Hardware options installation 49
Online spare memory protection dedicates one rank of each memory channel for use as spare memory.
The remaining ranks are available for OS and application use. If correctable memory errors occur at a rate
higher than a specific threshold on any of the non-spare ranks, the server automatically copies the
memory contents of the degraded rank to the online spare rank. The server then deactivates the failing
rank and automatically switches over to the online spare rank.
Mirrored Memory
Errors that are not corrected by ECC or SDDC cannot be corrected by Online Spare memory. Mirrored
Memory provides the greatest protection against memory failure beyond ECC, SDDC, and Online Spare
memory by providing added redundancy in the memory sub-system. Upon detecting an uncorrectable
memory error from a DIMM in a memory cartridge, the processor avoids a system crash by reading the
mirrored DIMM. In this case, the system management routine disables the failed DIMM. Further memory
reads and writes will only occur on the mirrored DIMM.
Limitations to Mirrored Memory mode are as follows:
• 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 and Online Spare mode cannot be enabled simultaneously.
Advanced Memory Protection options are configured in BIOS/Platform Configuration (RBSU) in UEFI
System Utilities. From the System Utilities screen, select System Configuration > BIOS/Platform
Configuration (RBSU)/System Options/Advanced Memory Protection. If the requested AMP mode is
not supported by the installed DIMM configuration, the server boots in Advanced ECC mode.
For more information on the UEFI System Utilities, see the UEFI System Utilities User Guide on the
Hewlett Packard Enterprise website (http://www.hpe.com/info/uefi/docs).
DIMM identification
To determine DIMM characteristics, use the label attached to the DIMM and the following illustration and
table.
Item Description Definition
1
8 GB
16 GB
32 GB
2
1R = Single-rank
2R = Dual-rank
4R = Quad-rank
8R = Octal-rank
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