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Cisco UCS C24 Server Installation and Service Guide
OL-26647-01z
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.
If you choose to enable memory mirroring, populate the DIMM slots in the order shown in Table 3-4 or
Table 3-5.
DIMM Replacement Procedure
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 Shutting Down and Powering Off the Server, page 3-6.
b. Slide the server out the front of the rack far enough so that you can remove the top cover. You might
have to detach cables from the rear panel to provide clearance.
Caution If you cannot safely view and access the component, remove the server from the rack.
c. Remove the top cover as described in Removing and Replacing the Server Top Cover, page 3-7.
d. Remove PCIe riser 1 to provide clearance and set it aside on an antistatic surface (see Replacing a
PCIe Riser, page 3-32).
e. Remove the plastic air baffle that covers the DIMM slots and CPUs.
f. Open the ejector levers at both ends of the DIMM slot, then lift the DIMM out of the slot.
Step 2 Install a new DIMM:
Ta b l e 3-4 Two-CPU Memory Mirroring DIMM Population
Number of DIMMs
per CPU CPU 1 Population CPU2 Population
2 A0; B0 D0; E0
4 A0, B0; A1, B1 D0, E0; D1, E1
Ta b l e 3-5 One-CPU Memory Mirroring DIMM Population
Number of DIMMs
per CPU CPU 1 Population CPU2 Population
2 A0; B0 CPU2 slots not available
4 A0, B0; A1, B1 CPU2 slots not available