Specifications
3-27
Cisco UCS C240 Server Installation and Service Guide
OL-25761-01z
Chapter 3 Maintaining the Server
Installing or Replacing Server Components
Memory Mirroring
When memory mirroring is enabled, the memory subsystem simultaneously writes identical data to two
channels. If a memory read from one of the channels returns incorrect data due to an uncorrectable
memory error, the system automatically retrieves the data from the other channel. A transient or soft
error in one channel does not affect the mirrored data, and operation continues unless there is a
simultaneous error in exactly the same location on a DIMM and its mirrored DIMM. Memory mirroring
reduces the amount of memory available to the operating system by 50% because only one of the two
populated channels provides data.
Note You must choose to enable memory mirroring in the server BIOS setup utility, under
Advanced > Memory Configuration > Mirroring.
If you choose to enable memory mirroring, populate the DIMM slots in the order shown in Table 3-5.
DIMM Replacement Procedure
This section includes the following topics:
• Identifying a Faulty DIMM, page 3-27
• Replacing DIMMs, page 3-27
Identifying a Faulty DIMM
Each DIMM slot has a corresponding DIMM fault LED. See Figure 3-3 for the locations of these LEDs.
The LEDs light amber to indicate a faulty DIMM. To operate these LEDs from the SuperCap power
source, remove AC power cords and then press the Identification button. See also
Internal Diagnostic
LEDs, page 3-6.
Replacing DIMMs
To install a DIMM assembly, follow these steps:
Step 1 Remove the DIMMs that you are replacing:
a. Power off the server as described in the “Shutting Down and Powering Off the Server” section on
page 3-7.
Ta b l e 3-5 Memory Mirroring DIMM Population
Number of
DIMMs per CPU
CPU 1 Population CPU2 Population
4 A1, B1; A2, B2 E1, F1; E2, F2
6 A1, B1; A2, B2; A3, B3 E1, F1; E2, F2; E3, F3
8 A1, B1; C1, D1; A2, B2; C2, D2 E1, F1; G1, H1; E2, F2; G2, H2
10 A1, B1; C1, D1; A2, B2; C2, D2; A3, B3 E1, F1; G1, H1; E2, F2; G2, H2; E3, F3
12 A1, B1; C1, D1; A2, B2; C2, D2; A3, B3;
C3, D3
E1, F1; G1, H1; E2, F2; G2, H2; E3, F3;
G3, H3