Hardware options installation 49
However, the server cannot support DIMM sparing in this example if the 2-GB DIMMs are populated
in the 1A/8A pair locations and the 4-GB DIMMs are populated in any of the remaining DIMM pair
locations. This is because it violates the rule requiring that the spare rank size of DIMM pair 1A/8A
(1 GB) be equal to or larger than the single rank size of the other DIMM pair locations, since the
rank size of a 4-GB DIMM in pairs B, C, or D would be larger (2 GB) than the spare rank size of the
2-GB DIMM pair in 1A/8A (1 GB).
Mirrored Memory population guidelines
Errors that are not corrected by ECC or SDDC cannot be corrected by Online Spare memory. By
providing added redundancy in the memory sub-system, Mirrored Memory provides the greatest
protection against memory failure beyond ECC, SDDC, and Online Spare memory.
In Mirrored Memory mode, each Lockstep DIMM pair of a memory controller (of a memory cartridge
connected to a processor) has a mirrored DIMM pair on the other memory cartridge of the same
processor.
Upon detecting an uncorrectable memory error from a DIMM pair of a memory cartridge, the processor
avoids a system crash by reading the mirrored DIMM pairs from the other memory cartridge. In this case,
the system management routine disables the failed DIMM. Further memory reads and writes will only
occur on the mirrored DIMM pairs.
The exceptions to Mirrored Memory mode are the following:
• In Mirrored Memory mode, half of the memory is allocated to memory protection.
• The available memory bandwidth is reduced by up to 50% in this mode.
• Mirrored Memory mode, Online Spare mode, Hemisphere mode, and interleaving cannot be
enabled simultaneously.
To configure memory for Mirrored Memory mode, observe these additional constraints:
• For the server to support Mirrored Memory, all processors must have a valid mirroring configuration.
• The minimum allowable configuration is two memory cartridges per processor.
• Both memory cartridges for each processor must be populated with the same DIMM configurations.
• Although this configuration requirement is the same for Hemisphere mode and Mirrored Memory
mode, only one of the two modes can be enabled at a given time.
Installing memory
1. Power down the server (on page 25).
2. Remove the processor memory drawer (on page 27).
CAUTION: To prevent damage to the processor memory drawer cover, be sure the handle of
the processor memory drawer is fully open before removing the cover.
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