Lenovo Flex System x220 Installation And Service Manual page 664

microprocessors (using 16 GB DIMMs). See "Independent-channel mode" on page 658 for additional
information.
• Rank-sparing mode: In rank-sparing mode, one memory DIMM rank serves as a spare of the other ranks
on the same channel. The spare rank is held in reserve and is not used as active memory. The spare rank
must have identical or larger memory capacity than all the other active DIMM ranks on the same channel.
After an error threshold is surpassed, the contents of that rank are copied to the spare rank. The failed
rank of DIMMs is taken offline, and the spare rank is put online and used as active memory in place of
the failed rank. See "Rank-sparing mode" on page 658 for additional information.The following notes
describe additional information that you must consider when you select rank-sparing memory mode:
– Memory sparing on one channel is independent of the sparing on all other channels.
– You can use the Setup utility to determine the status of the DIMM ranks.
– If only one DIMM is present in a channel and the DIMM is dual or single rank, then sparing mode
should not be enabled.
• Mirrored-channel mode: In mirrored-channel mode, memory is installed in pairs. Each DIMM in a pair
must be identical in capacity, type, and rank count. The channels are grouped in pairs with each channel
receiving the same data. One channel is used as a backup of the other, which provides redundancy.
For each microprocessor, the memory contents on channel 2 are duplicated in channel 3, channel 1
is unused. The effective memory that is available to the system is only half of what is installed. See
"Mirrored-channel mode" on page 659 for additional information.
One DIMM for each microprocessor is the minimum requirement. However, for optimal performance, install
DIMMs in sets of four so that you distribute memory equally across all channels. If two microprocessors are
installed, distribute memory across all channels and equally between the microprocessors. Install DIMMs in
the order as indicated in the following table for independent-channel mode and rank-sparing mode.
To install a DIMM, complete the following steps:
Step 1. Remove the cover (see "Removing the compute node cover" on page 643).
Step 2. Read the documentation that comes with the DIMM.
Step 3. Remove the air baffle installed over the DIMM connector.
Left
air baffle
Step 4. Locate the DIMM connectors (see "System-board connectors" on page 17). Determine which
DIMM connector you want to install the DIMM in.
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Flex System x220 Compute Node Installation and Service Guide
Right
air baffle