.
Step 3 Select Low Voltage DDR Mode.
Step 4 In the pop-up window, select either Power Saving Mode or Performance Mode.
• Power Saving Mode–Prioritizes low-voltage memory operation. This setting is available only if all
DIMMs installed are low-voltage DIMMs.
• Performance Mode–Prioritizes performance memory operation. If you mix low-voltage DIMM pairs
with standard-voltage DIMM pairs, the system defaults to this setting.
Step 5 Press F10 to save your changes and exit the setup utility.
Memory Mirroring and RAS
• The CPUs support memory mirroring only when Channels A and B on CPU 1 are populated with
DIMMs that are identical in configuration, size, and speed. Do not populate channel C. If three
channels are populated with DIMMs, memory mirroring is automatically disabled.
• If DIMMs on CPU 2 are populated, channels D and E must be populated with DIMMs that are
identical in configuration, size, and speed. Do not populate channel F. If three channels are
populated with DIMMs, memory mirroring is automatically disabled.
• If memory mirroring is used, the DRAM size is reduced by 50 percent for reasons of reliability.
Memory sparing is not supported.