Lenovo Flex System x480 X6 Compute Node Installation And Service Manual page 1004

• Only 8 GB and 16 GB RDIMMs are supported if you also install eXFlash DIMMs.
• 64 GB LR-DIMMs are not supported in a four-node complex.
• You cannot mix RDIMMs and LRDIMMs in the same compute node.
• You cannot mix RDIMMs and LRDIMMs in a scalable partition within a multi-node complex.
• A total of eight ranks on each channel is supported.
• DIMMs of mixed speed can be installed on different DIMM slots within the same channel, but the DIMMs
operate at the speed of the slowest DIMM.
• If you install a quad-rank or octal-rank DIMM, install it in the connector at the end of the memory channel.
• If a channel has one or more quad-rank RDIMMs, only two DIMMs per channel are supported. The
quad-rank, eight rank per channel limitation only applies to RDIMMs. You can install three quad-rank
LRDIMMs because the microprocessor accesses LRDIMMs as dual-rank DIMMs.
There are two memory modes:
• Independent-channel mode: Independent-channel mode provides high performance memory capability.
The memory channels can be populated with DIMMs in any order in independent mode. You can populate
all four channels on each microprocessor in any order with no matching requirements. Individual channels
can run at different DIMM timings, but all channels must run at the same interface frequency.
• Lockstep mode: Lockstep mode provides extensive memory protection through double device data
correction (DDDC). DDDC allows up to two sequential memory DRAM chip failures without affecting
overall system performance. The memory controller handles all cache lines across two DDR3 channels
controlled by one scalable memory buffer. The SMI2 channel operates at the DDR3 transfer rate.
Optionally, you can enable mirrored-channel memory or rank-sparing memory to provide additional reliability:
• Mirrored-channel memory: In mirrored-channel memory, the contents of memory is mirrored between
SMI2 channels. As a result, the total available memory is half of the physical memory installed. The
maximum effective memory is 1.5 TB (using 64 GB DIMMs). To enable mirrored-channel memory, memory
on each SMI2 channel must be populated with DIMMs that have the same feature set (capacity, type, and
rank count). The DIMM channels can have memory with different feature sets, but the DIMM slots across
each SMI2 channel must be populated with DIMMs that have the same feature set.
• Rank-sparing memory: In rank-sparing memory, 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 compared to 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. The following notes describe additional information that you must
consider when you select rank-sparing memory:
– A minimum of two single-rank DIMMs per channel must be populated to use rank-sparing memory.
– You can use rank-sparing memory with single multi-rank DIMMs.
– Rack-sparing memory 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 you install LR-DIMMs, more than one rank is held in reserve.
– Rank sparing is not supported when mirroring is enabled.
Install DIMMs in the order that is indicated in the following table for independent-channel mode.
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Lenovo Flex System x280 X6, x480 X6, and x880 X6 Compute Node Installation and Service Guide