Cisco Systems OL-26646-01 manual Dimm Population Rules, Udimm

Chapter 3 Maintaining the Server

Installing or Replacing Server Components

DIMM Population Rules

Observe the following guidelines when installing or replacing DIMMs:

•Each CPU supports three memory channels.

–CPU1 supports channels A, B, and C.

–CPU2 supports channels D, E, and F

Note In a single-CPU system, the maximum number of DIMMs is six (only the slots supported by CPU1).

•Each channel has two DIMM slots (for example, channel A = slots A1 and A2).

–A channel can operate with one or two DIMMs installed.

–If a channel has only one DIMM, populate slot 0 first (the blue slot).

•When both CPUs are installed, populate the DIMM slots of each CPU identically.

–Fill blue slots in the channels first: A1, D1, B1, E1, C1, F1

–Fill black slots in the channels second: A2, D2, B2, E2, C2, F2

•In a single-CPU configuration, populate the channels for CPU1 only. Any DIMM installed in a DIMM socket for which the CPU is absent is not recognized.

•Although 1600 MHz DIMMs can be run in Power Savings 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.”) A 1600 MHz DIMM set to Power Savings Mode operates at 1066 MHz.

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

Table 3-3	DIMM Mixing Rules
DIMM Parameter Mixed		Mix Within Single Channel?	Mix Across Multiple Channels?
DIMM size (4, 8, 16 GB)		Yes—can be different sizes in	Yes—Can be different sizes in server.
		the channel.
DIMM speed (1333 or		No—Must be same speed in	No—Must be the same speed in server.
1600 MHz)		channel.
DIMM type (RDIMM,		No—Must be same type in	No—Must be the same type in server.
UDIMM)		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 2 or 4, as described in Memory Mirroring, page 3-22.

•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 configurations or at 1066 MHz in 2 DPC configurations.

–In Power Saving Mode (1.35 V operation), UDIMMs run at 1333 MHz in 1 DPC configurations or at 1066 MHz in 2 DPC configurations.

	Cisco UCS C22 Server Installation and Service Guide
OL-26646-01		3-21