Cisco Systems UCSSP6C220E, 9266CV-8i Enabling Low-Voltage DIMM Operation Power Saving Mode, 3-20

Chapter 3 Maintaining the Server

Installing or Replacing Server Components

•Although 1600 MHz DIMMs can be run in Power Saving Mode (1.35 V operation), 1600 MHz operation is supported only when the DDR mode is set to Performance Mode (see “Enabling Low-Voltage DIMM Operation (Power Saving Mode).”) When the DDR mode is set to Power Saving Mode, a 1600 MHz DIMM operates at 1066 MHz.

•Observe the DIMM mixing rules shown in Table 3-4.

Table 3-4	DIMM Mixing Rules
DIMM Parameter Mixed		Mix Across Single Channel?	Mix Across Multiple Channels?
DIMM size (4, 8, 16, or		No—Must be same size in	Yes—Can be different sizes in server.
32 GB)		channel.
DIMM speed (1333 or		No—Must be same speed in	No—Must be the same speed in server.
1600 MHz)		channel.
DIMM type (U-DIMM or		No—Must be same type in	No—Must be the same type in server.
R-DIMM)		channel.

•Memory mirroring reduces the amount of memory available by 50% because only one of the two populated channels provides data. When memory mirroring is enabled, DIMMs must be installed in sets of 4, 6, or 8 as described in Memory Mirroring, page 3-21.

•Note the following restrictions when using UDIMMs. Even though a UDIMM might be rated at 1600 MHz, actual operational speeds are slower because of the Intel implementation.

–In Performance Mode (1.5 V operation), UDIMMs run at 1333 MHz in 1 DPC and 2 DPC configurations.

–In Power Saving Mode (1.35 V operation), UDIMMs run at 1066 MHz in 1 DPC and 2 DPC configurations.

Enabling Low-Voltage DIMM Operation (Power Saving Mode)

You can enable low voltage (1.35 V) DIMM operation for all DIMMs in the server. There is a setting in the BIOS Setup utility that you can use to change the DDR memory mode to Power Saving mode, as described in the following procedure:

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 or Performance Mode:

•Power Saving Mode–Prioritizes low-voltage memory operation.

•Performance Mode–Prioritizes performance memory operation. If you mix low-voltage DIMMs with standard DIMMs, the system defaults to this setting.

Step 5 Press F10 to save your changes and exit the setup utility.

	Cisco UCS C220 Server Installation and Service Guide
3-20	OL-25760-01