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Cisco UCS C260 Server Installation and Service Guide
OL-24342-01
Chapter 3 Maintaining the Server
Installing or Replacing Server Components
DIMM Population Rules
Observe the following guidelines when installing or replacing DIMMs:
•
The minimum memory riser configuration is one matched pair of memory risers on either CPU1 or
CPU2. See
Replacing Memory Risers, page 3-21
for more detail on memory riser population.
•
Matched pairs of risers on paired DDR3 channels must have identical DIMM configurations.
For example, the DIMM configurations must be identical on risers in A0:A1; however, the A0:A1
configurations do not have to be identical with the B0:B1 configurations.
•
Any DIMM installed in a memory riser corresponding to an empty CPU slot becomes inaccessible.
•
Two-DIMM memory riser population rules are as follows:
–
The two-DIMM riser can operate with one or two DIMMs installed.
–
Both DIMMs installed on any one riser must be identical.
–
Populate the slots in this order: 1, 2. See
Figure 3-16
.
•
Four-DIMM memory riser population rules are as follows:
–
The four-DIMM riser can operate with one, two, three, or four DIMMs installed.
–
All DIMMs installed on any one riser must be identical.
–
Populate the slots in this order: 1, 2, 3, 4. See
Figure 3-16
.
DIMM Sparing and Rank Sparing
DIMM and rank sparing can be enabled in the BIOS configuration utility.
Sparing involves utilizing one of the DIMM pairs or rank pairs within each memory riser as a spare unit.
When any of the other DIMM pairs within the same memory riser experiences errors beyond a
pre-defined threshold, it fails over to the spare DIMM pair. Spared DIMMs and ranks are hidden from
the user and the OS so that the BIOS can migrate to a spare unit when it finds degrading DIMMs.
When sparing is enabled, the available system memory is lesser than the total installed memory.
•
When using DIMM sparing, the available memory equals total installed memory minus the size of
spared DIMMs.
•
When using rank sparing, available memory equals total installed memory minus the size of the
spared ranks. Rank size equals DIMM size divided by the number of ranks.
