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DDR5 RDIMMs mixed with CXL memory modules

This section contains information about how to install DDR5 RDIMMs mixed with CXL memory modules (CMMs) properly.

  • Servers with Compute Complex Neptune Core Module do not support CMMs.

  • CMM channel: number of devices per root port, with root ports separated by +, e.g. 2+2+2+2 = four root ports populated with two devices per root port

  • CMM modes:

    • 1LM+Vol = Native DDR5 (1LM) and (volatile) CMM visible to software (SW) as separate tiers, separately interleaved

    • Hetero x12 = DDR5 and (volatile) CMM interleaved together in one 12-way set

  • For CMM configurations, see E3.S backplane cable routing: E3.S chassis without Compute Complex Neptune Core Module.

  • To set the CMM mode, go to UEFI Setup > System Settings > Memory > CXL Memory Module > Memory Mode.

Table 1. Installation rule for one processor (processor 1)
DDR5 RDIMMsCMM
Slot 0 DIMMsSlot 1 DIMMsRDIMM modeCMM modeCMM capacity per moduleCMM channels
8 x 128 GB (2Rx4)N/AIndependent/mirroring1LM+Vol128 GB2, 2+2, or 2+2+2
N/AIndependentHetero128 GB2+2
8 x 128 GB (2Rx4)Independent/mirroring1LM+Vol128 GB2, 2+2, or 2+2+2
8 x 64 GB (2Rx4)N/AIndependent/mirroring1LM+Vol128 GB2, 2+2, or 2+2+2
8 x 64 GB (2Rx4)
8 x 96 GB (2Rx4)N/AIndependent/mirroring1LM+Vol96 GB2, 2+2, or 2+2+2
8 x 96 GB (2Rx4)
Table 2. Installation rule for two processors (processor 1 and processor 2)
DDR5 RDIMMsCMM per socket
Slot 0 DIMMsSlot 1 DIMMsRDIMM modeCMM modeCMM capacity per moduleCMM channels
16 x 128 GB (2Rx4)N/AIndependent/mirroring1LM+Vol128 GB2, 2+2, or 2+2+2
N/AIndependentHetero128 GB2+2
16 x 128 GB (2Rx4)Independent/mirroring1LM+Vol128 GB2, 2+2, or 2+2+2
16 x 64 GB (2Rx4)N/AIndependent/mirroring1LM+Vol128 GB2, 2+2, or 2+2+2
16 x 64 GB (2Rx4)
16 x 96 GB (2Rx4)N/AIndependent/mirroring1LM+Vol96 GB2, 2+2, or 2+2+2
16 x 96 GB (2Rx4)