Acer Altos R920 Series, User Manual

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Memory sparing mode
Sparing is only supported in a lock-stepped (dual-channel)
configuration. Memory sparing is the use of a lock-stepped FBDIMM
rank on a memory branch to provide a backup in case any other lock-
stepped FBDIMM rank on the same branch exceeds a user-selectable
Memory ECC Correctable Error threshold in a fixed time period. This
failure prediction mechanism allows the system to automatically:
• Copy the contents of a failing FBDIMM rank to a backup or spare
FBDIMM rank
• Disable the failing FBDIMM rank
These actions are completed before the FBDIMM rank begins to
generate more serious memory ECC uncorrectable errors that would
bring down the system by corrupting memory.
Spare memory configurations
Spared memory configurations do not provide redundant copies of
memory. In addition, the system cannot continue to operate when an
ECC Uncorrectable Error / Multi-Bit Error (UE/MBE) occurs. The purpose
of memory sparing is to provide runtime failure prediction for FBDIMM
ranks exceeding a specified frequency of ECC Correctable Error events
in a given time period.
The underlying assumption is that FBDIMMs generating increasing
numbers of ECC Correctable Errors are eventually prone to ECC
Uncorrectable Errors. These FBDIMMs should be removed from service
prior to causing a system crash.
Once a FBDIMM rank exceeds the specified frequency of ECC
Correctable Errors the contents of the failing FBDIMM rank are copied
to the spare (reserved) FBDIMM rank. Hardware then isolates and
removes the failing FBDIMM rank from the set of active FBDIMM ranks.
These actions prevent future memory errors and maintain system
integrity.
Note: The memory sparing feature requires that the spare
FBDIMM rank be at least the size of the largest primary FBDIMM
rank in use. When sparing is enabled, the BIOS selects the spare
rank automatically during POST. No manual configuration of this
feature is required beyond turning on the feature in BIOS Setup.
With sparing enabled, the total effective memory size is reduced
by the size of the spare FBDIMM rank(s).