3-26
Cisco UCS C240 Server Installation and Service Guide
OL-25761-01
Chapter 3 Maintaining the Server
Installing or Replacing Server Components
•
Any DIMM installed in a DIMM socket for which the CPU is absent is not recognized. In a
single-CPU configuration, populate the channels for CPU1 only.
•
Although 1600 MHz DIMMs can be run in Power Saving Mode (low-voltage 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
.”) A 1600 MHz DIMM with DDR mode set to Power
Saving Mode operates at 1066 MHz.
•
Observe the DIMM mixing rules shown in
Table 3-4
.
•
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, 8, or 12 as described in
Memory Mirroring, page 3-27
.
•
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.
–
UDIMMs do not support 3 DIMMs per channel (3 DPC) configurations.
–
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
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.
Table 3-4
DIMM Mixing Rules
DIMM Parameter Mixed
Mix Within Single Channel?
Mix Across Multiple Channels?
DIMM size (4, 8, 16 GB)
No—Must be same size in
channel.
Yes—Can be different sizes in
server.
1
1.
Note: Although you can mix DIMM sizes across channels, this will result in less than optimal performance. For optimal
performance, all DIMMs in the server should be identical.
DIMM speed (1333 or
1600 MHz)
No—Must be same speed in
channel.
No—Must be the same speed in
server.
DIMM type (U-DIMM or
R-DIMM)
No—Must be same type in
channel.
No—Must be the same type in server.
